The ascomycete fungus Magnaporthe oryzae, causative agent of rice blast disease, poses a threat to global food security, destroying enough rice to feed 60 million people each year. Characterization of the host-pathogen interaction between rice and M. oryzae is critical, as better understanding of the system may lead to better disease control strategies. The sequenced genome and repertoire of molecular tools available have made M. oryzae an ideal model system for understanding general plant-pathogen interactions as well.
The objective of this dissertation was to characterize the M. oryzae homologs of Histoplasma capsulatum RYP ( Required for Yeast Phase ) genes that are required for transition to the parasitic phase. H. capsulatum is a human pathogen that undergoes a dimorphic switch from filamentous to yeast cell growth at 37°C, the host body temperature. FourH. capsulatum RYP genes were identified in a forward genetic screen to identify genes required for entry into the yeast phase. RYP1 is a member of the Gti1_Pac2 family, which contains previously characterized regulators of dimorphic switching. RYP2 and RYP3 are homologs of vosA and velB, members of the Velvet family, best characterized in Aspergillus nidulans, where they coordinate morphological differentiation with secondary metabolism. RYP4 is a zinc binuclear cluster protein, a main class in the zinc finger transcription factor family. Deletion of the M. oryzae RYP1 homolog, RIG1 ( Required for Infectious Growth ), resulted in a non-pathogenic mutant on susceptible rice cultivars, even upon removal of the host penetration barrier. Δrig1 was blocked in the transition to infectious hyphal growth, similar to H. capsulatum ryp1, which could not transition to the yeast phase. Deletion mutants of M. oryzae RYP2, RYP3, and RYP4 homologs were similar to the wild type in somatic growth and pathogenicity indicating that although RIG1 is a pathogenicity factor conserved in plant and animal pathogens, such conservation does not apply to all of the RYP pathogenicity genes identified in H. capsulatum.
Δrig1 is the first M. oryzae mutant known to be blocked in production of primary infection hyphae. Overall, the study suggests limited parallels exist in phase transition of fungal pathogens of plants and animals.
|Advisor:||Orbach, Marc J.|
|Commitee:||Cotty, Peter J., Palanivelu, Ravishankar, Tax, Frans E., VanEtten, Hans D.|
|School:||The University of Arizona|
|School Location:||United States -- Arizona|
|Source:||DAI-B 74/09(E), Dissertation Abstracts International|
|Subjects:||Molecular biology, Microbiology, Plant Pathology|
|Keywords:||Gti1_pac2 family, Histoplasma capsulatum, Magnaporthe oryzae, RYP gene, Rig1|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be