The XA21 binding protein XB25 is required for maintaining XA21-mediated disease resistance.

Plant genomes encode a large number of proteins that potentially function as immune receptors in the defense against pathogen invasion. As a well-characterized receptor kinase consisting of 23 tandem leucine-rich repeats, a transmembrane domain and a serine/threonine kinase, the rice ( Oryza sativa) protein XA21 confers resistance to a broad spectrum of Xanthomonas oryzae pv. oryzae ( Xoo) races that cause bacterial blight disease. We report here that XA21 binding protein 25 ( XB25) belongs to the plant-specific ankyrin-repeat ( PANK) family. XB25 physically interacts, in vitro, with the transmembrane domain of XA21 through its N-terminal binding to transmembrane and positively charged domain ( BTMP) repeats. In addition, XB25 associates with XA21 in planta. The downregulation of Xb25 results in reduced levels of XA21 and compromised XA21-mediated disease resistance at the adult stage. Moreover, the accumulation of XB25 is induced by Xoo infection. Taken together, these results indicate that XB25 is required for maintaining XA21-mediated disease resistance. [ABSTRACT FROM AUTHOR]