Xanthomonas Avirulence/Pathogenicity Gene Family Encodes Functional Plant Nuclear Targeting Signals. Yinong Yang . Plant Molecular and Cellular Biology Program and Plant Pathology Department, University of Florida, Gainesville, FL 32611, U.S.A. Dean W. Gabriel. Plant Molecular and Cellular Biology Program and Plant Pathology Department, University of Florida, Gainesville, FL 32611, U.S.A. MPMI 8:627-631. Accepted 26 April 1995. Copyright 1995 The American Phytopathological Society.

Pathogenic symptoms and host range of some Xanthomonas strains are determined in part by a family of avirulence/pathogenicity genes widely distributed in the genus. We identified heptad repeats similar to leucine zippers and three putative nuclear localization signals (NLSs) in the C-terminal regions of the predicted proteins of all sequenced members. 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 (-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 elicited no symptoms when inoculated onto plants; hrp genes were required for Xanthomonas carrying pthA to elicit hyper-plastic canker symptoms on citrus.