Silicon mediates polyamine-induced inhibition of ethylene synthesis and regulates the expression of PpERF21 and PpERF27 to inhibit gummosis in peach

Silicon mediates polyamine-induced inhibition of ethylene synthesis and regulates the expression of PpERF21 and PpERF27 to inhibit gummosis in peach | 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 Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed.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. 31 January 2024 V1 Latest version Share on Silicon mediates polyamine-induced inhibition of ethylene synthesis and regulates the expression of PpERF21 and PpERF27 to inhibit gummosis in peach Authors : huaifeng gao 0000-0001-7137-9132 , Xuelian Wu , Xiaoqing Yang , Anqi Du , Jiahui Liang , Wenying Yu , Maoxiang Sun , Futian Peng [email protected] , and Yuansong Xiao Authors Info & Affiliations https://doi.org/10.22541/au.170670008.89472384/v1 255 views 120 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Gummosis in peach is an invasive disease that causes widespread and serious damage. Mechanical damage and ethylene (ETH) can induce gummosis in peach shoots in the field. In this study, we found that silicon can induce the synthesis of polyamines (PAs) and reduce the synthesis of ETH, thereby inhibiting gummosis in peach. The results showed that silicon (Si) can decrease the rate of gummosis, reduce the expression level of PpACS1 and reduce the enzyme activity of polygalacturonase (PG). Simultaneously, the expression level of PpSAMDC and the PAs content were increased and the ETH synthesis rate was decreased. Si inhibits the synthesis of ETH by promoting PAs synthesis. It was further discovered that Si can regulate the gene expression of PpERF21 and PpERF27 . Yeast one-hybrid and dual-luciferase reporter assays showed that PpERF21 and PpERF27 , through direct interaction with the promoter of PpPG1 , inhibited the transcriptional activation of PpPG1 . Overexpression of PpERF21 and PpERF27 effectively reduced fruit colloid production when bacterial cells harbouring the expression vector were used to instantaneously infect peach fruit. These results show that Si can inhibit the synthesis of ETH by promoting PAs synthesis, mediating PpERF21 and PpERF27 expression to inhibit the expression of PpPG1 , thereby inhibiting gummosis in peach. Introduction: Silicon (Si) is abundant in the Earth’s crust and is the second most abundant element in the soil after oxygen. Si is also an important component of plants and is present in most plant tissues; it has been shown to be beneficial in improving plant tolerance to biotic and abiotic stresses. Under drought conditions, the relative water content, water potential and growth of rice treated with Si were higher than those without Si treatment. And Si can change the structure of wheat leaves and reduce transpiration, thus enhancing the drought resistance of wheat (Gong et al., 2003). It was found that Si increased the levels of polyamines (PAs), such as free and bound putrescine (Put), in sorghum tissues under salt stress, and the expression of genes (ADC, CAP, SAMDC) related to the synthesis of PAs was enhanced; it also reduced the accumulation of Na+, so the salt tolerance of sorghum was enhanced (Chen et al., 2016). Gummosis is the process of accumulation and exudation of gum or sap in the trunks, branches, and fruits of some plant species (Li et al., 2015). Gummosis in peach occurs mostly in the main branches, the bark of peach trees has lesions before the onset of gummosis, and this part becomes swollen. Then, a translucent gum containing a variety of polysaccharides is secreted. The gum gradually turns into a brown hard rubber block when it is exposed to air after it flows out. As more gum flows out, the tree experiences severe nutrient loss, and some of the gum that flows out become dry and starts to rot; the health of the branches declines until the whole plant is dead (Sun, 2019). Gummosis in peach trees occurs via a series of complex physiological and biochemical reaction processes after stress. Pest-induced wounds, mechanical damage, frostbite, burns and other stress injuries can induce gummosis in peach. The main components of the plant cell wall are polysaccharides, including pectin, xylose, cellulose, hemicellulose, gum arabic, and galactose (Sonja et al., 2004); the main additional components of peach gum polysaccharides are arabinose, galactose, xylose, and glucuronic acid-like substances (Simastosin et al., 2009). Peach gum has polysaccharides similar to those of the cell wall. Studies have shown that peach gum is produced by the disintegration of parenchyma cells near the pericarp and vascular cambium, and cell wall degradation is a prerequisite condition for the formation of resin tubes (Li et al., 2014). Therefore, the formation of both gum and resin tubes are closely linked with degradation of the cell wall and the activities of cell wall-degrading enzymes. There are many kinds of cell wall-degrading enzymes, among which pectin methylesterase (PME), polygalacturonase (PG) and β-galactosidase (β-Gal) are closely related to gummosis in peach. As a plant hormone, ethylene (ETH) has important physiological effects. ETH is synthesized from methionine (methionine, Met), and