中文摘要：

白叶枯病菌与水稻间的互作符合基因对基因模式，不同小种中存在特异的avrBs3／pthA家族基因。对中国水稻白叶枯病菌小种C8菌株基因组DNA进行BarnH I酶切和Southern杂交，发现了其特有的约6．0kb大小、含avrBs3／pthA家族基因的信号条带。经文库筛选、Southern杂交和限制性酶切分析，获得了C8小种avr／pthC8a基因。将该基因导入菲律宾小种6的代表菌株PXO99^A中，发现nur／pthC8a可使PXO99^A丧失对水稻品种Asominori（携有成株期抗性基因Xa17）的毒性，暗示avr／pthC8a可能是与Xa17相应的无毒基因。序列分析发现，avr／pthC8a基因大小为3816bp，编码1272个氨基酸，由102bp编码的34个氨基酸重复单元在基因内的重复数为20．5个，其3’端的BamHI酶切位点由GGATCc突变为AGATCC，其他特征均与avrBs3／pthA家族的成员相似，即C端存在1个亮氨酸拉链、3个核定位信号和1个酸性转录激活域。avr／pthC8a基因3’端的BamH I酶切位点发生突变在avrBs3／pthA家族基因中鲜有报道。中国C8小种avr／pthC8a基因的发掘，为进一步了解水稻黄单胞菌毒性变异以及avrBs3／pthA家族基因的进化提供了理论依据。

英文摘要：

The interaction between Xanthomonas oryzae pv. oryzae （Xoo） and rice follows gene-for-gene model. A 6.0 kb particular fragment was identified from a Chinese race C8 strain of Xoo, through screening its genomic library by Southern blot with a highly conserved EcoR J -BamH I fragment of the avrBs3/pthA family as probe. This specific DNA contained an avirulence gene, namely avr/pthC8a, which transmitted the Philippine strain PXO99A from compatible into incompatible interactions with rice Asominori carrying R gene Xa17, suggesting that avr/pthC8a is possibiy corresponding for Xa17 specificity. Sequence analysis showed that avr/pthC8a, 3819 bp in size, is a avrBs3/pthA family member, and the repeat number of the I02 bp repeat unit is 20.5. The structure of the gene is almost as same as those of the avrBs3/pthA family genes at 5＇ and 3＇-terminals. The putative protein has a lucine zipper, three nucleotide location signals and an acid transcriptional activation domain at C-terminal. The novel is that the BarnH I site at 3＇-terminal of the gene is mutagenesis from GGATCC into AGATCC, which has not been reported so far. Thus, identification of avr/pthC8a of Chinese race C8 provides a fundamental understanding of virulence differentiation among different races of Xoo and coevolution of avrBs3/pthA genes with rice.