Identification of Xanthomonas citri ssp. citri host specificity genes in a heterologous expression host

Mol Plant Pathol. 2009 Mar;10(2):249-62. doi: 10.1111/j.1364-3703.2008.00528.x.


We provide the first conclusive evidence that Xanthomonas axonopodis pv. citri Asiatic strain (Xac-A) and, in particular, Xac-A(w), a unique citrus canker A strain isolated from Key lime in Wellington, Florida, induces a hypersensitive reaction (HR) in grapefruit leaves. Using the heterologous tomato pathogen X. perforans, as a recipient of the Xac-A(w) genomic library, we identified a 1599-bp open reading frame responsible for HR in grapefruit, but not Key lime, and designated it avrGf1. Xac-A(w)DeltaavrGf1 produced typical, although visibly reduced, citrus canker symptoms (i.e. raised pustules) in grapefruit and typical canker symptoms in Key lime. We also determined that the X. perforans transconjugant carrying an Xac-A(w) hrpG elicited HR in grapefruit and Key lime leaves, and that xopA in X. perforans was partly responsible for HR. Xac-A transconjugants carrying the X. perforans xopA were reduced in ability to grow in grapefruit leaves relative to wild-type Xac-A. The X. perforans xopA appears to be a host-limiting factor. An avrBs3 homologue, which contained 18.5 repeats and induced HR in tomato, was designated avrTaw. This gene, when expressed in a pustule-minus Xac-A(w), did not complement pustule formation; however, pthA(w), a functional pthA homologue, complemented the mutant strain to produce typical pustules in Key lime, but markedly reduced pustules in grapefruit. Both avrBs3 homologues, when expressed in a typical Xac-A strain, resulted in typical citrus canker pustules in grapefruit, indicating that neither homologue suppressed pustule size in grapefruit. Xac-A(w) contains other unidentified factors that suppress development in grapefruit.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Proteins / metabolism
  • Citrus aurantiifolia / microbiology
  • Citrus paradisi / immunology
  • Citrus paradisi / microbiology
  • Gene Library
  • Genes, Bacterial*
  • Host-Pathogen Interactions / genetics*
  • Lycopersicon esculentum / microbiology
  • Molecular Sequence Data
  • Nucleic Acid Hybridization
  • Plant Diseases / immunology
  • Plant Diseases / microbiology
  • Plant Leaves / immunology
  • Plant Leaves / microbiology
  • Selection, Genetic
  • Sequence Analysis, DNA
  • Sequence Homology, Amino Acid
  • Species Specificity
  • Virulence
  • Xanthomonas / genetics*
  • Xanthomonas / pathogenicity


  • Bacterial Proteins

Associated data

  • GENBANK/DQ275469