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Molecular and cellular analyses of pathogenicity and host specificity in rice blast disease

by Valdovinos Ponce, Guadalupe

Abstract (Summary)
Rice (Oryza sativa L.) production worldwide is constrained by rice blast disease caused

by the ascomycetous fungus Magnaporthe oryzae. Rice blast has become a model system for the

study of fungal plant diseases based on its global relevance to agriculture and on our ability to

apply molecular genetic and genomic analyses to both the pathogen and the plant. We have

applied molecular and cellular analyses to understand critical processes in the M. oryzae disease

cycle. The dark melanin pigment produced by the fungus is critical for the function of its

specialized appressorial cell, which punches the leaf surface by generating the highest pressure

known in any biological system, estimated at 80 times the atmospheric pressure. Without

melanin, the fungus can neither generate this pressure nor puncture the plant surface and disease

does not occur. M. oryzae genome sequencing identified a cluster of melanin biosynthesis genes

that included an attractive candidate for the transcription factor that regulates melanin

biosynthesis in appressoria. We report the structural and functional characterization of this

putative transcription factor, although its role remains elusive. Host cellular responses after

appressorial penetration are equally important in determining if disease will occur. We have

characterized the cellular response of one rice variety to a compatible fungal strain (causes

disease), an incompatible strain (fails to cause disease due to specific triggering of rice defenses)

and a non-host strain (causes disease in barley but not in rice). Distinctive fungal and rice

cellular responses correlated with the outcome of each particular pathogen-strain rice interaction.

We report contrasting responses in two rice leaf sheath assays that are amenable to live cell

microscopy, as well as a novel cellular response of crystalline aggregations deposited inside the

host cell under appressoria on the leaf surface. Our studies have important implications for future

analyses of pathogenicity and host specificity in rice blast disease.

Bibliographical Information:

Advisor:

School:Kansas State University

School Location:USA - Kansas

Source Type:Master's Thesis

Keywords:melanin appressorium transcription factors non host resistance magnaporthe oryzae biology molecular 0307

ISBN:

Date of Publication:01/01/2007

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