Ding Hao, Hynes Michael F
Department of Biological Sciences, University of Calgary, AB, Canada.
Can J Microbiol. 2009 Aug;55(8):917-27. doi: 10.1139/w09-056.
Rhizobia are agriculturally important bacteria that can form nitrogen-fixing nodules on the roots of leguminous plants. Agricultural application of rhizobial inoculants can play an important role in increasing leguminous crop yields. In temperate rhizobia, genes involved in nodulation and nitrogen fixation are usually located on one or more large plasmids (pSyms) or on symbiotic islands. In addition, other large plasmids of rhizobia carry genes that are beneficial for survival and competition of rhizobia in the rhizosphere. Conjugative transfer of these large plasmids thus plays an important role in the evolution of rhizobia. Therefore, understanding the mechanism of conjugative transfer of large rhizobial plasmids provides foundations for maintaining, monitoring, and predicting the behaviour of these plasmids during field release events. In this minireview, we summarize two types of known rhizobial conjugative plasmids, including quorum sensing regulated plasmids and RctA-repressed plasmids. We provide evidence for the existence of a third type of conjugative plasmid, including pRleVF39c in Rhizobium leguminosarum bv. viciae strain VF39SM, and we provide a comparison of the different types of conjugation genes found in members of the rhizobia that have had their genomes sequenced so far.
根瘤菌是一类对农业具有重要意义的细菌，能够在豆科植物的根部形成固氮根瘤。农业上应用根瘤菌接种剂对于提高豆科作物产量具有重要作用。在温带根瘤菌中，参与结瘤和固氮的基因通常位于一个或多个大质粒（共生质粒）或共生岛上。此外，根瘤菌的其他大质粒携带对根瘤菌在根际的存活和竞争有益的基因。因此，这些大质粒的接合转移在根瘤菌的进化过程中起着重要作用。所以，了解根瘤菌大质粒的接合转移机制为在田间释放事件中维持、监测和预测这些质粒的行为提供了基础。在本综述中，我们总结了两种已知的根瘤菌接合质粒，包括群体感应调控质粒和RctA抑制质粒。我们提供了第三种接合质粒存在的证据，包括豌豆根瘤菌蚕豆生物型VF39SM菌株中的pRleVF39c，并对目前已完成基因组测序的根瘤菌成员中发现的不同类型的接合基因进行了比较。
