An Oxidoreductase Is Involved in Cercosporin Degradation by the Bacterium Xanthomonas campestris pv. zinniae
An Oxidoreductase Is Involved in Cercosporin Degradation by the Bacterium Xanthomonas campestris pv. zinniae
复制标题
氧化还原酶参与野油菜黄单胞菌 pv. 细菌对尾孢菌素的降解。
DOI：
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发表时间：
2006
影响因子：
4.4
通讯作者：
M. E. Daub
中科院分区：
文献类型：
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作者：
Tanya. Taylor;T. Mitchell;M. E. Daub
聚酮类毒素cercosporin在Cercospora属真菌的发病过程中起关键作用。油菜黄单胞菌pv。百日草能够迅速降解这种毒素。油菜的生长。百日菌菌株在含头孢菌素的培养基中导致头孢菌素的分解，并形成一种无毒的分解产物——黄孢酸。采用甲磺酸乙酯诱变方法，对一株快速降解虫孢素的菌株（XCZ-3）进行了5个不降解虫孢素的突变体，并用野生型菌株的基因组文库进行了转化。所有五个突变体都与相同的基因组克隆互补，该基因组克隆编码一个假定的转录调节因子和一个氧化还原酶。这两个基因的同时表达是补充突变表型所必需的。突变体序列分析表明，5个突变体氧化还原酶基因均存在点突变，而调节基因无突变。定量反转录pcr （RT-PCR）结果显示，暴露于cercosporin后，这两个基因在野生型菌株中的表达上调。将氧化还原酶和转录调节基因转化到三种非头孢菌素降解细菌中，以确定它们是否足以降解头孢菌素。定量RT-PCR分析证实氧化还原酶在所有转偶联物中均有表达。然而，没有一种转偶联物能够降解头孢菌素，这表明需要其他因素来降解头孢菌素。葡萄球菌菌丝孢素降解的进一步研究。百日菊可以通过使用一套基因来改造抗虫的植物。
ABSTRACT The polyketide toxin cercosporin plays a key role in pathogenesis by fungal species of the genus Cercospora. The bacterium Xanthomonas campestris pv. zinniae is able to rapidly degrade this toxin. Growth of X. campestris pv. zinniae strains in cercosporin-containing medium leads to the breakdown of cercosporin and to the formation of xanosporic acid, a nontoxic breakdown product. Five non-cercosporin-degrading mutants of a strain that rapidly degrades cercosporin (XCZ-3) were generated by ethyl methanesulfonate mutagenesis and were then transformed with a genomic library from the wild-type strain. All five mutants were complemented with the same genomic clone, which encoded a putative transcriptional regulator and an oxidoreductase. Simultaneous expression of these two genes was necessary to complement the mutant phenotype. Sequence analysis of the mutants showed that all five mutants had point mutations in the oxidoreductase gene and no mutations in the regulator. Quantitative reverse transcription-PCR (RT-PCR) showed that the expression of both of these genes in the wild-type strain is upregulated after exposure to cercosporin. Both the oxidoreductase and transcriptional regulator genes were transformed into three non-cercosporin-degrading bacteria to determine if they are sufficient for cercosporin degradation. Quantitative RT-PCR analysis confirmed that the oxidoreductase was expressed in all transconjugants. However, none of the transconjugants were able to degrade cercosporin, suggesting that additional factors are required for cercosporin degradation. Further study of cercosporin degradation in X. campestris pv. zinniae may allow for the engineering of Cercospora-resistant plants by using a suite of genes.