Rhizobia are nitrogen-fixing symbionts of plants. Their genomes frequently contain large plasmids, some of which are able to perform conjugative transfer. Plasmid pSfr64a from Sinorhizobium fredii GR64 is a conjugative plasmid, whose transfer is regulated by quorum sensing genes encoded by itself (traR64a, traI64a), in the symbiotic plasmid pSfr64b (traR64b, traI64b), and in the chromosome (ngrI). Also, transfer of pSfr64b requires quorum sensing elements encoded in this plasmid (traR64b, traI64b), in pSfr64a (traR64a), and in the chromosome (ngrI). These results demonstrate that pSfr64a and the symbiotic plasmid depend on each other for conjugative transfer. Plasmid pSfr64a from S. fredii GR64 is unable to transfer from the genomic background of Rhizobium etli CFN42. Our results show that the relaxase of pRet42a is able to process the oriT of pSfr64a, and viceversa, underlining their functional similarity and suggesting that in addition to the external signals, the "cytoplasmic environment" may pose a barrier to plasmid dissemination, even if the plasmids are functional in other aspects.

中文翻译：

---

费氏中华根瘤菌GR64的质粒pSfr64a和共生质粒pSfr64b通过群体感应元件控制彼此的结合转移。

根瘤菌是植物的固氮共生体。他们的基因组通常包含大型质粒，其中一些能够进行结合转移。来自费氏中华根瘤菌GR64的质粒pSfr64a是一种共轭质粒，其转移受到自身编码的群体感应基因（traR64a，traI64a），共生质粒pSfr64b（traR64b，traI64b）和染色体（ngrI）的调控。同样，pSfr64b的转移需要在该质粒（traR64b，traI64b），pSfr64a（traR64a）和染色体（ngrI）中编码的群体感应元件。这些结果证明pSfr64a和共生质粒彼此依赖于共轭转移。来自弗氏链球菌GR64的质粒pSfr64a不能从根瘤菌CFN42的基因组背景转移。