Gene-for-Gene Interactions Between Pseudomonas syringae pv. phaseolicola and Phaseolus. Carol Jenner. Department of Biochemistry and Biological Sciences, Wye College, Ashford, Kent, TN25 5AH, U.K.. Ed Hitchin(1), John Mansfield(1), Karen Walters(1), Peter Betteridge(2), Dawn Teverson(3), and John Taylor(3). (1)Department of Biochemistry and Biological Sciences, Wye College, Ashford, Kent, TN25 5AH, U.K.; (2)Shell Research Ltd., Sittingbourne, Kent, ME9 8AC, U. K.; and (3)Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, U.K.. MPMI 4:553-562. Accepted 2 May 1991. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1991.

The gene for cultivar-specific avirulence to Phaseolus vulgaris cv. Tendergreen in races 3 and 4 of Pseudomonas syringae pv. phaseolicola was isolated and sequenced. Genomic clones from libraries of race 3 in pLAFR1 and race 4 in pLAFR3, which altered the phenotype of race 5 from virulent to avirulent in Tendergreen, were found to possess a common ~15-kb region of DNA that contained the determinant of avirulence. Subcloning and insertion mutagenesis with Tn1000 located an avirulence gene within a 1.4-kb BglII/HindIII DNA fragment in races 3 and 4. Comparison of the nucleotide sequences of regions of DNA that confer avirulence confirmed that both races have an identical gene for avirulence (designated avrPph3) comprising 801 base pairs (bp) and predicted to encode a cytoplasmic protein of 28,703 Da. A sequence, TGCAACCGAAT, 91% homologous to the motif found in promoter regions of avrB and avrD from P. s. pv. glycinea was located 89-99 bp upstream of the start of the open-reading frame 1. Hybridization experiments showed that avrPph3 was not plasmid-borne and was absent from isolates of P. s. pv. phaseolicola races 1, 2, 5, 6, 7, and 8, P. cichorii, P. s. pvs. coronafaciens, glycinea, maculicola, pisi, syringae, and tabaci. Cosegregation studies of crosses between cultivars resistant (Tendergreen) and susceptible (Canadian Wonder) to races 3 and 4 and transconjugants of race 5 confirmed that a gene-for-gene relationship controls specificity in the interaction between Tendergreen and races 3 and 4 of P. s. pv. phaseolicola.