EXPRESSION OF XA1, A BACTERIAL BLIGHT-RESISTANCE GENE IN RICE, IS INDUCED BY BACTERIAL INOCULATION

The Xa1 gene in rice confers resistance to Japanese race 1 of Xanthomo nas oryzae pv. oryzae, the causal pathogen of bacterial blight (BE). W e isolated the Xa1 gene by a map-based cloning strategy. The deduced a mino acid sequence of the Xa1 gene product contains nucleotide binding sites (NBS) and a new type of leucine-rich repeats (LRR); thus, Xa1 i s a member of the NBS-LRR class of plant disease-resistance genes, but quite different from Xa21, another BB-resistance gene isolated from r ice. Interestingly, Xa1 gene expression was induced on inoculation wit h a bacterial pathogen and wound, unlike other isolated resistance gen es in plants, which show constitutive expression. The induced expressi on may be involved in enhancement of resistance against the pathogen.