the immediate precursor of ETH is 1-aminocyclopropane-1-carboxylic acid (ACC). ACC synthase (ACS) and ACC oxidase (ACO) are two key enzymes involved in ETH synthesis. ACS catalyses the synthesis of ACC from S-adenosylmethionine (SAM), which exists in the cytoplasm; SAM is present at extremely low levels and is unstable and easily degraded. A study showed that a high endogenous ETH content is the key factor involved in gummosis (Wei et al, 2016). ETH or ethephon can promote the formation of gum, and this effect is related to the direct action of ETH on the gum to stimulate its formation (Saniewski et al., 2006). Research has shown that Si can mediate the drought resistance of sorghum by inhibiting the synthesis of the ETH precursor ACC and can improve the antioxidant capacity of plants. PAs are essentially aliphatic compounds that have multiple functions in plant growth and development and act on cell homeostasis (Leonardo et al., 2010; Bregoli et al., 2006). They are involved in protective stress responses, and under conditions of increased stress, the level of PA biosynthesis is significantly increased (Franchin et al., 2007). SAM is catalytically decarboxylated by SAM decarboxylase (SAMDC). In addition to serving as a methyl donor, decarboxylated SAM is also a common precursor for the synthesis of PAs and ETH, so SAMDC is considered to be a regulator of two synthetic pathways. Si was shown to enhance the expression of the SAMDC gene, encoding a key enzyme in the biosynthesis of PAs, thereby promoting PAs synthesis and inhibiting ETH synthesis (Yin et al., 2016). To better explore the phenomenon of gummosis suppression by Si in peach, we studied the factors that influence the inhibition of gummosis by Si. Through a series of experiments, we found that PAs and ETH are involved in the process of Si-mediated gummosis in peach. Materials and methods Treatment of peach shoots and fruit with Si Throughout the experiments, shoots were collected from 3-year-old Prunus persica (L.) ‘Spring snow’ plants. The plants were grafted onto wild peach rootstocks, and the plants were grown in the experimental field of Shandong Agricultural University in Taian. The isolated shoot segments were cultured in an incubator with humidity >70% at 35°C and a 12 h light (20,000 lux) photoperiod, and temperature treatments were performed in the incubator. The shoots were cut into 12-cm-long segments and surface-sterilized with 75% alcohol for 10 s, followed by rinsing three times with sterile water. The shoot segments were wounded at intervals of 0.5 cm from the midpoint using a sterilized needle, and then, 2% ethephon was sprayed on the shoot segments, which were then stored in a closed plastic container for 30 minutes. Treatments with Si and various inhibitors were performed as follows: Si and the various inhibitors (0.6 mmol/L Na 2 SiO 3 , 0.5 mmol/L AgNO 3 , 0.6 mmol/L CoCl 2 , 50 mg/L ACC, 10 mg/L D-arginine (D-Arg), 0.5 mmol/L methylglyoxal bis (guanylhydrazone) (MGBG), 0.5 mmol/L aminoethoxyvinylglycine (AVG), 0.1 mmol/L Put, 0.1 mmol/L spermidine (Spd), 0.1 mmol/L spermine (Spm) were applied individually or together on selected peach shoots, and water was sprayed on the branches as a control. Each sample consisted of tissue from 30 peach segments, and six independent samples were taken from the treated and control segments in the same manner. The treatment was continued for 4 days. Samples were taken at 0 h, 6 h, 1 day, 2 days and 4 days after treatment, and the tissue within 0.5-1.0 cm from the wound point was collected from the segments. The peach fruit were treated differently from the branches. After disinfection, the fruit were punctured at intervals of 0.5 cm and cultured aseptically after treatment with different reagents. The samples were promptly frozen in liquid nitrogen and then kept at a temperature of -80°C for later use. Homeopathic infestation of peach fruit Eighteen peach fruit were completely immersed in 75% alcohol for 5 minutes and rinsed with sterile water three times. The surface was dried with filter paper on an ultraclean workbench, and the surface of the fruit was punctured evenly at 0.5 cm intervals. An overexpression vector containing the gene of interest was used to transform bacterial cells, which were cultured with 10 mM 2-(N-morpholino)-ethanesulfonic acid (MES), 10 mM MgCl2, and 150 µM acetosyringone at pH 5.6, and the bacterial concentration was adjusted to OD600=0.6~0.7. The empty plasmid was used as a negative control. The peach fruit were immersed in the bacterial culture, vacuum infiltrated at 0.7 MPa for 30 minutes, washed with sterile water 3 times, and cultured for 7 days. The sterilized fruit were symmetrically cut into 4 pieces of 1-cm-thick peach pulp and inoculated in MS medium for 24 h. After culturing for 24 h, the peach pulp was immersed in the bacterial culture, vacuum infiltrated at 0.7 MPa for 30 minutes, washed with sterile water 3 times, inoculated in MS medium and cultivated for 3 days (Liu et al 2017). The infected peach pulp was frozen in liquid nitrogen and stored in a freezer at -80°C for later use. Measurement of ethylene production At different time points, 6 stems or 3 fruit subjected to different treatments were selected and