Is less actually more? Does the absence of group-specific DNA fragments in Acidovorax citrulli contribute to broaden its host range?
N. ECKSHTAIN-LEVI (1), D. Shkedy (2), M. Gershovits (2), G. Mateus Da Silva (3), R. Walcott (3), T. Pupko (2), S. Burdman (4) (1) Department of Plant Pathology, Physiology and Weed Science, Virginia Polytechnic Institute and State University, U.S.A.; (2) Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel; (3) Department of Plant Pathology, College of Agricultural and Environmental Sciences, University of Georgia, U.S.A.; (4) Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, The Hebrew University of Jerusalem, Israel

Bacterial fruit blotch (BFB) of cucurbits is caused by the Gram-negative bacterium Acidovorax citrulli (Ac). Serious economic losses due to BFB have been reported in watermelon and melon in many parts of the world. Ac requires a functional type III secretion system (T3SS) for pathogenicity. The T3SS injects effector proteins directly into the cytosol of plant cells, which collectively allow the pathogen to manipulate host cellular activities to its own benefit. Comparative analyses of effector sequences from various Ac strains combined with additional experimental data support the existence of at least three groups within Ac. We used comparative genome analysis to investigate differences between two model strains, M6 and AAC00-1, belonging to group I and II, respectively. The approximate size of the draft genome sequence of M6 is 4.85 Mb, ~500 Kb shorter than that of strain AAC00-1. Comparative analysis revealed that this size difference is mainly explained by eight fragments, ranging from ~30 to 120 kb, distributed throughout the AAC00-1 genome, which are absent in the M6 genome. Interestingly, strain M6 has been shown to be a highly aggressive strain in all cucurbits tested so far, including watermelon, whereas group II strains are strongly associated with watermelon and have moderate virulence on other cucurbits. Further analyses by PCR assays and coverage analyses with other Ac strains support the notion that most, if not all, of these fragments are group II specific. GC content of these fragments combined with other analyses suggest that they have been acquired by horizontal gene transfer.

Abstract Number: P11-352
Session Type: Poster