Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2012
Publication Date: 6/18/2012
Citation: Kuykendall, L.D., Shao, J.Y., Hartung, J.S. 2012. 'Ca. Liberibacter asiaticus' proteins orthologous with pSymA-encoded proteins of Sinorhizobium meliloti: hypothetical roles in plant host interation. PLoS One. 7:e38725. Interpretive Summary: Orange juice producers in Florida have recently been plagued by citrus-greening disease caused by a bacterium related to another well-known bacterial species that promotes the growth of legumes or, more specifically, alfalfa plants. Scientists had compared the chromosomes of the two bacterial species but no one had yet examined a certain DNA element of the alfalfa species for similarity to the citrus greening disease micro-organism. We did that and found specific genes that enable the bacteria to live within plants cells, and this valuable new information is expected lead to effective disease control strategies. Research plant pathologists who are working to solve an intractable problem of citrus greening disease will find this research helpful.
Technical Abstract: A nitrogen-fixing alfalfa-nodulating microsymbiont, Sinorhizobium meliloti, has a genome consisting of a 3.5 Mbp circular chromosome and two megaplasmids totaling 3.0 Mbp, one a 1.3 Mbp pSymA carrying nonessential ‘accessory’ genes including nif, nod and others involved in plant interaction. Predicted protein products of genes of ‘Ca. Liberibacter asiaticus,’ the citrus-greening phytopathogen, were already examined for orthologs encoded by genes on the circular chromosome of S. meliloti. In this study, gene products of pSymA were examined for orthologs and three ‘Ca. Liberibacter asiaticus’ genes were identified that encode proteins orthologous to those encoded by genes on pSymA but not by genes on either the S. meliloti chromosome or pSymB, except for YP_003065337’s relatively weak chromosomal homolog with an 11 orders of magnitude higher Evalue. ‘Ca. Liberibacter’ predicted protein products YP_003064775, YP_003064907 and YP_003065337, with orthologs encoded by genes of pSymA in S. meliloti, are as follows (1) a Na+/K+ antiporter, (2) a Co++, Zn++ and Cd++ cation efflux protein and (3) a redox-regulated K+ efflux pump that regulates cytoplasmic pH, respectively. About 80 other proteins are encoded by orthologs shared albeit not uniquely by pSymA and the ‘Ca. Liberibacter’ genome are presented and discussed.