SRF6, a Heat-Responsive Receptor-Like Kinase, Mediates Thermotolerance in Arabidopsis

SRF6, a Heat-Responsive Receptor-Like Kinase, Mediates Thermotolerance in Arabidopsis | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 2 February 2026 V1 Latest version Share on SRF6, a Heat-Responsive Receptor-Like Kinase, Mediates Thermotolerance in Arabidopsis Authors : Hsin-Ying Chang , Chih-Chi Lai , Ya-Chen Huang , Hui-Chen Wu 0000-0002-4991-7616 , and Tsung-Luo Jinn 0000-0002-5185-7691 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.177001777.71754437/v1 172 views 59 downloads Contents Abstract Supplementary Material Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Receptor-like kinases (RLKs) play a central role in plant growth, development, and stress perception. However, their role in heat stress (HS) responses remains poorly understood. Here, we identify STRUBBELIG-RECEPTOR-FAMILY 6 (SRF6) as a heat-inducible, plasma membrane-localized, non-RD RLK that positively regulates thermotolerance in Arabidopsis thaliana . HS significantly induces SRF6 expression, but this induction is markedly reduced in hsfA1a/b/d/e quadruple and hsfA7b mutants, indicating transcriptional control by master HSFs. Although SRF6 lacks detectable kinase activity, its expression persists after heat priming, indicating that it is a heat memory gene. The srf6-1 mutant displays impaired thermotolerance, whereas SRF6 overexpression in srf6-1 restores heat tolerance. Transcriptome analyses reveal that SRF6 functions upstream of multiple stress pathways, ensuring robust induction of HSP22/70/90/101 and CaM3 , while maintaining ER proteostasis via bZIP28/60 and Bip2 . Additionally, SRF6 coordinates the ABA-responsive AREB1/2 and RD29A/B , and ROS-regulatory genes APX1/2 , CAT1 , and RBOHD during HS. In srf6-1 , reduced HSP and ABA/ROS-responsive gene activation, along with increased ER stress, disrupt thermomemory and weaken thermotolerance. Collectively, these findings position SRF6 as a heat-inducible component of HS, linking membrane-associated heat perception to transcriptional reprogramming and thermotolerance. SRF6, a Heat-Responsive Receptor-Like Kinase, Mediates Thermotolerance in Arabidopsis Hsin-Ying Chang 1 , Chih-Chi Lai 1 , Ya-Chen Huang 1 , Hui-Chen Wu 2* , Tsung-Luo Jinn 1* 1 Institute of Plant Biology, National Taiwan University, Taipei, Taiwan 2 Department of Biological Sciences and Technology, National University of Tainan, Tainan, Taiwan * Correspondence: Hui-Chen Wu; [email protected] Tsung-Luo Jinn; [email protected] Email and ORCID of all authors Hsin-Ying Chang [email protected] 0009-0002-7141-5265 Chih-Chi Lai [email protected] 0009-0006-0372-2203 Ya-Chen Huang [email protected] 0000-0002-2090-0378 Hui-Chen Wu [email protected] 0000-0002-4991-7616 Tsung-Luo Jinn [email protected] 0000-0002-5185-7691 ABSTRACT Receptor-like kinases (RLKs) play a central role in plant growth, development, and stress perception. However, their role in heat stress (HS) responses remains poorly understood. Here, we identify STRUBBELIG-RECEPTOR-FAMILY 6 (SRF6) as a heat-inducible, plasma membrane-localized, non-RD RLK that positively regulates thermotolerance in Arabidopsis thaliana . HS significantly induces SRF6 expression, but this induction is markedly reduced in hsfA1a/b/d/e quadruple and hsfA7b mutants, indicating transcriptional control by master HSFs. Although SRF6 lacks detectable kinase activity, its expression persists after heat priming, indicating that it is a heat memory gene. The srf6-1 mutant displays impaired thermotolerance, whereas SRF6 overexpression in srf6-1 restores heat tolerance. Transcriptome analyses reveal that SRF6 functions upstream of multiple stress pathways, ensuring robust induction of HSP22/70/90/101 and CaM3 , while maintaining ER proteostasis via bZIP28/60 and Bip2 . Additionally, SRF6 coordinates the ABA-responsive AREB1/2 and RD29A/B , and ROS-regulatory genes APX1/2 , CAT1 , and RBOHD during HS. In srf6-1 , reduced HSP and ABA/ROS-responsive gene activation, along with increased ER stress, disrupt thermomemory and weaken thermotolerance. Collectively, these findings position SRF6 as a heat-inducible component of HS, linking membrane-associated heat perception to transcriptional reprogramming and thermotolerance. Key words: Receptor-like kinase, Heat shock response, Heat stress memory, Non-RD type RLK, Thermotolerance. 1 Introduction Global warming has caused substantial alterations in Earth’s climate, exacerbating environmental stresses that compromise plant growth and development, and contributing to global declines in crop yields (Hansen et al., 2012; Hultgren et al., 2025). Environmental stress refers to any external factor that limits optimal plant growth and biomass accumulation over time (Lichtenthaler, 1998). Enhancing plant stress tolerance and mitigating these adverse effects necessitate a detailed understanding of the molecular and cellular mechanisms underlying stress perception and adaptation (Lamers et al., 2020; Ding and Yang, 2022). Among abiotic stressors, elevated temperature is among the most detrimental, particularly during sensitive developmental stages (Resentini et al., 2023). When temperatures exceed plant tolerance thresholds, heat stress (HS) occurs, accelerating development at the expense of biomass and reproductive success, thereby reducing yield (Fahad et al., 2017; Firmansyah and Argosubekti, 2020). HS disrupts cellular homeostasis by causing protein misfolding, enzyme inactivation, membrane destabilization, and excessive accumulation of reactive oxygen species (ROS), collectively impairing transcription, translation, and genome stability (Purschke et al., 2010; Guihur et al., 2022; Thomas et al., 2022). These stress-induced changes are sensed by “heat stress sensors”, distinct from thermosensors that directly monitor temperature, thereby enabling plants to detect non-articulate stress signals (Calixto, 2025). To mitigate such damage, plants activate DNA repair, protein quality control, and protective signaling pathways to maintain genome integrity (Han et al., 2021). Moreover, heat priming enhances thermotolerance by restoring