XANTHOMONAS AVIRULENCE PATHOGENICITY GENE FAMILY ENCODES FUNCTIONAL-PLANT NUCLEAR TARGETING SIGNALS/

Pathogenic symptoms and host range of some Xanthomonas strains are det ermined in part by a family of avirulence/pathogenicity genes widely d istributed in the genus. We identified heptad repeats similar to leuci ne zippers and three putative nuclear localization signals (NLSs) in t he C-terminal regions of the predicted proteins of all sequenced membe rs. The DNA coding sequences for the C-terminal regions of two members of the gene family with pathogenicity function (avrb6 and pthA) were independently fused to a beta-glucuronidase (GUS) reporter gene, When introduced into onion cells, both of these translational fusions were transiently expressed, and GUS activity was specifically localized in the nuclei of transformed cells, Protein extracts containing PthA elic ited no symptoms when inoculated onto plants; hrp genes were required for Xanthomonas carrying pthA to elicit hyperplastic canker symptoms o n citrus.