Approximately one third of the identified 34 rice major disease resistance (R) genes conferring race‐specific resistance to different strains of Xanthomonas oryzae pv. oryzae (Xoo), which causes rice bacterial blight disease, are recessive genes. However, only two of the recessive resistance genes have been characterized thus far. Here we report the characterization of another recessive resistance gene, xa25, for Xoo resistance. The xa25, localized in the centromeric region of chromosome 12, mediates race‐specific resistance to Xoo strain PXO339 at both seedling and adult stages by inhibiting Xoo growth. It encodes a protein of the MtN3/saliva family, which is prevalent in eukaryotes, including mammals. Transformation of the dominant Xa25 into a resistant rice line carrying the recessive xa25 abolished its resistance to PXO339. The encoding proteins of recessive xa25 and its dominant allele Xa25 have eight amino acid differences. The expression of dominant Xa25 but not recessive xa25 was rapidly induced by PXO339 but not other Xoo strain infections. The nature of xa25‐encoding protein and its expression pattern in comparison with its susceptible allele in rice–Xoo interaction indicate that the mechanism of xa25‐mediated resistance appears to be different from that conferred by most of the characterized R proteins.
目前在水稻中鑒定出有34個具有對不同水稻黃單胞菌株主效的R小種?；剐曰?，它們中有大約三分之一是隱性的。到目前僅有2個隱性抗性基因被克隆。本文中我們報道另外一個具有對水稻白葉枯病菌具有隱性抗性的基因xa25。x25位于水稻12號染色體的著絲粒區(qū)域，在水稻苗期和成熟期對黃單胞菌株P(guān)XO339具有小種?；剐?，即能抑制水稻黃單胞菌株的生長。該基因編碼一個屬MtN3/saliva家族的蛋白，在真核生物中，包括哺乳動物中普遍存在。顯性的Xa25基因轉(zhuǎn)到一個攜有隱性xa25的抗性水稻植株中發(fā)現(xiàn)水稻喪失對菌株P(guān)XO339的抗性。隱性xa25和顯性Xa25各自編碼的蛋白具有8個氨基酸的差異，在不同的水稻黃單胞菌株中只有PXO339能迅速誘導(dǎo)Xa25的表達，而不能誘導(dǎo)隱性的xa25基因表達。在水稻-白葉枯病菌互作中，xa25編碼蛋白的屬性和表達模式與其易感等位基因的對比，表明xa25介導(dǎo)的抗性似乎與其他已鑒定R蛋白抗性機制不同。