translation, stabilizing heat-responsive transcripts, promoting the unfolded protein response, and modulating co-translational mRNA decay (Dannfald et al., 2025). Collectively, these processes constitute the integrated HS response (HSR). The HSR in plants is orchestrated by heat shock factors (HSFs), which bind to conserved heat shock elements (HSEs) in the promoters of thermoresponsive genes to activate protective gene expression programs that alleviate heat-induced damage and maintain cellular homeostasis (Scharf et al., 2012; Dündar et al., 2025). HSFs in Arabidopsis thaliana (Arabidopsis) are categorized into three major groups: HSFA (A1–A9), HSFB (B1–B4), and HSFC (C1) (Scharf et al., 2012). Among them, HSFA1 isoforms (HSFA1a, HSFA1b, HSFA1d, and HSFA1e) act as master regulators, initiating the expression of heat shock proteins (HSPs) and downstream transcription factors (Liu and Charng, 2013), while HSFA2, under the control of HSFA1d/e, reinforces prolonged thermotolerance (Charng et al., 2007; Nishizawa-Yokoi et al., 2011). Other HSFs contribute to stress-specific responses, including pathogen and ROS signaling (HSFA4/5), ABA-mediated thermotolerance (HSFA6b), drought adaptation (HSFA7b), and fine-tuning of HSR (HSFB1/2b) (Baniwal et al., 2007; Huang et al., 2016; Zang et al., 2019). HSFC1 remains poorly characterized, with no direct evidence for its role in HS. Beyond transcriptional and metabolic reprogramming, HSR involves stress perception and signal transduction, with HS sensors playing a key role in detecting cellular changes (Calixto, 2025). Arabidopsis encodes over 600 receptor-like kinases (RLKs), which are crucial components of stress signaling networks (Gandhi and Oelmüller, 2023). Structurally, RLKs consist of a signal peptide, an extracellular domain that senses extracellular cues, and a cytoplasmic kinase domain (KD) that transduces signals through phosphorylation cascades (Jose et al., 2020). Only a subset of RLKs has been functionally linked to HSR. For example, the bri1-301 mutant, which carries a nonfunctional KD, exhibits a dwarf phenotype under HS (Zhang et al., 2018). In pepper ( Capsicum annuum ), CaHSL1 positively regulates thermotolerance downstream of the transcription factor CaWRKY40, which binds to the W-box of the CaHSL1 promoter (Guan et al., 2018). By contrast, CaWAKL20 negatively affects thermotolerance by suppressing ABA-responsive genes (Wang et al., 2019). A large-scale phenotyping study further identified 14 RLK T-DNA mutants with altered thermotolerance, though their precise molecular roles in HS signaling remain unknown (Li et al., 2018). In this study, the receptor-like kinase gene STRUBBELIG-RECEPTOR FAMILY 6 (SRF6; At1g53730) was identified in the AtGenExpress data sets as highly responsive to HS at 37°C, a pattern further validated by qRT-PCR. Promoter analysis identified putative HSEs, implicating HSF-mediated regulation. Expression profiling in HSF mutant backgrounds indicated that HSFA1s and HSFA7b contribute to SRF6 regulation. Subcellular localization confirmed SRF6 as a membrane-bound protein, and in vitro kinase assays indicated that its kinase domain is atypical and lacks autophosphorylation activity. The srf6 mutant exhibited reduced induction of HSP genes, accompanied by enhanced expression of ER stress-responsive genes. Together, these findings reveal a previously uncharacterized role of SRF6 in HS resilience and underscore the broader contribution of RLKs to thermotolerance mechanisms in plants. 2 Materials and Methods 2.1 Plant Materials and Growth Conditions Arabidopsis thaliana (ecotype Col-0) was used in this study. T-DNA insertion mutants included srf6-1 (SALK_054337C; At1g53730 ), srf6-2 (SALK_139842C; At1g53730 ), hsfa2 (SALK_008978; At2g26150 ), hsfa6b (GK-513A02; At3g22830 ; Huang et al., 2016), hsfa7a (SAIL_450_G04; At3g51910), and hsfa7b (SALK_152004; At3g63350), obtained from the Arabidopsis Biological Resource Center (ABRC) or the Nottingham Arabidopsis Stock Centre (NASC). The hsfA1a/b/d/e quadruple mutant was provided by Dr. Yee-yung Charng (Liu et al., 2011). Seedlings were grown on solid half-strength Murashige and Skoog (1/2 MS; Sigma M5519) basal medium (Murashige and Skoog, 1962) supplemented with 1% sucrose and 0.8% phytagel, under controlled conditions (22–24°C, 8 h dark/16 h light, 80–100 µmol m⁻² s⁻¹ light intensity). Transgenic plants were generated in the Col-0 and srf6-1 backgrounds via Agrobacterium tumefaciens strain GV3101-mediated floral dip transformation (Clough and Bent, 1998). Transformants were selected on 0.5× MS medium containing 10 µg/ml hygromycin or by foliar application of 0.4% BASTA herbicide. 2.2 Genome-wide Transcriptional Expression Analysis of Arabidopsis Receptor-like kinase (RLK) and Receptor-like Protein (RLP) Genes To examine the gene expression profiles of Arabidopsis RLKs and RLPs under heat shock (HS), candidate RLK and RLP genes were compiled based on prior research (Shiu et al., 2004; Wang et al., 2008). The normalized signals for these candidate genes were analyzed and displayed using the microarray database (ME00339) from the AtGenExpress consortium (http://www.arabidopsis.org/info/expression/). 2.3 RNA Preparation, cDNA Synthesis, and Quantitative Real-time PCR (qRT-PCR) Total RNA was extracted using TRIZOL reagent (Invitrogen) and the TURBO DNA-free Kit (Applied Biosystems) to remove genomic DNA contamination. Complementary DNA (cDNA) was synthesized from the purified RNA with the High-Capacity cDNA Reverse Transcription Kit (Applied Biosystems). qRT-PCR was performed using iQ SYBR Green Supermix (Bio-Rad), with fluorescence signals monitored on a MyiQ thermocycler (Bio-Rad) and processed with the iQ5 software package (Bio-Rad). Each target was analyzed in triplicate, and relative expression levels were determined using the 2 −ΔΔCt method described by Livak and Schmittgen (2001). Gene expression values were normalized to the reference gene PP2AA3 ( PP2A ; At1g13320) (Czechowski et al., 2005). 