Genomics of xanthomonas citri and related species

Abstract

Citrus canker is a devastating disease that affects most commercial citrus varieties. Asiatic type canker is the most widespread and destructive form of citrus canker that is caused by Xanthomonas citri subsp. citri (XccA). Multiple variants of XccA including XccAw and XccA∗have been reported. Citrus canker is also known to be caused by X. fuscans subsp. aurantifolii (Xau) B and C strains. XccAw, XccA∗, XauB, and XauC, unlike XccA, are limited in host range. The complete genome sequence of XccA strain 306 was sequenced in 2002 using Sanger sequencing. With advances in sequencing technologies, other strains associated with citrus canker were also sequenced recently. Currently, draft sequences of XauB and XauC are available. The complete genome of XccAw strain 12879 has been sequenced, whereas XccA∗strain 270 is currently being sequenced. Furthermore, the complete genome of another closely related citrus pathogen, X. axonopodis pv. citrumelo strain F1 causing citrus bacterial spot, has also been sequenced. Multilocus sequence phylogenetic analysis of XccA and other xanthomonads indicates that citrus canker pathogens XccA, XccAw, XauB, and XauC form a closely related group. In this review, the following topics were included: an introduction about citrus canker including the origin of citrus canker, its current distribution, economic losses, infection cycle; current understanding of the virulence mechanisms of XccA; genome information of XccA and related species; genome-enabled understanding of X. citri virulence and host specificity; and transcriptomics of X. citri. The advent of next generation sequencing will dramatically promote the genomic study of X. citri and investigation of the virulence mechanisms of X. citri to design innovative strategies to control citrus canker and other bacterial diseases.