Doctor of Philosophy / Department of Plant Pathology / Barbara S. Valent / 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.
| Identifer | oai:union.ndltd.org:KSU/oai:krex.k-state.edu:2097/456 |
| Date | January 1900 |
| Creators | Valdovinos Ponce, Guadalupe |
| Publisher | Kansas State University |
| Source Sets | K-State Research Exchange |
| Language | en_US |
| Detected Language | English |
| Type | Dissertation |
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