A catalytically impaired mutant of the rice Xa21 receptor kinase confers partial resistance to Xanthomonas oryzae pv oryzae

The rice Xa21 gene that confers resistance against Xanthomonas oryzae pv oryzae encodes a receptor-like kinase protein consisting of a presumed extracellular domain, a transmembrane domain and a cytoplasmic protein kinase. To determine if the XA21 kinase domain is essential for transducing the defense response, we mutated the Lysine 736 of Xa21 to Glutamic acid (K736E) to construct XA21K736E. Transgenic lines expressing XA21K736E display partial resistance to Xoo PR6. Bacterial growth in the XA21K736E mutants is intermediate to that of transgenic lines expressing the wild type Xa21 gene and the susceptible control, Taipei 309. The partial resistance phenotype was transmitted to the progeny of two independent lines. Thus, although catalytic activity of XA21 is essential for wild type resistance levels, the catalytically impaired mutant maintains partial resistance activity. q 2003 Elsevier Ltd. All rights reserved.