cultivated in a closed beaker for 3 h. One millilitre of gas from the beaker’s headspace was sampled after incubation. A gas chromatograph (GC-2014C, Shimadzu, Japan) equipped with a GDX-502 column and a flame ionization detector was used to measure ETH production (FID). The injection temperature was 120°C, and the column temperature was 70°C. N 2 was used as the carrier gas at a rate of 40 mL min -1 . The rate of ETH production was expressed as nL C2H4 h -1 kg -1 FW. ACC measurement Two millilitres of 85% ethanol was used to extract 0.5 g (fresh weight) of plant material. Following drying of the extracted supernatant, 1 mL of chloroform and 1 mL of distilled water were added separately. Then, HgCl 2 and NaOCl/saturated NaOH (2:1) were added to the aqueous phase. After incubation and intermittent agitation, 1 mL of the air in the headspace was extracted with a gas syringe and injected into a gas chromatograph (GC-2014C, Shimadzu, Japan). The aqueous phase was hydrolysed in 6 M HCl at 100°C for 3h to quantify malonyl-ACC (MACC, conjugated ACC). The amount of MACC was computed by subtracting the quantity of free ACC from that of total ACC. PA quantification High-performance liquid chromatography was used to examine the PA content (HPLC: LC-1290, Agilent, America). Plant materials (1 g) were pulverized and homogenized in 5 mL of 5% HClO4 and extracted overnight at room temperature on a shaker. The collected supernatant was used to determine the amount of free PAs after centrifugation. To measure the bound PAs (conjugated PAs and macromolecules), the residue of the plant extract was washed with 5% HClO4 and then hydrolysed in 6M HCl at 110°C for 15 h. The filtered hydrolysate was evaporated to dryness, and the residue was dissolved in 5% HClO4 for quantification of the bound PAs. RNA extraction and quantitative PCR According to the manufacturer’s instructions, an RNAprep Pure Plant Kit (Tiangen, Beijing, China) was used to isolate total RNA from 0.5 g of samples. The PrimeScriptTM RT Kit (Takara, Japan) was used to generate first-strand cDNA according to the manufacturer’s instructions. On a QuantStudio® 3 real-time PCR instrument (Thermo, USA), we performed three biological and three technical duplicate RT-qPCRs using SYBR® Premix Ex TaqTM (Takara, Japan), with PpActin as the reference gene, according to the manufacturer’s recommendations for all reagents. The 2 −ΔΔCT approach was used to calculate the relative expression levels (Schmittgen and Livak, 2008). SPSS Statistics v. 20 was used to analyse the data. Subcellular localization of PpERF21 and PpERF27 For subcellular localization detection, the cDNA sequences of PpERF21 and PpERF27 were amplified without the stop codon and ligated into the pCAMBIA1300-GFP (35S::GFP) vector. As previously stated, Agrobacterium GV3101-infected tobacco epidermal cells with the PpERF21 -GFP, PpERF27 -GFP, and control GFP constructs were obtained. The GFP fluorescence signal from the transformed epidermal cells was detected using a Zeiss LSM880 microscope after 3 days of culture, and the images were processed using the ZEN lite program (Zeiss). Yeast one-hybrid assays To create the bait plasmid PpPG1 -pHIS2, the PpPG1 promoter fragment was ligated into the pHIS2 vector, and the promoter fragment included the original DNA replication-related element (DRE). The plasmid was transferred into the yeast strain Y187, and the lowest dose of 3-amino-1,2,4-triazole (3AT) that completely inhibited the growth of the bait yeast strain was determined. The cDNAs of PpERF21 and PpERF27 were cloned into the pGADT7 vector, and the two plasmids were cotransformed into the yeast strain Y187 and cultured on SD/-Leu plates to assess the interactions among PpERF21 , PpERF27 , and PpPG1 -pHIS2 at 28°C for three to five days. Empty pGADT7 vector was employed as a negative control. Dual-luciferase reporter assay Dual-luciferase (dual-luc) detection was performed as stated above (Wang et al., 2020). The full-length cDNAs of PpERF21 and PpERF27 were inserted into the pGreenII 0029 62 SK vector to generate effector constructs. The PpPG1 promoter fragments were cloned into the pGreenII 0800 LUC vector to generate reporter constructs. Mycobacterium tuberculosis GV3101 was used to generate all of the recombinants. A mixture of Agrobacterium strains was used to infect ’tobacco leaves. An in vivo imaging system (IVIS Lumina II, Xenogen, Alameda, CA, USA) was employed for fluorescence detection. Results 1. Effects of different concentrations of Si on gum formation, ethylene synthesis and cell structure in wounded peach segments Fig 1. Rates of gum formation and ethylene synthesis. Note: a. Photograph of wounded shoot segments. b. Gum formation score. c. Ethylene synthesis rate. d. Electron microscopy image of the cell structure treatment with water；e. Electron microscopy image of the cell structure treatment with 0.6mmol/L Si.Different concentrations of Si were applied to the wounded shoot segments. Gum formation was observed visually, and the relative amounts were scored as follows: − no gum; + to ++++, increasing degrees (amounts) of gum production (+, trace; ++++, high). The concentrations of Si used were 0.6 mmol/L, 1.2 mmol/L, and 1.8 mmol/L. The gum formation and ETH synthesis rates were investigated in wounded peach segments treated with Si. Following Si treatment, the rate of gum formation decreased, as shown in Fig 1a. A similar result was observed for ETH synthesis in the treated peach segments (Fig 1c). After 12 h of Si treatment, ETH production has decreased and was significantly lower than that in the control. Electron microscopy further showed that Si inhibited cell wall degradation (Fig 1d and 1e). After Si treatment, the cell integrity improved, and the intracellular structure did not change significantly, no obvious breaks in the cell wall, indicating preservation of cell integrity or alleviation of stress damage. 