Ti plasmids cluster genetically and cluster by Agrobacterium taxa and plant host type
A. WEISBERG (1), E. Davis (1), J. Tabima (1), M. Putnam (1), M. Miller (1), M. Kohen (1), J. Loper (2), N. Grünwald (2), W. Ream (1), J. Chang (1) (1) Oregon State University, U.S.A.; (2) USDA ARS, U.S.A.

Ti plasmid-carrying Agrobacterium cause crown gall disease on diverse plant hosts, resulting in millions of dollars in damage to orchards and nurseries each year. Analysis of the few sequenced Ti plasmids has revealed a mosaic structure suggestive of a high level of recombination that masks their evolutionary history. We sequenced and assembled the genomes of more than 140 gall-inducing Agrobacterium isolates from the “Larry Moore” collection and the Plant Clinic at Oregon State University, selected to maximize diversity in host species, geographic location, and year of isolation. Ti plasmid-associated genes were clustered to determine the overall Ti plasmid gene pool and categorized based on levels of conservation. The most conserved included those associated with T-DNA, virulence, and plasmid conjugation genes. Other genes were identified that could discriminate between plasmid clusters. A third category of rare genes was substantially large. Presence/absence polymorphisms of genes were used to cluster Ti plasmids to infer evolutionary relationships. Maximum likelihood phylogenies were constructed for T-DNA and non-transferred virulence genes to infer the evolutionary history of different elements of the Ti plasmid. Our analyses show that the Ti plasmids can be clustered into distinct types, and revealed a preference of Ti plasmid types to taxa of Agrobacterium and plant host of initial isolation, indicative of barriers that limit exchange between Ti plasmid types.

Abstract Number: P11-382
Session Type: Poster