The Effect of Conditionally Dispensable Chromosomes on Rhizosphere Colonization by the Fungus Nectria haematococca MPVI

Persistent Link:
http://hdl.handle.net/10150/195145
Title:
The Effect of Conditionally Dispensable Chromosomes on Rhizosphere Colonization by the Fungus Nectria haematococca MPVI
Author:
White, Gerard Joseph
Issue Date:
2008
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
The habitat diversity of the fungus Nectria haematococca MPVI has been shown to be due in part to conditionally dispensable (CD) chromosomes that carry habitat-defining genes. From a biological perspective, the CD chromosomes are analogous to plasmids that possess genes that determine the habitats of plant-associated bacteria. This study establishes that the N. haematococca CD chromosome that contains the genes for Pea Pathogenicity (PEP cluster) also carries genes for the utilization of homoserine, an amino acid found in pea root exudates. Competition studies presented here demonstrate that an isolate that lacks the PEP cluster, but carries a portion of the CD chromosome containing the homoserine utilization (HUT) genes, is more competitive in the pea rhizosphere than an isolate without the CD chromosome. Further competition studies show that both the PDA1 and PDA6 CD chromosomes confer a competitive advantage in the rhizosphere of soybean, whereas only the PDA6 CD chromosome confers a competitive advantage in the rhizospheres of tomato and alfalfa, and only the PDA1 CD chromosome confers a competitive advantage in the rhizosphere of pea. These studies suggest the presence of genes on the PDA6 and PDA1 CD chromosomes that enhance the ability of N. haematococca to expand its habitat and support the idea that fungal CD chromosomes are analogous to host-specifying plasmids in plant-associated bacteria. Transformation, insertional mutagenesis, and bioinformatics were used to identify a cluster of five genes on the PDA1 CD chromosome that was responsible for the HUT phenotype in N. haematococca. One of the genes was found only in N. haematococca, another was a fungal transcription factor, and the other three had homologs involved in the synthesis of the amino acids methionine, threonine, and isoleucine, in which homoserine is an intermediate. Competition experiments that compared isolates with or without the HUT cluster showed that the HUT cluster is responsible for increased competitive ability of HUT+ N. haematococca isolates in the rhizosphere of pea. This study establishes that homoserine utilization can be a rhizosphere competency trait for N. haematococca and, to our knowledge, is the first example of a rhizosphere competency trait identified in a fungus.
Type:
text; Electronic Dissertation
Keywords:
competition; fungi; gene cluster; PCR; plant-pathogen; rhizosphere
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Plant Pathology; Graduate College
Degree Grantor:
University of Arizona
Advisor:
VanEtten, Hans D.
Committee Chair:
VanEtten, Hans D.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleThe Effect of Conditionally Dispensable Chromosomes on Rhizosphere Colonization by the Fungus Nectria haematococca MPVIen_US
dc.creatorWhite, Gerard Josephen_US
dc.contributor.authorWhite, Gerard Josephen_US
dc.date.issued2008en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractThe habitat diversity of the fungus Nectria haematococca MPVI has been shown to be due in part to conditionally dispensable (CD) chromosomes that carry habitat-defining genes. From a biological perspective, the CD chromosomes are analogous to plasmids that possess genes that determine the habitats of plant-associated bacteria. This study establishes that the N. haematococca CD chromosome that contains the genes for Pea Pathogenicity (PEP cluster) also carries genes for the utilization of homoserine, an amino acid found in pea root exudates. Competition studies presented here demonstrate that an isolate that lacks the PEP cluster, but carries a portion of the CD chromosome containing the homoserine utilization (HUT) genes, is more competitive in the pea rhizosphere than an isolate without the CD chromosome. Further competition studies show that both the PDA1 and PDA6 CD chromosomes confer a competitive advantage in the rhizosphere of soybean, whereas only the PDA6 CD chromosome confers a competitive advantage in the rhizospheres of tomato and alfalfa, and only the PDA1 CD chromosome confers a competitive advantage in the rhizosphere of pea. These studies suggest the presence of genes on the PDA6 and PDA1 CD chromosomes that enhance the ability of N. haematococca to expand its habitat and support the idea that fungal CD chromosomes are analogous to host-specifying plasmids in plant-associated bacteria. Transformation, insertional mutagenesis, and bioinformatics were used to identify a cluster of five genes on the PDA1 CD chromosome that was responsible for the HUT phenotype in N. haematococca. One of the genes was found only in N. haematococca, another was a fungal transcription factor, and the other three had homologs involved in the synthesis of the amino acids methionine, threonine, and isoleucine, in which homoserine is an intermediate. Competition experiments that compared isolates with or without the HUT cluster showed that the HUT cluster is responsible for increased competitive ability of HUT+ N. haematococca isolates in the rhizosphere of pea. This study establishes that homoserine utilization can be a rhizosphere competency trait for N. haematococca and, to our knowledge, is the first example of a rhizosphere competency trait identified in a fungus.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectcompetitionen_US
dc.subjectfungien_US
dc.subjectgene clusteren_US
dc.subjectPCRen_US
dc.subjectplant-pathogenen_US
dc.subjectrhizosphereen_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplinePlant Pathologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorVanEtten, Hans D.en_US
dc.contributor.chairVanEtten, Hans D.en_US
dc.contributor.committeememberHawes, Martha C.en_US
dc.contributor.committeememberOrbach, Marc J.en_US
dc.contributor.committeememberOlsen, Mary W.en_US
dc.contributor.committeememberRensing, Christopheren_US
dc.identifier.proquest10044en_US
dc.identifier.oclc659749984en_US
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