The Xa1 gene in rice confers resistance to Japanese race 1 of Xanthomonas oryzae pv. oryzae, the causal pathogen of bacterial blight (BB). We isolated the Xa1 gene by a map-based cloning strategy. The deduced amino acid sequence of the Xa1 gene product contains nucleotide binding sites (NBS) and a new type of leucine-rich repeats (LRR); thus, Xa1 is a member of the NBS-LRR class of plant disease-resistance genes, but quite different from Xa21, another BB-resistance gene isolated from rice. Interestingly, Xa1 gene expression was induced on inoculation with a bacterial pathogen and wound, unlike other isolated resistance genes in plants, which show constitutive expression. The induced expression may be involved in enhancement of resistance against the pathogen.
水稻Xa1是抗白葉枯病菌日本小種1號的抗病基因，該病原菌是引起細菌性白葉枯病的發(fā)病病原菌。我們通過圖位克隆的方法分離到了Xa1基因。Xa1的氨基酸序列含有核苷酸結合位點(NBS)和一個新型的富含亮氨酸重復序列(LRR)，因此Xa1是植物NBS-LRR類抗病基因，但不同于另外一個水稻白葉枯病抗病基因Xa21。有趣的是Xa1受接種細菌性病原體和機械損傷誘導表達，這與已分離的組成性表達的抗病基因不同。Xa1這種誘導表達可能與提高對病原菌的抗性有關。