%D 2004 %0 ARTICLE %T Isolation and characterization of rice mutants compromised in Xa21-mediated resistance to X oryzae pv . oryzae . %J Theor . Appl . Genet . %V 108 ( 3 ) %P 379-84 %A Wang GL %A Wu C %A Zeng L %A He C %A Baraoidan M %A de Assis %A Goes da %A Silva F %A Williams CE %A Ronald PC %A Leung H %M pub14523518 %X The rice gene , Xa21 , confers resistance to diverse races of Xanthomonas oryzae pv . oryzae ( Xoo ) and encodes a receptor-like kinase with leucine-rich repeats in the extra-cellular domain . To identify genes essential for the function of the Xa21 gene , 4 , 500 IRBB21 ( Xa21 isogenic line in IR24 background ) mutants , induced by diepoxybutane and fast neutrons , were screened against Philippine race six ( PR6 ) Xoo for a change from resistance to susceptibility . From two greenhouse screens , 23 mutants were identified that had changed from resistant to fully ( 6 ) or partially ( 17 ) susceptible to PR6 . All fully susceptible mutants carried rearrangements at the Xa21 locus as detected by PCR and Southern hybridization . For the partially susceptible mutants , no changes were detected at the Xa21 locus based on Southern and PCR analyses . However , two of these mutants were confirmed via genetic analysis to have mutations at the Xa21 locus . Partially susceptible mutants exhibited variation in level of susceptibility to different Xoo strains , suggesting that they may carry different mutations required for the Xa21-mediated resistance . The mutants identified in this study provide useful materials for dissecting the Xa21-mediated resistance pathway in rice .