Transcriptional regulation of OsWRKY genes in response to individual and overlapped challenges of Magnaporthe oryzae and drought in indica genotypes of rice

Abstract

In rainfed rice cultivation, severe blast (Magnaporthe oryzae) infection is frequently observed following intermittent drought. We simulated the natural rainfed rice field and explored the complex transcriptional regulations behind enhanced susceptibility of rice towards blast disease. We identified eight new OsWRKY genes in the indica subspecies of rice using the updated v5.0 PlantTFDB and GRAMENE making it altogether 109 OsWRKY genes. Distribution of the OsWRKY genes in the 12 chromosomes of indica rice was uneven. Where, chromosome 1 houses maximum number of genes but chromosome 5 has the highest gene density. Motif analysis depicted presence of a new motif i.e., an autophagy protein 16 (ATG16) associated to group IIa of the OsWRKY genes. We selected twenty biotic stress-responsive OsWRKY genes to check their transcript accumulation pattern in individual and overlapping challenges of blast and drought in three indica rice cultivars viz., blast susceptible HR-12, and blast resistant Tetep (Pi54) and C101A51 (Pi2). Transcripts of most OsWRKY genes in the resistant cultivars accumulated early (6 h) and at higher levels compared to the susceptible check. Interestingly, a significant decrease in transcript accumulation of most of the blast responsive OsWRKY genes was observed in all the three cultivars when exposed to the overlapping challenges. Additionally, a significant reduction in biosynthesis of both the defense enzymes PAL and PO in blast and drought overlapped condition in the resistant cultivars indicated partial breakdown of resistance due to intermittent drought. To conclude, the present study has contributed to understanding of the relationship between the expression pattern of 20 biotic stress responsive OsWRKY genes in indica rice grown in rainfed condition coupled with intermittent drought and blast susceptibility.