Fungal_Senescence_Review

Fungal_Senescence_Review - Annu. Rev. Phytopathol. 2000....

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Unformatted text preview: Annu. Rev. Phytopathol. 2000. 38:397422 Copyright c 2000 by Annual Reviews. All rights reserved R OLE OF M ITOCHONDRIAL DNA IN THE S ENESCENCE AND H YPOVIRULENCE OF F UNGI AND P OTENTIAL FOR P LANT D ISEASE C ONTROL Helmut Bertrand Department of Microbiology, Michigan State University, East Lansing, Michigan 48824; e-mail: mhelmut@pilot.msu.edu Key Words fungi, pathogen, hypovirulence, senescence, mitochondria Abstract The unique coenocytic anatomy of the mycelia of the filamentous fungi and the formation of anastomoses between hyphae from different mycelia enable the intracellular accumulation and infectious transmission of plasmids and mutant mito- chondrial DNAs (mtDNAs) that cause senescence. For reasons that are not fully appar- ent, mitochondria that are rendered dysfunctional by so-called suppressive mtDNA mutations proliferate rapidly in growing cells and gradually displace organelles that contain wild-type mtDNA molecules and are functional. The consequence of this process is senescence and death if the suppressive mtDNA contains a lethal mutation. Suppressive mtDNA mutations and mitochondrial plasmids can elicit cytoplasmically transmissible mitochondrial hypovirulence syndromes in at least some of the phy- topathogenic fungi. In the chestnut-blight fungus Cryphonectria parasitica , the pattern of asexual transmission of mutant mtDNAs and mitochondrial plasmids resembles the pattern of infectious transmission displayed by the attenuating virus that is most commonly used for the biological control of this fungus. At least some of the attenuat- ing mitochondrial hypovirulence factors are inherited maternally in crosses, whereas the viruses are not transmitted sexually. The natural control of blight in an isolated stand of chestnut trees has resulted from the invasion of the local population of C. par- asitica by a senescence-inducing mutant mtDNA. Moreover, a mitochondrial plasmid, pCRY1, attenuates at least some virulent strains of C. parasitica , suggesting that such factors could be applied to control plant diseases caused by fungi. CONTENTS INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 398 FUNGAL SENESCENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399 THE ROLE OF MITOCHONDRIA IN FUNGAL SENESCENCE . . . . . . . . . . . . . 404 The senDNAs of Podospora . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404 Senescence DNAs of Aspergillus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 406 Senescence DNAs in Laboratory Strains of Neurospora . . . . . . . . . . . . . . . . . . . . 406 Senescence Factors in Natural Populations of Neurospora . . . . . . . . . . . . . . . . . . 408 0066-4286/00/0901-0397$14.00 397 398 BERTRAND Mechanisms of Senescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409 MITOCHONDRIAL HYPOVIRULENCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....
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This note was uploaded on 09/14/2010 for the course MMG 431 taught by Professor Bertrand during the Fall '08 term at Michigan State University.

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Fungal_Senescence_Review - Annu. Rev. Phytopathol. 2000....

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