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The filamentous fungus, Magnaporthe oryzae, responsible for blast rice disease, destroys around 10-30% of the rice crop annually. Infection begins when the specialized infection structure, the appressorium, generates enormous internal turgor pressure through the accumulation of glycerol. This turgor acts on a penetration peg emerging at the base of the cell, causing it to breach the leaf surface allowing its infection.
The enzyme trehalose-6- phosphate synthase (Tps1) is a central regulator of the transition from appressorium development to infectious hyphal growth. In the first chapter we show that initiation of rice blast disease requires a regulatory mechanism involving an NADPH sensor protein, Tps1, a set of NADP-dependent transcriptional inhibitors and the nonconsuming interconversion of NADPH and NADP acting as signal transducer.
The Tps1-dependent Nmr inhibitor proteins regulate the activity of GATA-family transcription factors that are involved in several essential aspects of the life style of the fungus. Thus, We elucidated that the GATA transcription factor Asd4 is
essential for pathogenicity and is a positive regulator of appressorium development and sporulation, in contrast to the GATA transcription factor Pas1 that is a negative regulator of appressorium development and sporulation.
In chapter two, we set out to understand the specific role of the GATA transcription factor Asd4. We show that Asd4 controls the activation of the Tor kinase pathway, which is essential for virulence and integrates important processes such as regulation of transcription, translation, ribosome biogenesis, trafficking and regulation of Golgi, secondary metabolism, autophagy and nitrogen metabolism. This mechanism is essential to the initiation of infection-associated autophagy during plant infection and during in planta invasion.
In summary, in this study we characterized two essential regulators, Tps1 and Asd4, in M. oryzae, and we believe that understanding the regulatory mechanisms that allow the fungus to cause disease may provide new means to control the rice blast pathogen and play an important role in ensuring global food security in the future.
Adviser: Richard A. Wilson
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