2.4 Construction and Generation of Transgenic SRF6 Reporter, Overexpression, and Complementation Lines The 1.471-kb SRF6 promoter region was amplified and subcloned into the BamHI sites of pCAMBIA1391Z (CAMBIA) to generate SRF6-promoter::GUS reporter lines. The coding sequence (CDS) of SRF6, excluding the stop codon (2160 bp), was amplified by RT-PCR and cloned into the Gateway vector pCR8/GW/TOPO (Invitrogen) for sequencing. The CDS of SRF6 was then recombined into the modified destination vectors pCAMBIA3300 (CAMBIA) and pEarleyGate 101 (ABRC) via Gateway LR reaction to generate 35S::SRF6 with a 3xFLAG tag and an enhanced yellow fluorescent protein (YFP) tag at its C terminus, respectively. The 35S::SRF6-3xFLAG transgene was transformed into the Col and srf6-1 mutant backgrounds to generate the overexpression and complement lines, respectively. The 35S::SRF6-YFP transgene was used for subcellular localization analysis. 2.5 Protoplast Preparation and Transient Expression Assay Protoplast preparation and transfection were performed as previously described (Yoo et al., 2007). For protoplast preparation, 3–4-week-old Arabidopsis rosette leaves were collected before flowering. Each transfection reaction contained 10–20 μg of plasmid DNA and at least 2×10 4 protoplasts. After transfection, the reaction was incubated at 22°C under continuous light for 16–24 hours, and the results were examined by confocal microscopy (TCS SP5, Leica). 2.6 Subcellular Localization Analysis The CDS of SRF6 was inserted into the expression vector pEarleyGate 101 (ABRC) to create fusion proteins with enhanced YFP at the C-terminus ( 35S::SRF6-YFP ). Simultaneously, a plasma membrane marker labeled with mCherry red fluorescent protein (RFP) (Nelson et al., 2007) was co-expressed with SRF6-YFP. The YFP signal was detected with 488 nm excitation and 505 to 530 nm emission, while the mCherry signal was observed with 543 nm excitation and 560 to 615 nm emission. Additionally, chlorophyll autofluorescence was detected between 630 and 680 nm. 2.7 Thermotolerance Test Seven-day-old seedlings were grown on 1/2 MS medium plates for the thermotolerance test. Plates were sealed with plastic electrical tape and then incubated in a water bath to assess basal thermotolerance (BT), short-term acquired thermotolerance (SAT), long-term acquired thermotolerance (LAT), and gradient heat stress (GHS), as previously described (Charng et al., 2007; Yeh et al., 2012; Huang et al., 2016). The number of healthy growing seedlings was counted 10 days after the heat treatment. 2.8 In Vitro Kinase Assay The SRF6-KD amplicon was ligated into the pMAL-c5X vector using Nco I and Bam HI restriction sites, and E. coli BL21 cells were used for recombinant protein expression. According to Taylor et al. (2013), cells from a single colony were grown in 1 mL LB medium at 37°C with shaking for over 20 h, then transferred to 50 mL LB medium and cultured for 3 h until the OD 600 reached 0.6–0.8. Protein expression was induced with 1 mM IPTG at 28°C for 4 h. Cell pellets were boiled in 1× SDS sample buffer (62.5 mM Tris-HCl, pH 6.8, 2% SDS, 10% glycerol, 50 mM DTT, 0.005% bromophenol blue) for 3 min, then centrifuged at 12,000 rpm. 20 μL of the supernatant was analyzed by 8% SDS-PAGE. Total protein was stained with Coomassie Brilliant Blue overnight at room temperature, then destained with 40% methanol and 10% acetic acid. For phosphoprotein staining, the gel was fixed in 50% methanol and 10% acetic acid for 30 min, then incubated overnight with a fresh solution. After fixation, the gel was washed with deionized water and stained with 1/3× Pro-Q Diamond (Thermo Fisher Scientific) for 2 h in the dark. A destaining solution of 20% acetonitrile and 50 mM sodium acetate (pH 4.0) was used before signal detection, and analysis was performed using the UVP ChemStudio Imaging Systems (Analytik Jena AG). 2.9 Site-directed Mutagenesis The megaprimer PCR method (Tyagi et al., 2004) was modified to generate the SRF6-KD-K444E mutant. Two complementary oligonucleotides carrying the desired mutation were designed (Supplementary Table 1), and the mutant sequence was amplified by PCR. In this modified approach, an additional megaprimer complementary to the original was introduced to generate two template strands in the first PCR. These templates were then combined and used in a second PCR to produce the final mutant construct. 2.10 Statistical Analysis Three technical and biological repeats were performed. Independent Student’s t -test (two-tailed) and Tukey-Kramer tests were used to compare differences across all tests. A p -value less than 0.05 was considered statistically significant. 2.11 Primers Primers used in this research are given in Supplementary Table 1 . 3 Results 3.1 Validation of the SRF6 Transcript Level Under Heat Shock To characterize the gene expression profiles of RLK and RLP genes in response to heat stress (HS), we analyzed transcriptome data from the AtGenExpress consortium. Among 610 RLK and 57 receptor-like protein (RLP) genes reported in Arabidopsis (Shiu and Bleecker, 2001, 2003), we identified those upregulated by HS at 37°C in root and shoot tissues (Figure 1a). Notably, SRF6 (At1G53730) expression was apparently induced by HS in both roots and shoots. To validate this, we performed qRT-PCR to examine SRF6 expression under the 37°C HS treatment. Seven-day-old wild-type Columbia (Col) seedlings were exposed to HS at 37°C for 0.5–3 h, followed by recovery at 22°C for 1–3 h (Figure 1b, top). qRT-PCR analysis showed that SRF6 transcript levels increased significantly during HS but declined during recovery, consistent with the microarray data (Figure 1b, middle). HSP18.2 , a heat-responsive gene, served as a positive control (Figure 1b, bottom), and PP2A was used as the internal reference gene. 3.2 SRF6 Expression Is Regulated by HSFA1s and HSFA7b and Exhibits Distinct Tissue-Specific Patterns To investigate the regulation of SRF6 expression under HS, we first analyzed its 2-kb promoter region using the Plant Promoter Analysis Navigator (PlantPAN4.0; https://plantpan.itps.ncku.edu.tw/plantpan4/index.html) (Chow et al., 2024) (Figure S1). Three predicted HSEs were identified, suggesting that HSFs may regulate SRF6 expression. To validate this, we examined SRF6 expression in mutant lines lacking key heat shock