Progress 01/01/02 to 12/31/02
Outputs
Habitat diversity in the fungus Nectria haematococca is partially due to unique habitat-defining genes that are present on "Conditionally Dispensable" (CD) chromosomes. One of these CD chromosomes contains a cluster of genes (PEP cluster for pea pathogenicity), which allows isolates to cause a root rot disease on pea plants. Our research has shown that the CD chromosome carrying the PEP cluster also carries a gene(s) for utilization of homoserine, an amino acid present in pea root exudates. A screen of isolates from a variety of hosts and geographical locations demonstrated that isolates pathogenic on pea grew on homoserine, while nonpathogenic isolates did not. Isolates that had lost the CD chromosome also lost the ability to grow on homoserine. Conventional genetic analyses suggested that homoserine utilization is encoded by more than one gene (HUT genes), but that at least one HUT gene is on a CD chromosome. We propose that HUT genes provide isolates carrying them a
competitive advantage in the pea rhizosphere, prior to the establishment of a pathogenic association with the roots. A second study is using real time PCR to measure whether isolates with a CD chromosome are better colonizers of the rhizosphere. Preliminary results support this hypothesis.
Impacts
Once genes enhancing competitiveness in the rhizosphere are identified, whether from pathogens or commensal organisms, these genes and the counterpart genes in plants that are involved in the rhizosphere effects will be of great utility for manipulating the rhizospheres of plants in order to control processes such as the efficiency of nitrogen fixation, biological control and bioremediation. Such manipulations should allow us to increase the health of plants, the soil they occupy and the water that runs that soil.
Publications
- Rodriguez and VanEtten, H.D. 2003 Genes for pea pathogenicity and a Gene for for utilizing a specific pea root exudate are located on the same supernumerary chromosome in Nectria haematococca. XXII Fungal Genetics Conference. Pg 130.
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Progress 01/01/01 to 12/31/01
Outputs
Habitat diversity in the fungus Nectria haematococca is partially due to unique habitat-defining genes that are present on "Conditionally Dispensable" (CD) chromosomes. One of these CD chromosomes contains a cluster of genes (PEP cluster for pea pathogenicity), which allows isolates to cause a root rot disease on pea plants. Our research has shown that the CD chromosome carrying the PEP cluster also carries a gene(s) for utilization of homoserine, an amino acid present in pea root exudates. A screen of isolates from a variety of hosts and geographical locations demonstrated that isolates pathogenic on pea grew on homoserine, while nonpathogenic isolates did not. Isolates that had lost the CD chromosome also lost the ability to grow on homoserine. Conventional genetic analyses suggested that homoserine utilization is encoded by more than one gene (HUT genes), but that at least one HUT gene is on a CD chromosome. We propose that HUT genes provide isolates carrying them
a competitive advantage in the pea rhizosphere, prior to the establishment of a pathogenic association with the roots.
Impacts
(N/A)
Publications
- Rodriguez, M.C., Temporini, E.D., and VanEtten, H.D. 2001. Pea Pathogenicity Genes and a Gene(s) for for utilizing a Pea Root Exudate Are Located on the Same Supernumerary Chromosome in Nectria haematococca. In: Rhizosphere Control Points: Molecules to Food Webs. University of California, Davis Rhizosphere Biology Program, 2001 p31.
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Progress 01/01/00 to 12/31/00
Outputs
Although microorganisms living in the immediate vicinity of the roots can have large effects on the health of plants and the soil they inhabit, little is known about the specific properties that allow specific microorganisms to grow in this location. The goal of this research is to characterize the genes in a soil-borne fungus that define its capacity to survive and compete in the immediate vicinity of the roots. The experimental system involves highly evolved plant-microbe relationships in which the presence of conditionally dispensable (CD) chromosomes in the fungus, Nectria haematococca, is linked to its capacity to live on or within root systems of a particular plant species. These interactions range from prolific growth of the fungus in the soil in the immediate vicinity of specific plant roots without damage to the roots to an invasive pathogenesis of the root per se. The nature of these interactions is at least in part dictated by the interplay of products of
the habitat-defining CD chromosome with chemicals from plant roots. For example, one CD chromosome gene product (Hut) can specifically metabolize a naturally occurring amino acid present at high levels in pea root exudates. The goal of this proposal is to systematically evaluate the contribution of HUT and potentially other CD-chromosome encoded genes to the rhizosphere competitiveness of N. haematococca. Identifying the genes for rhizosphere colonization along with the plant's counterparts could provide the tools to manipulate rhizosphere populations to benefit the health of plants and the soil they inhabit.
Impacts
(N/A)
Publications
- Funnell, D. L., P.S. Matthews and H. D. VanEtten. 2001. Breeding for highly fertile isolates of Nectria haematococca MPVI that are highly virulent on pea and in planta selection for virulent recombinants. Phytopathology 91: 92-101.
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