2. Effects of Si on gum formation and ethylene synthesis in wounded peach segments Fig 2. Rates of gum formation and ethylene synthesis, Si content, enzyme activity and relative expression of ACS and ACO. Note: a. Photograph of the wounded shoot segments. b. Si content. C. Ethylene synthesis rate. d. Enzyme activity of ACS. e. Enzyme activity of ACO. f. Relative expression of PpACS1 . g. Relative expression of PpACS2 . h. Relative expression of PpACO . To better understand the effect of Si on gum formation, CoCl2 (an ETH synthesis inhibitor) and AgNO3 (an ETH receptor inhibitor) were used. As shown in Fig 2a, gummosis was observed after different treatments, but the shoot segments treated with these two inhibitors and Si exhibited considerably reduced gummosis. The same trend was observed for ETH production (Fig 2c). Si could reduce gum formation and ETH synthesis but increase the Si content in the peach segments (Fig 2b). To prove that ETH synthesis can be reduced by Si, both the key enzyme activity and the relative expression levels of genes involved in ETH synthesis were determined. Under Si treatment, the enzyme activity (Fig 2d) and relative expression levels of PpACS1 (Fig 2f) and PpACS2 (Fig2g) showed an decrease. Si showed exhibited the same effects as the ETH synthesis inhibitor CoCl2. PpACS1 is a key gene in ETH synthesis in peach, and the change in the relative expression of this gene directly proves that Si has an inhibitory effect on ETH synthesis. Under the same experimental conditions, PpACO did not show the same results as PpACS1 (Fig2h). 3. Effects of Si on the ACC content Fig 3. Rates of gum formation and ethylene synthesis and the ACC content. Note: a. Photograph of the wounded shoot segments. b. Ethylene synthesis rate. c. Total ACC content. D. Free-ACC content. The results showed that Si affected the enzyme activity of ACS during ETH synthesis, and the activity of ACS affected the ACC content. We hypothesized that ACC might play a role in the effect of Si on gummosis, so ACC treatment was performed. The results showed that the inhibition of Si to gummosis was weakened after ACC treatment; Si reduced the levels of free ACC and total ACC in peach segments(Fig 3c and 3d), and the gum formation and ETH production trends were the same as that of the ACC content, After using ACC, their production rate increases and the inhibitory effect of Si is alleviated (Fig3a and 3b). 4. Effects of PAs on ethylene synthesis in peach segments Fig 4. Rates of gum formation and ethylene synthesis, ACC content, enzyme activity and relative expression of ACS. Note: a. Photograph of the wounded shoot segments. b, Ethylene synthesis rate. c. Total ACC content. D. Free-ACC content. e. Enzyme activity of ACS. F. Relative expression of PpACS1 . g. Relative expression of PpACS2 . To investigate the effect of PAs on ETH synthesis, Put, Spd, Spm and D-Arg (Putrescine synthesis inhibitor) were used. As shown in Fig 4a and Fig 4b, Spd and Spm inhibited gum formation and ETH synthesis, and Si showed the same effect. Put did not show a significant inhibitory effect on ethylene synthesis, and when his synthesis was inhibited, it did not significantly affect the peach segments (Fig 4b). To further clarify the effect of PAs on ETH synthesis, the activity and expression of ACS and the ACC content were determined. The total ACC and free-ACC levels were reduced by Spd and Spm, and were the same as those under Si treatment (Fig 4c and Fig 4d). The enzyme activity results showed that Si, Spd and Spm could inhibit the activity of ACS (Fig 4e), and the relative expression of PpACS1 controlled by them, its expression is suppressed by Si, Spd and Spm, but the relative expression of PpACS2 did not conform to this trend. 5. Effect of Si on the synthesis of PAs and ethylene Fig 5. Ethylene synthesis rate, ACC content, PA content, enzyme activity and relative expression of ACS and SAMDC. Note: a. Ethylene synthesis rate. b. Total ACC content. c. Free-ACC content. d. Enzyme activity of ACS. d. Enzyme activity of SAMDC. f. Relative expression of PpSAMDC . g. Relative expression of PpACS1 . h. Relative expression of PpACS2 . i. Put content. j. Spd content. k. Spm content. The ETH and PA synthesis pathways are considered to be in competition with each other because they share the same precursor, methionine. Under AVG (an ACC synthesis inhibitor) and MGBG (an Spd and Spm synthesis inhibitor) treatment, the synthesis of ETH and PAs showed opposite trends (Fig 5a); AVG inhibited the synthesis of ACC and promoted the synthesis of Spm and Spm, while MGBG had