Molecular Characterization of Avirulence Gene D from Pseudomonas syringae pv. tomato. D. Y. Kobayashi. Department of Plant Pathology, University of California, Riverside 92521 U.S.A. S. J. Tamaki, and N. T. Keen. Department of Plant Pathology, University of California, Riverside 92521 U.S.A. MPMI 3:94-102. Accepted 3 November 1989. Copyright 1990 The American Phytopathological Society.

A virulence gene D, cloned from Pseudomonas syringae pv. tomato, caused P. s. pv. glycinea to elicit a hypersensitive defense response on certain cultivars of soybean. Nucleotide sequence data for a 5.6-kb HindIII fragment containing avrDdisclosed five long open-reading frames (ORFs) occurring in tandem. The phenotype conferred by avrD was expressed in P. s. pv. glycinea solely by the first of these ORFs (933 bases) that encoded a protein of 34,115 daltons. Neither a signal peptide sequence nor significant regions of hydrophobicity were present that would indicate secretion of the protein or its membrane association. Hybridization analyses revealed that some but not all P. syringae pathovars contained DNA homologous to avrD. This included weak hybridization to all tested races of P. s. pv. glycinea, although none of them express the phenotype conferred by avrD. The avrD gene occurred on an indigenous 75-kb plasmid in several P. s. pv. tomato isolates.