Research Projects

Rationale of the research: Rhizoctonia solani AG1-IA is the causal organism of the devastating sheath blight disease in rice, that causes up to 50% estimated annual yield loss under favourable conditions. The necrotrophic fungal pathogens such as R. solani, are known to establish infection in their host plant by primarily targeting the cell wall, which is composed of an intricate network of crystalline polysaccharides (cellulose, hemicellulose and pectin) and the aromatic polymer, lignin, together forming the recalcitrant lignocellulose. It serves as a protective barrier to several environmental stresses, particularly biotic stress such as pathogens (bacterial/fungal). Therefore, in order to overcome the recalcitrant lignocellulose, the pathogens secrete a plethora of cell wall-degrading enzymes, which are referred as Carbohydrate-Active enZymes (CAZymes). The CAZymes, acting in synergy, compromise the integrity of the plant cell wall, in turn facilitating invasion and colonization by the pathogen. Additionally, these enzymes induce necrosis, elicit plant immune responses, or generate damage-associated molecular patterns (DAMPs) during infection, therefore making them critical pathogenic determinants. Interestingly, the genome of R. solani AG1-IA encodes an arsenal of CAZymes, some of which are upregulated during different infection phases in rice as determined by transcriptomic analysis. However, a thorough understanding of majority of these CAZymes, such as their specific roles, biochemistry and degree of pathogenicity conferred, remain largely unknown. Hypothesis: The CAZymes of R. solani are not only catalytically efficient towards lignocellulose valorization, but are also critical pathogenic determinants, essential for infection of the host plant by R. solani. Objectives and key experiments: The proposed study aims at understanding the biochemistry of selected CAZymes that are upregulated during the different infection phases in rice. This will be primarily achieved by optimizing reaction parameters and conducting degradation studies with lignocellulosic substrates. Functional characterization of the selected CAZymes will be undertaken by gene silencing studies in order to understand their significance in pathogenesis of R. solani in rice. Additionally, the study also aims at determining the host (rice) proteins interacting with the CAZymes and establish the importance during infection process. This will be achieved by conducting Co-IP MS/MS analysis, while in planta interactions will be validated by BiFC assay. Significance: Taken together, the study will provide thorough understanding of the biochemical and functional characteristics of these less studied pathogenic determinants of R. solani AG1-IA. Moreover, as a part of future work, the CAZyme-interacting host proteins identified from this study, will be taken forward for functional modulation in rice using CRISPR-Cas9 based genome editing to impart sheath blight disease tolerance.