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Applied and Environmental Microbiology, June 2008, p. 3849-3856, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.00351-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Supernumerary Chromosome of Nectria haematococca That Carries Pea-Pathogenicity-Related Genes Also Carries a Trait for Pea Rhizosphere Competitiveness

M. Rodriguez-Carres ,^, G. White, D. Tsuchiya, M. Taga,^¶ and H. D. VanEtten^*

Division of Plant Pathology and Microbiology, Department of Plant Science, University of Arizona, Tucson, Arizona 85721

Received 11 February 2008/ Accepted 7 April 2008

Fungi are found in a wide range of environments, and the ecological and host diversity of the fungus Nectria haematococca has been shown to be due in part to unique genes on different supernumerary chromosomes. These chromosomes have been called "conditionally dispensable" (CD) since they are not needed for axenic growth but are important for expanding the host range of individual isolates. From a biological perspective, the CD chromosomes can be compared to bacterial plasmids that carry unique genes that can define the habits of these microorganisms. The current study establishes that the N. haematococca PDA1-CD chromosome, which contains the genes for pea pathogenicity (PEP cluster) on pea roots, also carries a gene(s) for the utilization of homoserine, a compound found in large amounts in pea root exudates. Competition studies demonstrate that an isolate that lacks the PEP cluster but carries a portion of the CD chromosome which includes the homoserine utilization (HUT) gene(s) is more competitive in the pea rhizosphere than an isolate without the CD chromosome.

Published ahead of print on 11 April 2008.

M.R.-C. and G.W. contributed equally to this research.

Present address: Department of Molecular Genetics and Microbiology, Duke University Medical Center, Durham, NC 27710.

Present address: Department of Biology, Indiana University, Bloomington, IN 47405.

^¶ Present address: Department of Biology, Faculty of Science, Okayama University, Okayama 700-8530, Japan.