transcription factor (HSF) genes, including the hsfA1a/b/d/e quadruple mutant ( hsfa1qk ) and the single mutants hsfA2 , hsfA6b , hsfA7a , and hsfA7b (Figure 2). qRT-PCR analysis showed that SRF6 induction was significantly reduced in hsfa1qk and hsfA7b mutants, whereas no marked changes were observed in hsfa2 , hsfa6b , or hsfa7a mutants (Figure 2). These results demonstrate that HSFA1s and their downstream factor HSFA7b (Liu et al., 2011) act as critical regulators of SRF6 expression in response to HS. To further characterize the spatial distribution of SRF6 , we generated SRF6 -promoter:: GUS transgenic lines carrying a 1,471 bp promoter fragment. Histochemical staining of SRF6- promoter:: GUS transgenic plants revealed strong expression in the hypocotyl, shoot apical meristem, and vascular bundles (Figure S2a, b). GUS activity was also observed in roots and emerging lateral roots of 3-, 7-, and 16-day-old seedlings, whereas only weak signals were detected in the root cap and root apical meristem (Figure S2c). In reproductive tissues, SRF6 was expressed in inflorescence stems, sepals, pistils, and abscission zones. This expression was developmentally regulated, as transcripts were undetectable in mature seeds (Figure S2d – f). Together, these results indicate that SRF6 is transcriptionally regulated by HSFA1s and HSFA7b in response to HS and exhibits distinct tissue-specific expression patterns throughout development. 3.3 SRF6 Localizes to the Plasma Membrane and Functions as an Atypical RLK Sequence analysis revealed that SRF6 contains an N-terminal signal peptide and a transmembrane domain, indicative of plasma membrane localization (Eyüboglu et al., 2007). To validate this, we generated a full-length SRF6 fusion with yellow fluorescent protein at the C-terminus (SRF6-YFP) and expressed it in Arabidopsis protoplasts. Confocal imaging showed that SRF6-YFP co-localized with the plasma membrane marker PM-RFP (mCherry-tagged), confirming SRF6 localization at the plasma membrane (Figure 3). In addition to its membrane association, SRF6 encodes a non-arginine-aspartate (non-RD) kinase that contains a LysAsn (KN) motif at residues 543 and 544, replacing the canonical RD motif (Figure S3a). To assess its kinase activity, we purified the recombinant cytoplasmic kinase domain (SRF6-KD, amino acids 325–720) fused to maltose-binding protein (MBP-SRF6-KD) for the in vitro assay (Figure S3b). Both MBP-SRF6-KD and its kinase-dead mutant Lys444Glu (K444E) were successfully induced by IPTG (Figure 4a, top). Additionally, as a positive control, we used the auto-phosphorylating RLK HAESA (HAE)-KD and its kinase-dead mutant K711E (Taylor et al., 2013) (Figure 4a, bottom). Phosphorylation status was assessed by Pro-Q Diamond staining (Figure 4b, top), and protein loading was confirmed by Coomassie Brilliant Blue staining (Figure 4b, bottom). Unlike MBP-HAE-KD, which showed strong autophosphorylation (Figure 4b, lane 2), MBP-SRF6-KD showed no detectable signal (Figure 4b, lane 6). The kinase-dead HAE-KD mutant (Figure 4b, lane 4) served as a negative control, further validating the assay. Together, these findings indicate that SRF6 lacks detectable kinase activity and likely functions as an atypical RLK. 3.4 SRF6 Is a Potential Heat Memory Gene Plants can acquire HS memory, enabling sustained thermotolerance and stronger responses upon re-exposure (Charng et al., 2007; Lämke et al., 2016). To assess whether SRF6 functions as a heat memory gene, we performed qRT-PCR analysis following the experimental framework described by Liu et al. (2018). SRF6 transcript levels were analyzed under control (CK), heat primed (P), heat triggered (T), and combined primed + triggered (P+T) conditions (Figure 5a). A gene with higher expression in P+T than in T indicates heat stress memory. The known memory gene AZF3, defined by a (P+T)/T ratio greater than 2, served as a positive control (Liu et al., 2018). Consistent with this criterion, SRF6 expression during the P+T phase was significantly higher than during the T phase, yielding a (P+T)/T ratio of 2.1 (Figure 5b). These results suggest that SRF6 may function as an HS memory gene. 3.5 SRF6 T-DNA Insertion Mutants Reveal Their Role as a Positive Regulator of Thermotolerance To investigate the role of SRF6 in the HSR, we analyzed two T-DNA insertion lines, srf6-1 and srf6-2 , by PCR-based genotyping (Figure S4a and b). srf6-1 contains a T-DNA insertion in the 12 th exon, while srf6-2 has an insertion in the 5’ UTR. Both were confirmed as homologous T-DNA insertion lines by genotyping. qRT-PCR analysis showed a significant decrease in SRF6 transcript abundance in both srf6-1 and srf6-2 compared to Col under HS conditions (Figure S4c), thereby validating these lines as reliable genetic materials for functional characterization. Because SRF6 expression is completely lost in srf6-1 , we chose this line for subsequent experiments. To investigate the role of SRF6 in thermotolerance, we compared the performance of srf6-1 with that of wild-type Col and the heat-sensitive hsp101 mutant (Queitsch et al., 2000) using established assays (Yeh et al., 2012). In the basal thermotolerance (BT) test, srf6-1 seedlings showed a significantly lower survival rate than Col (Figure 6a). Similar reductions were observed under short-term acquired thermotolerance (SAT; Figure 6b), long-term acquired thermotolerance (LAT; Figure 6c), and gradient heat stress (GHS; Figure 6d) assay conditions. 