Evolution of the chromosomes in crown gall-causing Agrobacteria
E. DAVIS (1), A. Weisberg (1), J. Tabima (1), M. Putnam (1), M. Miller (1), M. Kohen (1), J. Loper (2), N. Grünwald (2), W. Ream (3), J. Chang (1) (1) Oregon State University, U.S.A.; (2) USDA-ARS Horticultural Crops Research Laboratory, U.S.A.; (3) Oregon State University, U.S.A.

We determined the genome sequences of 120+ gall-associated isolates of Agrobacterium and Rhizobium spp. to construct a phylogenomic framework for a population study of gall-causing agrobacteria. The isolates were selected to maximize genetic diversity of those present in the collection of Larry Moore and that of the Oregon State University’s Plant Clinic, and further augmented with several historical samples. The isolates spanned nine decades of collection and were isolated from over 50 diseased nut trees, fruit trees, and herbaceous plants grown in various regions across the globe. Analysis of the multi-partite chromosome sequences showed that members of both the A. tumefaciens clade (biovar 1) and the R. rhizogenes clade (biovar 2) form monophyletic units, with biovar 1 having more genetic heterogeneity and defined substructure. Several other clades, including isolates identified as A. vitis (biovar 3), a potentially novel gall-causing species primarily isolated from blackberry, and others (A. rubi, A. skierniewicense) are also represented in this dataset. We will present comparisons across these phylogenetically distinct, yet gall-causing, organisms. Additionally, we will present genetic determinants that are candidates for having resulted in differences in speciation. We will also examine potential barriers and enablers of recombination, and evidence of unique chromosomal factors that led to differences in reproductive success and ecological specialization.

Abstract Number: P11-350
Session Type: Poster