Comparative Transcriptome Analysis of Resistant and Susceptible Genotypes of Isabgol (Plantago ovata) During Interactions with Peronospora plantaginis, the Causal Agent of Downy Mildew Disease

Downy mildew (DM) disease, caused by obligate oomycete Peronospora plantaginis Underwood, is the single most damaging disease affecting the yield and quality of isabgol (Plantago ovata Forsk). The infection leads to characteristic ash-colored downy growth, and as the disease progresses, leaf tissue turns yellowish due to loss of chlorophyll, ultimately reducing the effective photosynthetic area. However, reports on the molecular mechanisms mediating host plant resistance are still unknown. In the present study, we conducted a comparative transcriptome between the resistant and susceptible genotypes of isabgol in response to DM infection. We identified significantly differentially expressed genes (DEGs) genes: 6928 in control (RU) vs. infected (RI) of DPO-185 (resistant DM) and 8779 in control (SU) vs. infected (SI) of DPO-14 (susceptible to DM). Putative genes 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 58 candidate resistance (R) genes enriched in response to DM infection. The expression of 11 genes involved in plant defense quantified using RT-qPCR indicated a significant difference in the expression pattern. This study for the first time provides a glimpse of transcriptional responses to the DM resistance in isabgol which can guide investigating the molecular mechanisms associated with plant defense and to develop control mechanisms accordingly for DM disease.