3.6 Overexpression of SRF6 Restores Thermotolerance in srf6 -1 Mutant To further validate the role of SRF6 in thermotolerance, we generated transgenic plants overexpressing the SRF6-3xFLAG transgene in both the Col and srf6-1 backgrounds. We confirmed expression of the SRF6-3xFLAG transgene in 7-day-old seedlings by immunoblotting with an anti-Flag antibody (Figure 7a) and qRT-PCR (Figure 7b). Notably, overexpression of SRF6 in the srf6-1 background (lines H3 and J5) restored the mutant phenotype to that of Col plants. Meanwhile, the overexpression lines Q3 and R4 in the Col background still displayed a phenotype similar to that of Col in the SAT test (Figure 7c). These findings suggest that SRF6 is required to maintain thermotolerance and functions as a positive regulator in the HSR. 3.7 Expression of Abiotic Stress-responsive Genes in Srf6-1 Mutant Under HS Consistent with its reduced heat tolerance, the srf6-1 mutant showed altered expression of multiple stress-responsive genes (Figure 8) . Under control conditions, srf6-1 exhibited higher transcript levels of HSP70 , HSP90 , HSP101 , and CaM3 than Col. Upon HS at 37°C, HSP70 expression declined at 1 h (HS1h) and 3 h (HS3h). HSP90 and HSP101 were significantly reduced after HS1h and HS3h, respectively. In contrast, CaM3 was significantly upregulated at HS3h and remained elevated during the subsequent 1 h of recovery (R1h). HSP22 expression was lower under both control and stress conditions but returned to Col levels during recovery, whereas HSP18.2 remained unchanged across all treatments (Figure 8a). ER stress-related genes Bip2 , bZIP28 , and both unspliced and spliced forms of bZIP60 were consistently upregulated in srf6-1 across all treatments (Figure 8b). The ABA-responsive gene AREB1 was markedly reduced after HS3h and R1h, whereas AREB2 and RD29A expression decreased under control, HS1h, and recovery conditions. RD29B expression was higher under HS1h and R1h in srf6-1 than in Col (Figure 8c). In srf6-1 , ROS-responsive genes were differentially regulated, with APX1 reduced under control conditions, APX2 elevated under control conditions, and HS3h, CAT1 decreased after 1 h and 3 h of HS, and RBOHD downregulated under control and HS3h (Figure 8d). \sout 4 Discussion 4.1 SRF6 as a Novel Heat-Inducible Receptor-Like Kinase Beyond transcriptional and metabolic reprogramming, HSR relies on precise perception and signal transduction, with HS sensors serving as the first line of defense against heat-induced cellular perturbations (Calixto, 2025). Among these, RLKs are notable for integrating diverse extracellular cues, including hormones, pathogen signals, and stress peptides, into intracellular responses via reversible phosphorylation. Although the Arabidopsis genome encodes more than 600 RLKs, most remain functionally uncharacterized under HS. Analysis of the AtGenExpress database revealed strong induction of SRF6 transcripts under HS (Figure 1a), a pattern confirmed by qRT-PCR, which showed a fivefold increase after 3 h of heat exposure (Figure 1b). This induction suggests that SRF6 may function as a signaling component in the HSR, potentially linking extracellular heat perception to downstream transcriptional reprogramming. Promoter analysis further identified three HSEs in the SRF6 promoter (Figure S1), suggesting regulation by canonical HSFs. In agreement, SRF6 expression was markedly reduced in the hsfA1a/b/d/e quadruple mutant and in the hsfA7b mutant, but remained unaffected in the hsfA2 , hsfA6b , and hsfA7a mutants ( Figure 2 ). These patterns align with the established roles of HSFA1s as master regulators of the early HSR and HSFA7b as a modulator of thermomemory in the shoot apical meristem (Liu et al., 2011; Ohama et al., 2017; John et al., 2024). Consistent with this connection, SRF6 expression during the post-stress plus trigger phase (P+T) was more than twice that observed during the trigger phase (T) alone, yielding a (P+T)/T ratio of 2.1, suggesting sustained transcriptional activation characteristic of HS memory genes (Figure 5). Functional evidence further supports a positive regulatory role, as the srf6-1 knockout showed reduced thermotolerance (Figure 6). Complementation lines J5 and H3 ( SRF6- OE /srf6-1 ) restored the mutant phenotype to wild-type Col levels, whereas lines Q3 and R4 ( SRF6 -OE/Col) retained a Col-like phenotype in the SAT assay (Figure 7c). The structural and evolutionary context of SRF6 underscores its functional relevance. SRF6 belongs to the LRR-V/SRF gene family, a small group of nine members with diverse, context-dependent functions. Notably, this family includes SRF3, which mediates iron-dependent immune sensing (Platre et al., 2021), SRF4, a regulator of leaf size (Eyüboglu et al., 2007), and SRF9 (SUB), which governs ovule development and positional signaling (Schneitz et al., 1995; Chevalier et al., 2005; Chaudhary et al., 2020). The heat inducibility of SRF6 thus reveals a previously unrecognized branch of this family engaged in abiotic stress signaling. Similar RLKs have been implicated in thermotolerance across species. For example, the tomato LRR-RLK MRK1 is essential for heat tolerance and regulates HSFA1a (Ma et al., 2022), while the wheat LRR-RLK TaSERK1 enhances heat tolerance by interacting with HSPs (Shi et al., 2023). Taken together, these findings suggest that SRF6 acts downstream of HSFA1s and is fine-tuned by HSFA7b, making it an integral component of the transcriptional cascade that coordinates both the acute and sustained phases of the HSR. More broadly, the involvement of SRF6 highlights a potential signaling module in which RLKs function as effectors of HSF-mediated transcriptional programs, thereby linking stress perception at the cell surface with long-term transcriptional memory and plant thermotolerance. 4.2 Atypical Kinase Properties of SRF6 and Implications for HS Signaling Molecular characterization of SRF proteins revealed that SRF6 harbors an atypical kinase domain (KD) (Eyüboglu et al., 2007), classified as a non-arginine-aspartate (non-RD) type kinase due to the absence of the conserved arginine (R543) adjacent to the catalytic aspartate (D544) in the activation loop (Figure S3) . Such non-RD-type kinases are often associated with alternative activation modes in environmental signaling (Dardick et al., 2012), suggesting that SRF6 may function through unique regulatory mechanisms. Biochemical analyses confirmed the absence of intrinsic autophosphorylation in SRF6-KD despite robust protein accumulation (Figure 4) , consistent with expectations for non-RD type kinases. In contrast, canonical RD kinases such as HAESA (HAE) readily undergo autophosphorylation under similar conditions (Taylor et al., 2013). This lack of detectable catalytic activity supports the classification of SRF6 as an atypical kinase whose activation likely depends on