Recombinant expression of an autoinducer synthase of Sinorhizobium sp.1128 in Escherichia coli

Abstract:

[Objective] To explore the roles of quorum sensing system in establishing symbiosis between bacterium Sinorhizobium sp.1128 and its plant host Melilotus suaveolens Ledeb. [Methods] According to homologous analysis, we designed primers to amplify the autoinducer synthase encoding genes in Sinorhizobium sp.1128 according to Sinorhizobium medicae WSM419 genome sequences. The autoinducer synthase encoding genes were cloned into the expression vector of pYC12 and expressed in E. coli DH5a. Thin-layer chromatography ( TLC) assay was used to study their roles in autoinducer production. A duplicated inactivation of the gene was used to explore its function in plant nodulation. [Re-sults]Homologous analysis showed that at least three annotated acylated homoserine lactone (AHL) synthase genes ex-isted in Sinorhizobium medicae WSM419 genome. We cloned these three autoinducer synthase genes in Sinorhizobium sp.1128. One of these genes named traI2 was over expressed in E. coli DH5α. At least two different AHLs were produced by the recombinant strain. Disruption of traI2 reduced both the autoinducers (AI) activities and AHL production by TLC detection. Furthermore, the complementation of traI2 reverted the phenotype of AI activities. These findings demonstrate that traI2 was responsible for AI synthesis in Sinorhizobium sp.1128. More important, the traI2 deficient strains were defective in nodule formation on their host plant. [Conclusion] The quorum sensing circuits in Sinorhizobium sp.1128 may play an important role in symbiosis between plant and bacterium.