<p> The ascomycete fungus <i>Magnaporthe oryzae,</i> 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 <i>M. oryzae</i> 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 <i> M. oryzae</i> an ideal model system for understanding general plant-pathogen interactions as well. </p><p> The objective of this dissertation was to characterize the <i>M. oryzae</i> homologs of <i>Histoplasma capsulatum RYP</i> (<i><u> R</u>equired for <u>Y</u>east <u>P</u>hase </i>) genes that are required for transition to the parasitic phase. <i> H. capsulatum</i> is a human pathogen that undergoes a dimorphic switch from filamentous to yeast cell growth at 37°C, the host body temperature. Four<i>H. capsulatum RYP</i> genes were identified in a forward genetic screen to identify genes required for entry into the yeast phase. <i> RYP1</i> is a member of the Gti1_Pac2 family, which contains previously characterized regulators of dimorphic switching. <i>RYP2</i> and <i> RYP3</i> are homologs of <i>vosA</i> and <i>velB,</i> members of the Velvet family, best characterized in <i>Aspergillus nidulans, </i> where they coordinate morphological differentiation with secondary metabolism. <i>RYP4</i> is a zinc binuclear cluster protein, a main class in the zinc finger transcription factor family. Deletion of the <i> M. oryzae RYP1</i> homolog, <i>RIG1</i> (<i><u> R</u>equired for <u>I</u>nfectious <u>G</u>rowth </i>), resulted in a non-pathogenic mutant on susceptible rice cultivars, even upon removal of the host penetration barrier. <i>Δrig1</i> was blocked in the transition to infectious hyphal growth, similar to <i> H. capsulatum ryp1,</i> which could not transition to the yeast phase. Deletion mutants of <i>M. oryzae RYP2, RYP3,</i> and <i>RYP4 </i> homologs were similar to the wild type in somatic growth and pathogenicity indicating that although <i>RIG1</i> is a pathogenicity factor conserved in plant and animal pathogens, such conservation does not apply to all of the <i>RYP</i> pathogenicity genes identified in <i>H. capsulatum. </i> </p><p> <i>Δrig1</i> is the first <i>M. oryzae</i> 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.</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3560871 |
| Date | 07 June 2013 |
| Creators | Wickramage, Amritha Suhasini |
| Publisher | The University of Arizona |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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