extrinsic factors rather than intrinsic auto-phosphorylation. Such dependency is well established in other non-RD type RLKs. For instance, FLAGELLIN-SENSING 2 (FLS2) and EF-TU RECEPTOR (EFR) rely on association with the RD co-receptor BAK1/SERK family to initiate signal transduction (Chinchilla et al., 2007). More broadly, non-RD type RLKs are increasingly recognized as regulated sensors that act within receptor complexes rather than as autonomous enzymes, with activation often requiring extracellular ligand perception, heteromerization with catalytically active partners, or scaffolding interactions (Antolín-Llovera et al., 2012; Hohmann et al., 2017). These parallels suggest that SRF6 may function similarly as a co-receptor-dependent signaling hub that integrates extracellular heat cues. Moreover, receptor cooperation is a well-established mechanism for fine-tuning signal perception in plants. For instance, BRASSINOSTEROID-INSENSITIVE 1 (BRI1) and its co-receptor BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) coordinate brassinosteroid (BR) signaling that regulates seed germination, fertility, stem elongation, flowering, and senescence (Clouse et al., 1996; He et al., 2000; Li et al., 2002). Similarly, the HAESA (HAE) and HAESA-LIKE 2 (HSL2) heterodimer controls floral abscission through a MAPK cascade (Jinn et al., 2000; Cho et al., 2008). In addition, several atypical RLKs transmit signals through phosphorylation-independent mechanisms; for example, the maize atypical receptor kinase (MARK) activates a GCK-like kinase (MIK) via conformational changes rather than direct phosphorylation (Castells et al., 2006), and ARABIDOPSIS CRINKLY 4 (ACR4) can function without its own catalytic activity, as an ACR4 kinase-dead mutant rescues the acr4 mutant phenotype through interaction with AtCRR2 (Cao et al., 2005; Gifford et al., 2005). These examples demonstrate that RLK signaling employs diverse activation modes, including co-receptor assistance and phosphorylation-independent pathways, suggesting that SRF6, as an atypical non-RD kinase, may likewise depend on partner proteins or alternative mechanisms to mediate HSR. Consistent with this notion, evidence from SRF family homologs supports functional divergence in kinase dependence. Arabidopsis SRF9 requires its KD for function despite lacking detectable kinase activity, as kinase-dead variants can rescue ovule defects (Vaddepalli et al., 2011). In contrast, StLRPK1, a potato homolog of Arabidopsis SRF3, requires its kinase activity to initiate MAPK signaling for immunity (Wang et al., 2018), whereas ScORK28, related to SRF6 and SRF7 in Solanum chacoense , functions as an active Mg²⁺-dependent protein kinase (Germain et al., 2007). Together, these findings suggest that SRF6 may be activated through interaction with a partner kinase or may function as a kinase-dead receptor, mediating phosphorylation-independent signaling and thereby serving as a versatile integrator within the HS signaling network. 4.3 SRF6 Modulates a Subset of Heat Shock and ER Stress Responses HS perception in plants involves both physical and biochemical mechanisms. A bona fide HS sensor is defined by three criteria: its properties are directly altered by HS, these changes trigger a signaling cascade, and the resulting pathway drives adaptive responses (Vu et al., 2019). HS can act as a physical cue detected externally by thermosensors, or as intracellular signals such as Ca²⁺ fluctuations and ROS production, which are perceived by HS sensors (Lamers et al., 2020; Calixto, 2025). This framework refines our understanding of HS signaling and provides a conceptual basis for identifying both primary HS perception mechanisms and heat-associated signaling pathways mediated by RLKs. In srf6-1 , elevated basal expression of HSP70 , HSP90 , and HSP101 , as well as CaM3 , a Ca 2+ -responsive gene under normal growth conditions (Figure 8a) , suggests constitutive activation or impaired repression of the HSR. Normally, HSP70 and HSP90 act as molecular chaperones that bind HSFs and maintain them in an inactive monomeric state. Upon HS, misfolded proteins sequester HSP70 and HSP90, thereby releasing HSFs for trimerization and transcriptional activation of HSPs (Wu et al., 2018). Consistent with this model, srf6-1 shows elevated basal HSP70 and HSP90 , which may disrupt HSF-chaperone dynamics and reduce proper HSP induction upon HS. These observations indicate that SRF6 selectively modulates a subset of chaperones critical for proteostasis and cellular protection during HS. Conversely, ER stress-related genes under HS, including Bip2 , bZIP28 , and bZIP60s , were upregulated in srf6-1 (Figure 8b) , consistent with compensatory activation of ER quality control (ERQC) pathways. Because ERQC stabilizes temperature-sensitive RLKs such as bri1-301 and SRF9 (Lv et al., 2018; Vaddepalli et al., 2011), SRF6 may also depend on ERQC for proper folding and function. The enhanced ER stress responses observed in srf6-1 mutants provide important mechanistic insights into the function of SRF6. Under HS, misfolded proteins normally accumulate in ER, but strong HSP induction alleviates the stress and maintains proteostasis (Mas-ud et al., 2025). In srf6-1 , HSP induction was significantly reduced, which may lead to insufficient protein quality control and consequently elevated expression of ER stress markers such as Bip2 , bZIP28 , and bZIP60 (Iwata and Koizumi, 2005; Liu et al., 2007; Gao et al., 2008). This indicates that SRF6 acts upstream to ensure efficient HSP induction, thereby minimizing ER stress under HS. The persistence of SRF6 expression after heat priming, together with the attenuated induction of HSP in mutants, suggests a role in thermomemory. By sustaining HSP expression, SRF6 enables plants to mount stronger responses upon repeated HS exposure, a hallmark of memory genes (Lämke et al., 2016). In its absence, plants rely more heavily on ER stress signaling as a compensatory mechanism, which provides only limited protection and reduces thermotolerance. Beyond its role in HSP regulation, SRF6 also modulates hormonal and redox pathways. In srf6-1 , the downregulation of