Fungal pathogens of plants cause tremendous yield losses in crop production worldwide. The molecular mechanisms underlying pathogen interference with host defenses have been gradually elucidated for plant bacterial and oomycete pathogens. However, these mechanisms are still poorly understood for fungal pathogens. Rice blast, caused by the fungus Magnaporthe oryzae, is the most devastating disease of rice. It serves as an advanced model pathosystem for researchers who study plant-fungal interactions in cereal crops. M. oryzae introduces an effector protein called AvrPiz-t into its host, where it causes widespread changes in immune function. This effector is noteworthy for attacking two components of plant immunity, the reaction to conserved molecular patterns of the pathogen (PAMP-triggered immunity or PTI) and strain-specific immune responses to pathogens (effector-triggered immunity or ETI). Preliminary results indicate that AvrPiz-t represents a novel fungal effector that interacts with the host?s ubiquitination system for both its virulence and immunity inducing activities. In particular, it interacts with three rice enzymes called ubiquitin E3 ligases to suppress their ligase activity and thereby reduce the effectiveness of the host's immune response. The immunosuppressive activity of the pathogen is countered by these same E3 ligases, which ubiquitinate AvrPiz-t to mark it for degradation. This project seeks to understand at the molecular level how AvrPiz-t interacts with host proteins to suppress the host's innate immunity. The specific goals are: (1) Determine the interference, degradation, ubiquitination and PTI suppression mechanisms of AvrPiz-t; (2) Identify the function of an E3 ligase in the regulation of PTI and ETI; and (3) Use genetic and biochemical approaches to gain insight into the relationship between this E3 ligase and the resistance protein that mediates the immune response induced by AvrPiz-t. The project will potentially provide new insights into fungal disease control in rice and other cereal crops. As the staple food for nearly 50% of the world's population, development of new rice blast control strategies from this project will affect food security and social stability in many developing countries. Moreover, this project will provide extensive training opportunities for a postdoctoral fellow and a PhD student who might continue to work on this important disease in the future.

National Science Foundation (NSF)
Division of Integrative Organismal Systems (IOS)
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Michael L. Mishkind
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Ohio State University
United States
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