the opposite effect (Fig 5b and Fig 5c). Si alone inhibited ACC synthesis and promoted PA synthesis, but this effect disappeared when peach segments were treated with Si mixed with MGBG (Fig 5b and Fig 5c). We examined the enzyme activity and expression levels of genes involved in PA and ACC synthesis in peach segments and found that Si increased the activity of PA synthase but inhibited ACS activity (Fig 5d and Fig 5e). The expression of PpACS1 , as an important ACC synthesis gene involved in peach, was inhibited by Si, but this effect was weakened when MGBG was added (Fig 5g). Si enhanced the expression of the SAMDC gene, and this effect was enhanced by AVG (Fig 5f). And the synthesis of polyamines is also obviously affected by them. Si and AVG increase the content of PAs in peach segments, and the promotion of their synthesis by Si is weakened by MGBG (Fig 5i, 5j and 5k). This series of results show that Si inhibits the synthesis of ACC by promoting the synthesis of Spm and Spd, thereby inhibiting the production of ethylene. 6. Effect of Si on ethylene synthesis in peach fruit Fig 6. Ethylene synthesis rate, ACC content, enzyme activity and relative expression of ACS and SAMDC. Note: a. Photograph of the wounded peach fruit. b. Enzyme activity of β-Gal. c. Enzyme activity of PME. d. Enzyme activity of PG. e. Relative expression of PpGAL . f. Relative expression of PpPME . g. Relative expression of PpPG1 . h. Ethylene synthesis rate. i. Relative expression of PpPG1 . j. Enzyme activity of PG. Peach fruit can produce large amounts of ETH. To further verify the inhibition of ETH synthesis by Si, we repeated the experiment with flat peach fruit. The results showed that ETH synthesis decreased under Si treatment, and gum flow from the fruit was significantly inhibited by Si (Fig 6a and 6h). The inhibition of Si to gum flow was the same as that induced by cobalt chloride, an inhibitor of ETH synthesis. Gummosis is closely related to cell wall degradation. We used an enzyme-linked immunosorbent assay kit and quantitative RT–PCR to examine the enzyme activity and expression of β-Gal ( EF568777 ), PME ( ppa003578m ) and PG ( PG1 , ppa007271m ). The results showed that after Si treatment, the activities of these three enzymes were inhibited, especially after 24 h, when their expression levels were much lower than those in the control treatments, among them, the enzyme activity and expression of PG are most affected by Si (Fig 6b-6g). These results combine with those of previous studies indicate that cell wall degrading enzyme especially PG may play a prominent role in this process. The enzyme activity of PG and the relative expression level of PpPG1 were increased by ethephon and inhibited by 1-methylcyclopropene (1-MCP) (Fig 6i and 6j), indicating that Si can mediate the ETH-induced inhibition of PG activity. 7. Differential expression of ERF genes Fig 7. Differential expression of ERF genes. Note: a. Differential expression of ERF genes. b. Relative expression of ERF genes. c. Subcellular localization of PpERF21 and PpERF27 . Using differential gene expression (DGE) analysis, we found significant changes in the gene expression of 13 ERF transcription factors, and the results were verified by quantitative RT–PCR (Fig 7a and 7b). As shown, under Si treatment, ten of these genes were upregulated, and three were downregulated. Among them, the relative expression of PpERF21 and PpERF27 showed the most significant change, and subcellular localization analysis showed that PpERF21 and PpERF27 could be expressed both in the nucleus and at the cell membrane (Fig 7c). These genes are regulated by Si and we use them for the next step of research. 8. PpERF21 and PpERF27 directly interact with the promoter of PpPG1 Fig 8. PpERF21 and PpERF27 directly interact with the promoter of PpPG1 . Note: a. Schematic diagram of the bait fragment. b. Results of the yeast one-hybrid experiment. c. Dual-luciferase reporter assay. According to bioinformatic analysis, the DRE motifs to which ERF transcription factors can bind (positions –508 to –504 relative to the translational start site) were detected in the promoter of PpPG1 but not in PpACS1 (Fig 8a). Yeast one-hybrid assays showed that when the concentration of 3AT was 0 mmol/L, the yeast strain containing the PpPG1 promoter grew normally on SD/-Leu medium after transformation with pGADT7- PpERF21 , pGADT7- PpERF27 or empty vector. When the 3AT concentration was 25 mmol/L or 50 mmol/L, only the yeast strain that was transformed with the pGADT7- PpERF21 and pGADT7- PpERF27 plasmids grew normally on SD/-Leu medium, while the growth of the yeast strain that was transformed with empty pGADT7 plasmid was severely inhibited. The results showed that PpERF21 and PpERF27 could bind to the promoter of PpPG1 but could not interact with PpACS1 (Fig 8b). To validate the transcriptional activity, a dual-luc reporter assay was performed. PpERF21 and PpERF27 cDNAs were cloned and coupled to the pGreenII 62-SK vector. Luminescence detection revealed that coexpression of Pgreen-62SK- PpERF21 with Pgreen-0800Ⅱ- PpPG1 led to markedly weaker luminescence intensity than that obtained with the expression of Pgreen-62SK-Empty with Pgreen-0800Ⅱ- PpPG1 . These results indicated that PpERF21 directly interacts with the promoter of PpPG1 and inhibits the transcriptional activation of PpPG1 (Fig 8c). PpERF27 showed the same effects as PpERF21 . 