Transcriptome profiling uncovers the involvement of CmXyn1, a glycosyl hydrolase 11, in Cochliobolus miyabeanus pathogenicity

Necrotrophic pathogen Cochliobolus miyabeanus (C. miyabeanus) causes rice brown leaf spot disease and drastically affects the yield and quality of rice grains. However, the molecular mechanism of rice-C. miyabeanus remains poorly understood due to the limited research conducted on this pathosystem. To elucidate the molecular mechanism of rice-C. miyabeanus, a transcriptome analysis was conducted from in vitro and in planta grown C. miyabeanus. This analysis led to the identification of a total of 24,060 genes of which 426 in vitro and 57 in planta expressed genes were predicted to encode for secretory proteins. As these 57 genes were specifically expressed in planta and were predicted to be secretory in nature, these were consider as putative effectors, highlighting their possible roles in the fungal pathogenicity. Notably, among these putative effectors, CmXyn1 which encodes a glycosyl hydrolase 11 displayed the highest expression level under in planta conditions and was thus selected for further functional characterization. Interestingly, the extracellular expression of CmXyn1 transiently induced cell death in Nicotiana benthamiana leaves, while intracellular expression was comparatively lesser effective. In addition, transcriptome analysis on rice leaves during C. miyabeanus infection and comparing it to the rice leaf transcriptome data obtained during hemibiotrophic pathogen Magnaporthe oryzae infection led to the discovery of 18 receptors/receptor-like kinases that were commonly expressed in response to both pathogens, indicating their key roles in rice defense response. Taken together, our findings provide new insights into rice-C. miyabeanus interaction as well as the unique and common defense responses of rice against hemibiotroph and necrotroph model systems.