ABA-responsive genes AREB1 , AREB2 , and RD29A , but not RD29B , indicates a selective attenuation of ABA-dependent stress signaling under HS. ABA acts as a key regulator of thermotolerance by promoting stomatal closure and induction of stress-protective genes (Yoshida et al., 2014). Transcription factors AREB1 and AREB2 regulate the expression of RD29A and RD29B during dehydration and HS (Fujita et al., 2013). RD29A can also be induced through AREB- and ABA-independent pathways, whereas RD29B expression is strongly ABA-dependent (Narusaka et al., 2003). The selective reduction of RD29A in srf6-1 suggests that SRF6 primarily influences the branch of ABA signaling or upstream stress perception that converges on AREB-mediated, ABA-independent RD29A activation. This partial attenuation of ABA signaling likely contributes to the reduced thermotolerance of srf6-1 , consistent with the requirement for ABA pathways in heat-induced protection. Meanwhile, altered expression of ROS-responsive genes in srf6-1 suggests that SRF6 also contributes to maintaining cellular redox balance under HS. The reduced basal level of APX1 , a key cytosolic H₂O₂-scavenging enzyme, indicates compromised antioxidant capacity even before stress exposure. In contrast, APX2, rapidly induced by heat and oxidative signals, was elevated under both control and HS conditions, possibly reflecting a compensatory response to excessive ROS accumulation (Panchuk et al., 2002). The downregulation of CAT1 and RBOHD further supports the notion of disturbed ROS homeostasis, as CAT1 detoxifies H₂O₂ in peroxisomes and RBOHD mediates controlled ROS bursts essential for stress signaling (Torres et al., 2002). Together, these transcriptional changes indicate that SRF6 fine-tunes the interplay between ABA and ROS signaling during HS adaptation. The dual attenuation of ABA-dependent gene activation and redox regulation in srf6-1 likely disrupts stress signal integration, thereby compromising cellular protection and recovery under prolonged HS. 5 Conclusion Collectively, our findings identify SRF6 as a key regulatory hub linking RLK-mediated heat perception at the plasma membrane to transcriptional programs that govern HSP induction, ER quality control, ABA signaling, and ROS homeostasis. Its plasma membrane localization and non-RD kinase domain classify SRF6 as a sensor-like RLK with limited intrinsic kinase activity. Acting downstream of HSFA1s and regulated by HSFA7b, SRF6 mediates heat memory and sustained thermotolerance by triggering Ca²⁺ and ROS signaling that activate HSPs, ABA-responsive genes, and redox regulators. Loss of SRF6 disrupts these pathways, resulting in impaired HSP induction, ER stress, and dysregulated ABA and ROS signaling (Figure 9). Thus, SRF6 is a previously unrecognized LRR-V/SRF family member that integrates membrane-based heat perception with transcriptional memory and plant thermotolerance. \sout Funding This work was supported by the National Science and Technology Council (NSTC) (Grant nos. NSTC 112-2311-B-002-020, NSTC 113-2311-B-002-016, and NSTC 114-2311-B-002-020) and National Taiwan University (Grant nos. NTU-CC-114L893202 and NTU-CC-115L891902) to TLJ. It was also supported by NSTC and the Ministry of Education, Taiwan (112-2311-B-002-020, PAG107012, and PAG1100168) to HCW. We thank the NTU Confocal Microscope Laboratory for performing fluorescence imaging. Authors’ contributions HYC and CCL were responsible for sample collection, experimental procedures, data analysis, figure and table preparation, and contributed to the initial manuscript draft. 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(a) A total of 610 RLK and 57 RLP genes were profiled, revealing 25 HS-induced candidates. Among them, SRF6 (At1G53730) showed a strong response. The heatmap color scale represents transcript abundance, from low (blue) to high (red). Microarray data were obtained from the AtGenExpress consortium (http://www.arabidopsis.org/info/expression/ATGen Express.jsp). (b) SRF6 expression was validated by qRT-PCR. Expression values were normalized to the control (CK). HSP18.2 , a heat-responsive gene, served as a positive reference. PP2A was used as the internal control for normalization. Data represent mean ± SD (n = 3), with significance determined by Student’s t test (* P < 0.05). Figure 2. Expression of SRF6 in HSF-mutant plants under heat stress. Seven-day-old seedlings of four HSF -mutant lines were maintained under control conditions (CK) or exposed to heat stress (HS) at 37°C for 1–3 h (HS1h–HS3h), followed by recovery at 22°C for 1 h (R1h). The pictograms illustrate the HS treatment scheme and sampling times. SRF6 expression in (a) hsfA1qk , (b) hsfA2 , (c) hsfA6b , and (d) hsfA7a and hsfA7b mutants was analyzed by qRT-PCR. Expression levels were normalized to the Col CK. Data are presented as mean ± SD (n = 3). Asterisks (*) indicate significant differences compared to Col ( P < 0.05; Student’s t -test). PP2A served as the internal reference gene. Figure 3. Subcellular localization of SRF6. The SRF6 protein was fused to the N-terminus of yellow fluorescent protein (SRF6-YFP) and co-expressed with a plasma membrane marker labeled with mCherry (PM-RFP) in protoplasts, as indicated. Chloroplasts are shown in blue due to their autofluorescence. YFP served as a control in this experiment. Scale bar = 20 μm. Figure 4. Evaluation of the autophosphorylation capability of recombinant MBP-SRF6-KDs. (a) IPTG induction of MBP-SRF6-KD and MBP-HAESA (HAE)-KD (positive control) in E. coli , with (+) or without (-) 1 mM IPTG for 2–16 h, as indicated. Total proteins were separated by 8% SDS-PAGE. The molecular weights of the recombinant MBP-SRF6-KD and MBP-HAE-KD are 86.5 kD and 80.5 kD, respectively. A K711E substitution in HAE-KD leads to defective kinase activity, while the corresponding substitution of lysine with glutamic acid in SRF6-KD occurs at position K444E. (b) Phosphoproteins were detected using Pro-Q Diamond staining (top), while total proteins were visualized with Coomassie Brilliant Blue staining (bottom). HAE-KD, a well-known autophosphorylating protein kinase, and HAE-K711E, a kinase-dead variant, were