9. PpERF21 and PpERF27 could inhibit the expression of the PpPG1 gene Fig 9. Homeopathic infestation of peach fruit. Note: a. Photograph of the wounded peach fruit. b. Photograph of flesh infected by homeopathy: (a) control; (b) pCAMBIA-Empty; (c) pCAMBIA1300- PpERF21 ; (d) pCAMBIA1300- PpERF27 . c. Relative expression of PpERF21 . d. Relative expression of PpERF27 . e. Relative expression of PpPG1 . To study the effects of PpERF21 and PpERF27 on the PpPG1 gene promoter in peach fruit, we constructed the pCAMBIA1300- PpERF21 and pCAMBIA1300- PpERF27 overexpression vectors that carried a GFP label. Overexpression of PpERF21 and PpERF27 effectively reduced fruit gums production when bacterial cells containing the expression vector were used to instantaneously infect flat peach fruit (Fig 9a). The pulp was infected with bacterial cells containing the expression vector and cultured in MS medium for 3 days, and GFP fluorescence was used for detection. The results showed that the pulp infected with empty vector and the PpERF21 or PpERF27 vector emitted fluorescence, while the pulp infected with MMA did not, indicating that the vector successfully entered the flesh and was expressed (Fig 9b). The gene expression of PpERF21 , PpERF27 and PpPG1 was detected by RT–qPCR. Compared with the no-load negative control, the expression levels of the genes PpERF21 and PpERF27 were significantly increased, indicating that the gene had been successfully transferred into the cells, and the expression levels of the genes PpPG1 is significantly suppressed (Fig 9c). The result showed PpERF21 and PpERF27 could significantly inhibit the expression of the gene PpPG1 in transiently transformed peach flesh. DISCUSSION Gummosis is a disease that is considered to involve a series of physiological and biochemical reactions that are part of a complex stress response (Li et al.,2015). Many factors, such as insect wounds, mechanical damage, frostbite, burns and other stress injuries, induce gummosis in peach trees. Colloid formation is often accompanied by cell wall degradation. By radiolabelling the polysaccharides from the cell wall of the epithelial cells of the resin tube in cherry trees, it was found that the gel was derived from the polysaccharides in the cell wall and that the colloid formed by these polysaccharides was a product of cell wall degradation (Vincent et al.,2010; Li et al., 2014). Plant growth and resilience to biotic and abiotic stressors, such as drought, heat, salinity, heavy metal toxicity, pathogen infections, and arthropod herbivory, are typically enhanced by the deposition of Si in plant tissues. (Reinaldo et al.,.2020). In the preliminary observation of peach segments, we found that Si could reduce gum formation and inhibit cell wall degradation, protecting the internal structure of the cell. The Si content of peach segments increased significantly, indicating that Si had accumulated in the branches. Cell wall degradation is the basis of gummosis, and cell wall degradation enzymes play an important role in this process. The experiments showed that the expression levels of PME, PG and β-Gal changed significantly during gummosis in peach segments, especially that of PG, which changed by many orders of magnitudes and was clearly regulated by Si. PG plays an important role in cell wall structure changes and can participate in the decomposition of pectin, which leads to disintegration of the cell wall structure. Studies have shown that enhanced PG activity leads to the decomposition of pectin, which has a good correlation with the softening process of various fruits (Wang et al., 2017; Tadiello et al., 2016). The activity of cell wall-degrading enzymes is induced and regulated by ETH (Violeta et al., 2019; Rinaldo et al., 2011). Since ETH can increase the permeability of the plasma membrane of fruit cells, the extravasation of hydrolytic enzymes, and respiration and can provide energy for the synthesis of macromolecules such as cell wall enzymes, it is thought to be involved in the transcription and translation processes of cell (Alexander et al., 2002; Hiwasa et al., 2003; Kou et al., 2004). Therefore, Si has a significant inhibitory effect on the activity of cell wall-degrading enzymes by inhibiting the synthesis of ETH. ETH is widely present in various organs of plants, and the ETH content varies significantly in different organs at different times. Under adverse conditions, such as drought, low temperature, and mechanical damage, ETH can also produce stress and participate in the regulation of the plant defence process (Bram et al., 2014; Nunez-Pastrana et al., 2011). Studies have shown that the root cause of gummosis in peach is high endogenous ETH content (Zhu et al., 2011). ETH was applied to apricot and peach trees susceptible to gummosis, and it was found that ETH or ethephon could promote colloid formation. This effect was related to ETH acting directly on colloids and stimulating the formation of colloids. ETH plays a dual role in the regulation of plant diseases (Saniewski et al.