水稻黄单胞菌黄色素合成相关基因的克隆与鉴定

用硫酸二乙酯(DES)诱变水稻白叶枯病菌(Xanthomonas oryzae pv. oryzae，简称Xoo)和条斑病细菌(Xanthomonas oryzae pv. oryzicola, 简称Xooc)，分别得到5株和13株黄色素缺失突变体，其中来自Xooc的M6和M12 还丧失了对水稻的致病性和在烟草上激发过敏反应的能力。以Xooc黄色素缺失突变体M51为受体菌交叉互补从Xoo JXOIII基因文库中筛选出一个黄色素合成相关的基因克隆pA341，以Xoo黄色素缺失突变体M1071为受体菌，从Xooc RS105基因文库中获得了一个黄色素合成相关的基因克隆pA270。功能互补显示，18株黄色素缺失突变体中的10株能分别被pA341和 pA270互补后正常产生黄色素，但这两个克隆不能同时互补同一株黄色素缺失突变体。能被pA341互补的黄色素缺失突变体M6没有恢复对水稻的致病性和在烟草上激发过敏反应，表明黄色素合成相关基因与hrp基因间不存在相关性。斑点杂交结果表明，pA270与pA341之间没有同源性。pA270亚克隆结果显示，与黄色素合成相关的基因约11.6kb大小，以基因簇的形式存在，不仅决定了黄色素的产生，还影响黄色素合成的数量和质量（吸收峰）。在紫外光条件下，黄色素能够提高菌体的存活率，提示黄色素对病原细菌有保护作用。

Cloning and Characterization of a Xanthomonadin Gene Cluster from Xanthomoinas oryzae pv. oryzicola

A novel gene pig H had been identified from Xanthomonas oryzae pv. oryzae(Xoo) gDNA library clone pA341 previously. This paper reports a xanthomonadin biosynthetic ( pig ) gene cluster from Xanthomonas oryzae pv. oryzicola(Xooc) . Five pigment minus mutants from Xoo and thirteen from Xooc were obtained by diethyl sulfate (DES) mutagensis. The mutants M6 and M12 failed to cause disease in rice and induce the HR in tobacco either. One clone pA270 was screened from Xooc RS105 gDNA library after all individual clone was transferred into a mutant M1071 Clony blot hybridization displayed that the foreign NDA fragment harbored in pA341 was not homologous to that in pA270 Moreover, only 10 of the above 18 xanthomonadin mutants were restored to produce xanthomonadin by either pA341 or pA270 clone. This demonstrated that the mutated sites in the above 18 xanthomonadin were different and might not be in a same gene locus. Subclones of a 11 6kb Eco RI fragment affected either the amount or absorption spectra of pigment production, which indicated that this fragment encoded various functional fragments and was possibly a gene cluster. The roles of the pigment in protecting the bacterial cells from damage by UV radiation suggested that the pigment contribute to the survival of the pathogens during their colonization in rice.