used as references. (Taylor et al., 2013). Asterisks (*) indicate MBP-SRF6-KD and MBP-HAE-KD. Figure 5. Transcriptional memory analysis of SRF6 . (a) The control (CK), heat-primed (P), heat-triggered (T), and combined heat-primed and heat-triggered (P+T) regimes are shown in the diagram. (b) The expression patterns of SRF6 , AZF3 , and HSP18.2 in the CK, P, T, and P+T conditions were analyzed. Data are presented as mean ± SD (n = 3). qRT-PCR assays were performed in triplicate, and significant differences are indicated by different lowercase letters (ANOVA, Tukey-Kramer test, P 2], served as a positive control, while HSP18.2 was used as a reference gene. PP2A was used as an input control. Figure 6. Thermotolerance tests of the srf6-1 mutant. Seven-day-old seedlings were assayed for basal thermotolerance (BT), short-term acquired thermotolerance (SAT), long-term acquired thermotolerance (LAT), and gradient heat stress (GHS), as illustrated in each panel. (a) For BT, seedlings were exposed to 44°C for 21–23 min and allowed to recover for 10 days. (b) For SAT, seedlings were pretreated at 37°C for 1 h, recovered for 2 h, then exposed to 44°C for 155–165 min, followed by 10 days of recovery. (c) For LAT, seedlings were pretreated at 37°C for 1 h, recovered for 2 days, and then challenged at 44°C for 70–80 min, followed by 10 days of recovery. (d) For GHS, seedlings were gradually heated from 22–44°C over 6 h at 3°C per hour, then exposed to 44°C for 160–180 min, and recovered for 10 days. Seedlings were photographed, and the survival rate (%) of Col, srf6-1 , and hsp101 was assessed 10 days after heat treatment. Data are presented as mean ± SD (n = 4), with significant differences indicated by different lowercase letters (ANOVA, Tukey-Kramer test, P < 0.05). Figure 7. Thermotolerance test of lines overexpressing the SRF6-3xFLAG transgene in both srf6-1 and Col backgrounds. Seven-day-old Col and SRF6 -OE lines, which contain the 35S::SRF6-3xFLAG transgene in the Col background ( SRF6 -OE/Col) and the srf6-1 background ( SRF6 -OE/ srf6-1 ), were analyzed. (a) and (b) Transgene expression was assessed by immunoblotting with an α-FLAG antibody and by qRT-PCR, respectively. Ponceau S-stained blots showed that the ribulose bisphosphate carboxylase large subunit (RbcL) served as an input control. The molecular weight of SRF6-3xFLAG is 81 kD. (c) The pictogram shows the HS regime. Seven-day-old seedlings were pre-treated at 37°C for 1 h, allowed to recover for 2 h, then exposed to 44°C for 160 min, followed by 10 days of recovery. Seedlings were photographed, and the survival rate (%) was assessed 10 days after heat treatment. Data are presented as mean ± SD (n = 3). Statistically significant differences between each line are indicated by different lowercase letters (ANOVA, Tukey-Kramer test, P < 0.05). Figure 8. Expression levels of stress-responsive genes in the srf6 mutant under heat stress. Seven-day-old Col and srf6-1 seedlings were maintained under normal conditions (CK) or exposed to heat stress (HS) at 37°C for 1 h (HS1h) or 3 h (HS3h), followed by recovery at 22°C for 1 h (R1h). The expression levels of (a) heat shock protein genes, HSP70 , HSP90 , HSP101 , and HSP22 , as well as CaM3 , a Ca 2+ -responsive gene; (b) ER stress-responsive genes, including Bip2 , bZIP28 , and both unspliced and spliced forms of bZIP60 ; (c) ABA-responsive genes AREB1 , AREB2 , RD29A , and RD29B ; and (d) ROS-responsive genes APX1 , APX2 , CAT1 , and RBOHD were analyzed by qRT-PCR. Expression levels were normalized to the Col control (CK). Data are presented as mean ± SD (n = 3). An asterisk (*) indicates significance at P < 0.05 (Student’s t test) compared to Col. PP2A was used as an input control. Figure 9. Proposed model of SRF6-mediated heat stress signaling and thermomemory. SRF6 acts downstream of HSFA1s and is regulated by HSFA7b. In srf6 mutants, the absence of SRF6 impairs heat-induced HSPs , leading to unfolded protein accumulation and activation of ER stress markers bZIP28/60 and Bip2 . ABA-responsive genes AREB1/2 and RD29A are downregulated, and ROS homeostasis is disrupted, compromising APX2 , CAT1 , and RBOHD , thereby affecting protein folding, cellular protection, and thermomemory. Collectively, SRF6 functions as a plasma membrane receptor-like kinase that links primary heat perception to downstream signaling, integrating thermosensory, hormonal, and redox pathways to sustain heat tolerance and recovery. Supplementary Information Supplementary Table 1. List of primer sequences for genotyping, cloning, and RT-qPCR. Supplementary Figure 1. Predicted cis -elements in the 2.0-kb promoter region of SRF6 . Supplementary Figure 2. Histochemical analysis of SRF6 promoter:: GUS plants. Supplementary Figure 3. Amino acid sequence of the cytoplasmic kinase domain (KD) of SRF6 and design of the MBP-SRF6-KD construct. Supplementary Figure 4. Genotyping and characterization of SRF6 T-DNA insertion lines. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Supplementary Material File (image8.png) Download 1.89 MB Information & Authors Information Version history V1 Version 1 02 February 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords heat shock response heat stress memory non-rd type rlk signaling thermotolerance Authors Affiliations Hsin-Ying Chang National Taiwan University Institute of Plant Biology View all articles by this author Chih-Chi Lai National Taiwan University Institute of Plant Biology View all articles by this author Ya-Chen Huang National Taiwan University Institute of Plant Biology View all articles by this author Hui-Chen Wu 0000-0002-4991-7616 National University of Tainan View all articles by this author Tsung-Luo Jinn 0000-0002-5185-7691 [email protected] National Taiwan University Institute of Plant Biology View all articles by this author Metrics & Citations Metrics Article Usage 172 views 59 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Hsin-Ying Chang, Chih-Chi Lai, Ya-Chen Huang, et al. SRF6, a Heat-Responsive Receptor-Like Kinase, Mediates Thermotolerance in Arabidopsis. Authorea . 02 February 2026. 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