，2006). On the one hand, ETH can induce the development of a defence mechanism in plants under stress and improve their resistance. On the other hand, increased ETH levels can accelerate the ageing process, making plants more susceptible to disease (Marta et al., 2020). Under Si treatment, ETH production in the treated peach shoots and fruit was significantly suppressed. These results indicated that Si inhibited the massive synthesis of ETH and weakens the negative effects of excessive ETH, it can still be used as a signal to induce a defence response in plants. Further experiments showed that Si affected the ACC content available for ETH synthesis, and this effect was weakened after the addition of AVG, indicating that Si played a role by inhibiting ACC synthesis. The total ACC content and free-ACC content in peach stem segments and fruit also support this conclusion. PAs are aliphatic compounds that play a variety of roles in plant growth and development, as well as cell homeostasis (Pottosin et al., 2014; Nader et al.,2020; Bregoli et al., 2006). PA biosynthesis levels are dramatically enhanced under increased stress and are involved in stress defence responses (Ashraf et al., 2011;Takahashi et al., 2009; Franchin et al., 2007). In this study, the PA levels increased with Si application, and Si increased the synthesis of Spd and Spm by upregulating the expression of SAMDC and increasing the activity of SAMDC (Yin et al., 2016; Ding et al., 2015). This conclusion was verified when MGBG and Si were used together and the increase in SAMDC expression and activity was reduced. SAMDC has a short half-life and is a rate-limiting enzyme in the production of Spd and Spm; overexpression of SAMDC increases PA levels and strengthens resistance. (Roy & Wu 2002). PAs working as stress signalling regulators can induce plant defence responses and enhance resistance (Kuznetsov et al., 2010; Kasukabe et al., 2004; Singh et al., 2015). Si increases the PA content, and this may also be a mechanism to inhibit the occurrence of gummosis. PAs may be involved in silica precipitation. Long-chain PAs were discovered to be involved in the mediation of silica precipitation from a silicic acid solution in diatoms (Kröger et al., 2000; Shi et al., 2013). This interaction between Si and PAs would have a beneficial effect on the precipitation of Si on the cell wall and induce plant defence responses. SAM is a precursor for ETH synthesis as well as a substrate for PA biosynthesis. The enzyme ACS catalyses the conversion of SAM to ACC, which is a critical regulatory step in the biosynthesis of ETH (Smadar et al., 2012). Further research found that PAs and ETH have opposite functions: ETH is a pro-senescence, proripening regulator, while PAs are progrowth, anti-senescence regulators, and they inhibit each other (Smadar et al., 2012). Si increased the Spd and Spm levels in peach stems, and qRT–PCR showed that the expression of SAMDC was upregulated. Furthermore, Spd and Spm inhibited ETH synthesis by reducing the enzyme activity of ACS and the gene expression of ACS, and the levels of total ACC and free ACC were decreased. This led us to wonder whether Si inhibits ETH synthesis through the PA pathway. Therefore, we introduced the ETH synthesis inhibitor AVG and the PA synthesis inhibitor MGBG and found that they had opposite effects. However, when Si and MGBG were used together, the synthesis of Spd and Spm was blocked, and the inhibitory effect of Si on ACC synthesis was weakened. The results for the enzyme activity and relative gene expression of ACS and SAMDC supported this conclusion. Overall, Spd and Spm exhibited a function similar to that of Si, while MGBG showed the opposite effect. ETH and PAs have a competitive interaction, implying that Si inhibits the synthesis of ACC by promoting the synthesis of Spd and Spm, thus inhibiting ETH synthesis. Decreased ACC accumulation, as well as ETH, can alleviate gummosis. The ERF gene family, one of the largest gene families in plants, is composed of transcription factor genes that have been studied in a variety of species, including plum ( Prunus mume ) and poplar ( Populus tremuloides ) (Du et al.,2013; Wang et al., 2016). ERF genes, which control the final steps in ETH signalling by binding to the GCC box in the promoter regions of PR genes, function in plant growth and development and in fruit ripening, as well as in various biotic and abiotic stress responses (Chung et al., 2010; Xie et al., 2014). Experiments have shown that fruit produce more ETH than branches, so transcriptomic analysis was performed on Si-treated fruit samples. The results showed that twelve ERF family members were regulated by Si, of which nine were upregulated and three were downregulated. We verified the relative expression levels of these genes by fluorescence quantification and then screened out PpERF21 and PpERF27 , which showed a large increase in relative expression levels treatment with Si, for further study. ERF proteins can bind to DNA cis-acting elements such as DRE (CCGAC), GCC box (AGCCGCC), (A/G)CC(G/C)AC, and AA(T)TTCAAA motifs through their conserved ERF domain. Many ETH-responsive genes include these elements in their promoters, indicating that ERFs are involved in ETH signalling or biosynthesis. (Wang