Molecular and Cellular Biology of Biotrophic Interactions in Rice Blast Disease

Kansas State University, Manhattan KS

Investigators

Abstract

Title: Molecular and Cellular Biology of Biotrophic Interactions in Rice Blast Disease Successful pathogenesis by plant-infecting fungi often requires an initial period of plant-fungal coexistence, and yet little is known about how a fungus suppresses plant defense mechanisms and establishes itself inside the plant. Rice blast disease occurs when the fungus, Magnaporthe grisea, punctures through the outer plant surface and produces specialized bulbous invasive hyphae inside living rice cells. This project will focus on microscopy coupled with fungal and plant gene expression analyses of the first and second invaded rice cells. Live-cell fluorescence confocal microscopy will be used to define the nature of the plant cytoplasm-fungus interface as invasive hyphae fill the first epidermal cell, approximately 24 to 35 hours after inoculation. Laser Microdissection (LM) and whole genome microarrays, of both fungus and rice, will provide a deep analysis of biotrophic fungal gene expression and of rice cell responses. Similar coupled microscopy and LM-microarray analysis will be performed after 35 hrs when the fungus has completely filled the first epidermal cell and is sending invasive hyphae into all neighboring cells. Cellular and molecular interactions in a successful biotrophic infection will be compared to the near-isogenic interaction in which fungal growth is blocked by Pi-ta resistance gene-mediated hypersensitive resistance. This research will identify genes showing differential expression in biotrophic hyphae or in plant cells responding to these hyphae. Expression patterns will be confirmed for differentially-expressed fungal genes. Functional analysis of biotroph-specific fungal genes will include live-cell microscopy of infection by gene-disruption mutants to link molecular and cellular phenotypes. Broader Impacts: Understanding the cellular and molecular mechanisms that determine if crop plants succumb to or resist disease will lead the way to developing durable disease resistance. Food security in the coming century depends on decreasing the potential for rice blast disease to cause catastrophic losses to rice production. In addition, studying biotrophic blast infection will aid research on other hemibiotrophic and biotrophic fungi that cause many plant diseases threatening agriculture. Success in using LM to define temporal and spatial details early in development of rice blast disease has the potential to revolutionize studies of fungus-plant interactions. This technology has exciting potential to enable a deep molecular analysis of plant infection structures formed by obligate pathogens such as the rust fungi, which fail to grow outside of plant tissue. This project will provide a stimulating learning and research experience for graduate and undergraduate students at K-State. The strikingly visual picture of an important fungus-plant struggle that emerges from this research will be presented in lectures at high schools and community colleges. A special challenge lies in attracting kids from an increasingly urbanized population to careers in agricultural research on organisms that are critical for food security in the US and worldwide. This research will be published and made available on the Valent Lab Web Site (http://www.oznet.ksu.edu/plantpath/valentlab/) or on M. grisea community web sites such as the NSF-funded "MGOS" database (http://www.mgosdb.org/