AVIRULENCE GENE AVRRXV FROM XANTHOMONAS-CAMPESTRIS PV VESICATORIA SPECIFIES RESISTANCE ON TOMATO LINE HAWAII-7998

The molecular and genetic control of the interaction between tomato ra ces of Xanthomonas campestris pv. vesicatoria (XcvT) and tomato was st udied. Based on inoculation phenotype and analysis of in planta bacter ial growth, tomato line Hawaii 7998 is resistant to XcvT race 1 75-3 b ut not to XcvT race 2 89-1. Two cosmid clones from a genomic library o f XcvT race 1 75-3 converted the normally virulent race 2 89-1 to avir ulence on Hawaii 7998. The two clones contained the previously isolate d, nonhost avirulence gene avr-Rxv, and their activity was localized t o a 2.1-kbp subclone of avrRxv. avrRxv inhibits growth of race 2 89-1 in the resistant line Hawaii 7998 and an insertional mutation in avrRx v prevents this inhibition. In addition, a dramatic increase in electr olyte leakage of leaves of Hawaii 7998 occurred after 12-hr postinfilt ration with race 2 89-1 carrying avrRxv. The nucleotide sequence of av rRxv revealed one major open reading frame (ORF) that accords well wit h activity analysis of nested deletions. ORF 2-2 encodes a putative pr otein of 374 amino acids with a molecular weight of 42.1 kDa and a pI of 10.7. Inheritance of the avrRxv-specific resistance in Hawaii 7998 was studied in a total of 587 F-2 individuals from crosses between Haw aii 7998 and susceptible lines. The inheritance of avrRxv-specific res istance in Hawaii 7998 appears to be governed by more than one locus.