Regulation of expression of avirulence gene avrRxv and identification of afamily of host interaction factors by sequence analysis of avrBsT

Resistance in tomato line Hawaii 7998 as well as in several nonhost plants to Xanthomonas campestris pv. vesicatoria tomato strain (XcvT) is mediated in part by the avirulence gene avrRxv, Analysis of growth of wild-type and avrRxv deletion strains indicates that avrRxv plays a crucial role in the a bility of XcvT 92-14 to induce resistance on Hawaii 7998. We used avrRxv re porter gene fusions and Northern (RNA) blot analysis to test several growth environments for inductive potential. We found that avrRxv is constitutive ly expressed at high levels and that growth in planta, in tobacco condition ed medium, and in hrp-inductive medium XVM2 did not affect the high levels of expression. In addition, hrp structural and regulatory mutant background s had no effect, We mutated the bipartite plant inducible promoter (PIP)-bo x sequence and found that avrRxv activity appears to be independent of an i ntact Pm-box element, We present the sequence of the avrRxv homologue calle d avrBsT and align the six AvrRxv host interaction factor family members in cluding mammalian pathogen virulence factors YopJ and YopP from Yersinia sp p. and AvrA from Salmonella typhimurium, and open reading frame Y4LO with u nknown function from the symbiont Rhizobium sp.