Abstract: An EcoRⅠ-BamHⅠ DNA, corresponding to the coding region NLS (nuclear localization signal) and AD (acidic transcriptional activation domain) of AvrXa3 of Xanthomonas oryzae pv. oryzae (Xoo), was used as a probe to screen the genomic library of Xanthomonas oryzae pv. oryzicola(Xooc). One avrBs3/PthA gene clone was obtained after positive clones of the library were digested by EcoRⅠ endoenzyme and proved by Southern blot. Sequencing subclone, pPth13, indicated that it contained a gene belonging to the avrBs3/PthA family of Xanthomonas pathogenic bacteria, and was nominated as avr/pth13 gene. As other AvrBs3/PthA, the putative protein of avr/pth13 gene possesses the same 5’- and 3’- terminals, one leucine zipper (LZ), three NLSs and one AD. However, the difference of the gene with other avrBs3/PthA family members was the repeat numbers of 34 amino acid unit coded by 102 bp repeat. The 102 bp unit was repeated 5.5 times in avr/pth13 gene. Blasting the sequence in GenBank database showed that avr/pth13 gene was the smallest in avrBs3/PthA family. (Alignment) of 12-13th residues in 34 amino acid unit of Avr/Pth13 with those of other AvrBs3/PthA proteins demonstrated that at least three HD(His and Asp) residues in 12-13th position of 34 amino acid unit might be necessary for avirulence or/and virulence. Pathogenicity tests of strain PXO99A containing avr/pth13gene on near isogenic lines (NILs) of rice showed that avr/pth13 gene strengthened the virulence of Xoo on the tested NILs. All the above confirmed that avrBs3/PthA gene(s) existed in Xooc as that in Xoo, determining virulence in bacterial streak and blight diseases of rice.

Key words: Xanthomonas oryzae pv. oryzicola

摘要： 用水稻白叶枯病菌（Xanthomonas oryzae pv. oryzae, Xoo）无毒基因avrXa3对应的核定位信号（Nuclear localization signal, NLS）和酸性转录活化域（Acidic transcriptional activation domain, AD）的DNA片段构建探针，筛选水稻条斑病细菌（X.o.pv.oryzicola, Xooc）基因文库，获得avrBs3/PthA家族基因阳性克隆p13。序列测定和分析结果显示，avr/pth13基因长度为2268 bp，编码755氨基酸，与avrBs3/PthA家族其他成员一样，具有几乎一样的5’端和3’端、1个亮氨酸拉链（Leucine zipper, LZ）、3个NLS和1个AD区域，不同的是102 bp重复单元的重复数为5.5。蛋白质水平上同列比较发现，Avr/Pth13中第3、4和5个34氨基酸重复单元的第12和第13位氨基酸均为HD（组氨酸和天冬氨酸），蛋白质的C端没有SGSVGGTI残基。目前avr/pth13基因是该家族的最小成员。将avr/pth13基因导入Xoo菌株PXO99A中，在水稻近等基因系上致病性测定结果显示，avr/pth13基因增强了Xoo的致病能力。以上结果证实，水稻条斑病细菌与水稻白叶枯病菌一样，都存在avrBs3/PthA家族基因，决定着Xooc的毒性或/和无毒性。

关键词: 水稻条斑病细菌, 基因, 毒性, 致病性