Departamento de Microbiología, Facultad de Ciencias, Instituto de Hortofruticultura Subtropical y Mediterránea "La Mayora"-Universidad de Málaga-Consejo Superior de Investigaciones Científicas (IHSM-UMA-CSIC), Universidad de Málaga, Campus de Teatinos, 29071 Málaga, Spain.
BMC Microbiol. 2014 Feb 21;14:46. doi: 10.1186/1471-2180-14-46.
The antimetabolite mangotoxin is a key factor in virulence of Pseudomonas syringae pv. syringae strains which cause apical necrosis of mango trees. Previous studies showed that mangotoxin biosynthesis is governed by the mbo operon. Random mutagenesis led to the identification of two other gene clusters that affect mangotoxin biosynthesis. These are the gacS/gacA genes and mgo operon which harbors the four genes mgoBCAD.
The current study shows that disruption of the nonribosomal peptide synthetase (NRPS) gene mgoA resulted in loss of mangotoxin production and reduced virulence on tomato leaves. Transcriptional analyses by qPCR and promoter reporter fusions revealed that mbo expression is regulated by both gacS/gacA and mgo genes. Also, expression of the mgo operon was shown to be regulated by gacS/gacA. Heterologous expression under the native promoter of the mbo operon resulted in mangotoxin production in non-producing P. syringae strains, but not in other Pseudomonas species. Also introduction of the mbo and mgo operons in nonproducing P. protegens Pf-5 did not confer mangotoxin production but did enhance transcription of the mbo promoter.
From the data obtained in this study, we conclude that both mbo and mgo operons are under the control of the gacS/gacA two-component system and that the MgoA product acts as a positive regulator of mangotoxin biosynthesis.
抗代谢物芒果毒素是导致芒果树顶坏死的丁香假单胞菌 pv. 丁香假单胞菌菌株毒力的关键因素。先前的研究表明，芒果毒素的生物合成受 mbo 操纵子控制。随机诱变导致了另外两个影响芒果毒素生物合成的基因簇的鉴定。这些是 gacS/gacA 基因和 mgo 操纵子，它包含四个基因 mgoBCAD。
本研究表明，非核糖体肽合成酶（NRPS）基因 mgoA 的破坏导致芒果毒素的产生丧失和对番茄叶片的毒力降低。通过 qPCR 和启动子报告融合的转录分析表明，mbo 的表达受 gacS/gacA 和 mgo 基因的调节。此外，mgo 操纵子的表达受 gacS/gacA 调节。在 mbo 操纵子的天然启动子下进行的异源表达导致非产芒果毒素的丁香假单胞菌菌株产生芒果毒素，但在其他假单胞菌属中则没有。此外，将 mbo 和 mgo 操纵子引入非产芒果毒素的 P. protegens Pf-5 中并没有赋予芒果毒素的产生，但确实增强了 mbo 启动子的转录。
从本研究获得的数据中，我们得出结论，mbo 和 mgo 操纵子都受 gacS/gacA 双组分系统的控制，并且 MgoA 产物作为芒果毒素生物合成的正调节剂。
