conservation of gene order and content in the circular chromosomes of ‘candidatus liberibacter asiaticus’ and other rhizobiales守恒的环状染色体基因的顺序和内容的candidatus liberibacter asiaticusu201d和其他rhizobiales.pdf

Conservation of Gene Order and Content in the Circular Chromosomes of ‘Candidatus Liberibacter asiaticus’ and Other Rhizobiales L. David Kuykendall, Jonathan Y. Shao, John S. Hartung* Molecular Plant Pathology Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, Maryland, United States of America Abstract ‘Ca. Liberibacter asiaticus,’ an insect-vectored, obligate intracellular bacterium associated with citrus-greening disease, also called ‘‘HLB,’’ is a member of the Rhizobiales along with nitrogen-fixing microsymbionts Sinorhizobium meliloti and Bradyrhizobium japonicum, plant pathogen Agrobacterium tumefaciens and facultative intracellular mammalian pathogen Bartonella henselae. Comparative analyses of their circular chromosomes identified 514 orthologous genes shared among all five species. Shared among all five species are 50 identical blocks of microsyntenous orthologous genes (MOGs), containing a total of 283 genes. While retaining highly conserved genomic blocks of microsynteny, divergent evolution, horizontal gene transfer and niche specialization have disrupted macrosynteny among the five circular chromosomes compared. Highly conserved microsyntenous gene clusters help define the Rhizobiales, an order previously defined by 16S RNA gene similarity and herein represented by the three families: Bartonellaceae, Bradyrhizobiaceae and Rhizobiaceae. Genes without orthologs in the other four species help define individual species. The circular chromosomes of each of the five Rhizobiales species examined had genes lacking orthologs in the other four species. For example, 63 proteins are encoded by genes of ‘Ca. Liberibacter asiaticus’ not shared with other members of the Rhizobiales. Of these 63 proteins, 17 have predicted functions related to DNA repl