et al.,2019). For example, tomato LeERF interacts with the GCC box and activates the expression of ETH biosynthesis genes. Apple ( Malus domestica ) MdERF2 interacts with the DRE motif in the promoter of the MdACS1 gene and suppresses its transcription, thereby inhibiting ETH biosynthesis in ripening fruit. We analysed the correlation between PpERF21 and PpERF27 and the promoters of PpACS1 and PpPG1 . Bioinformatic analysis revealed that PpERF21 and PpERF27 can directly bind to the promoter of PpPG1 but cannot bind to PpACS1 . Yeast one-hybrid assays showed that PpERF21 and PpERF27 could bind to the promoter of PpPG1 . This result was proven again when a dual-luciferase reporter assay was performed in tobacco and showed inhibition of the transcriptional activation of PpPG1 . To verify this conclusion, we constructed a PpERF21 and PpERF27 overexpression vector and infected fruit and flesh with bacterial culture. The expression of PpPG1 was significantly inhibited in flesh overexpressing PpERF21 or PpERF27 . All plant pathogens interact with plant cell walls and produce enzymes, such as PG, that degrade plant cell wall polysaccharides (Vorwerk et al., 2004). The inhibition of PpPG1 expression may have been the reason for the decrease in gummosis in fruit in the overexpression group. Studies conducted in rice have indicated that the physical barrier formed by Si accumulation increases plant resistance to diseases and insect pests. The accumulation of Si in the cuticle of plants creates a physical barrier, resulting in a double layer of Si in the cuticle that not only helps the plant resist pathogenic assaults but also improves the plant’s physical strength (Kim et al.，2011; Liang et al.，2015). It can alleviate the incidence of rice blast, and the Si content in rice stems is significantly negatively correlated with the disease index of rice blast (Detmann et al., 2012). After inoculation with rice blast, the ETH content in the Si treatment group was significantly lower than that in the control, which may be related to the mechanism by which Si alleviates rice blast (Ge et al., 2014). Si accumulation in wheat, as an elicitor of chemical defences, enhances resistance to aphids (Reinaldo et al., 2020). Therefore, Si can not only use physical means but also act as a chemical substance or signal substance to induce plant resistance (Mohammad et al.2020; Francois et al., 2005). In this study, Si mediated the PA-induced inhibition of ETH synthesis while simultaneously regulating the expression of ERF genes and inhibiting cell wall degradation, it’s also a manifestation of its use as a chemical substance or signal to enhance plant resistance. Elevated levels of plants damage and ETH have been reported under abiotic stress, such as salinity, drought, and wounding. In this study, ETH synthesis was significantly inhibited by Si compared with the control, suggesting a regulatory role of Si in traumatic stress-related processes. And suggest that Si may act as a signalling substance to induce continuous expression of the ERF gene (Sabine et al., 2019). Under Si treatment and wounding stress, ETH production was found to be lower than that in the control group, implying that the ETH content decreased under wounding stress, which led to interactions between and coregulation of genes involved in the plant defence system. These findings support the function of Si as an effective element for improving plant resilience to abiotic stressors, as shown in previous research (Coskun et al., 2019; Guntzer et al., 2012). Fig 10. Proposed model for the role of Si in inhibiting gummosis in peach. Note: Si can inhibit the synthesis of ethylene by promoting the synthesis of PAs, which regulate PpERF21 and PpERF27 to inhibit the expression of PpPG1 and thereby inhibit gummosis in peach. Induction of targets is represented by solid arrows, and inhibition is represented by blocked lines. The dashed arrow represents possible effects. 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Keywords erf ethylene gummosis hormones silicon Authors Affiliations huaifeng gao 0000-0001-7137-9132 Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Xuelian Wu Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Xiaoqing Yang Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Anqi Du Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Jiahui Liang Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Wenying Yu Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Maoxiang Sun Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Futian Peng [email protected] Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Yuansong Xiao Shandong Agricultural University College of Horticulture Science and Engineering View all articles by this author Metrics & Citations Metrics Article Usage 255 views 120 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation huaifeng gao, Xuelian Wu, Xiaoqing Yang, et al. Silicon mediates polyamine-induced inhibition of ethylene synthesis and regulates the expression of PpERF21 and PpERF27 to inhibit gummosis in peach. Authorea . 31 January 2024. DOI: https://doi.org/10.22541/au.170670008.89472384/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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