Comparative Transcriptome Analysis Uncovers Genes and Pathways Relating to Downy Mildew Resistance in Isabgol (Plantago ovata Forsk.)

Background: Isabgol ( Plantago ovata Forsk.) downy mildew (DM), caused by obligate oomycete pathogen Peronospora plantaginis Underwood., is the single most damaging disease of Isabgol. However, reports on the genes and pathways involved in mediating resistance are still unknown. Results: In the present study, transcriptomic analysis was carried out by next generation sequencing of DM infected and uninfected leaves of resistant and susceptible genotypes to understand the genetic mechanisms underlie the host-plant resistance. A total of 33.47 million reads were generated and de novo assembled and annotated. The assembly using Trinity yielded 38803, 40175, 45451 and 39533 non-redundant transcript contigs, respectively in susceptible infected, Susceptible uninfected, Resistant infected and resistant uninfected samples. More than 90% of coding DNA sequence (CDS) predicted were annotated using BLAST search. Isabgol transcriptome showed the highest similarity to Sesamum indicum (41-59%) followed by Erythranthe guttata (10-13%). Putative CDS encoding Pathogen associated Molecular Pattern (PAMP)-triggered immunity (PTI), Effector-Triggered Immunity (ETI), Cell wall degrading enzymes, Phytohormone signalling and Phenylpropanoid biosynthesis pathways involved in host-pathogen interaction were identified in addition to the identification of several candidate resistance (R) genes enriched in response to DM infection. We identified significantly differentially expressed genes (DEGs) genes; 6928 DEGs in resistant uninfected (RU) vs resistant infected (RI) of DPO-185 (resistant) genotype and 8779 susceptible uninfected (SU) vs susceptible infected (SI) of DPO-14 (susceptible) genotype. Expression of 11 genes involved in plant defense quantified accordingly using RT-qPCR. Conclusions: This study for the first time provides the glimpse of transcriptional responses to the DM resistance in Isabgol. The genes and pathways will be helpful in further investigating the molecular mechanisms associated with DM disease resistance in Isabgol and to develop control mechanisms accordingly.