This family consists of Rhizobium NolX and Xanthomonas HrpF proteins. The interaction between the plant pathogen Xanthomonas campestris pv. vesicatoria and its host plants is controlled by hrp genes (hypersensitive reaction and pathogenicity), which encode a type III protein secretion system. Among type III-secreted proteins are avirulence proteins, effectors involved in the induction of plant defense reactions. HrpF is dispensable for protein secretion but required for AvrBs3 recognition in planta, is thought to function as a translocator of effector proteins into the host cell. NolX, a soybean cultivar specificity protein, is secreted by a type III secretion system (TTSS) and shows homology to HrpF of the plant pathogen Xanthomonas campestris pv. vesicatoria. It is not known whether NolX functions at the bacterium-plant interface or acts inside the host cell. NolX is expressed in planta only during the early stages of nodule development.