Submitted to: American Phytopathology Society
Publication Type: Abstract Only
Publication Acceptance Date: 4/20/2007
Publication Date: 7/28/2007
Citation: Doddapaneni, H., Lin, H., Bai, X., Zhao, X., Civerolo, E.L. 2007. Comparative Genomics and Phylogenetic Analyses of Newly Cloned Genomic Regions From the Citrus Huanglongbing (HLB)-associated Bacterium Candidatus Liberibacter. American Phytopathology Society. 97(7):29
Technical Abstract: Huanglongbing (HLB), or citrus greening disease, caused by Candidatus Liberibacter species, is a serious threat to citrus production worldwide. The pathogen is a gram negative, unculturable, phloem-limited bacterium, with little known genomic information. Here, we report cloning and characterization of 12 Kbp of genomic DNA from Candidatus Liberibacter asiaticus (Las). This includes three genes from a cluster (trmU, tufB and rpoB), two from the OMP gene region (yaeL, lpxD and fabZ) and 1,600 bp of the 16S-23S rRNA region. In addition, a pseudogene for D-3-phosphoglycerate dehydrogenase was detected, suggesting possible ongoing gene decay that may reflect bacterium’s physiological status as an unculturable microbe. Analysis of a 1,508 bp fragment of the rpoB gene of Las strains from China, Brazil, Florida and Japan and Ca. L. africanus (Laf) strains from South Africa identified SNPs. Phylogenetic analyses of the deduced protein sequences and 16S rRNA characterizes Candidatus Liberibacter as a new clade in the sub-division of the '-proteobacteria. Comparative analyses of the genome organization of Candidatus Liberibacter with members of the order Rhizobiales suggest similar gene sequence, structure and order, albeit with minor variations. Genomic regions cloned in this study will help in designing better diagnostic protocols for strain differentiation and phylogenetic evaluation, and developing improved disease management strategies.