The Role Of Serratia Plymuthica Quorum Sensing Signals In Plant Development And Tolerance To Stress

Serratia plymuthica strains of HRO-C48 and G3 were isolated from the rhizosphere of oilseed rape and the wheat stem, respectively and displayed biocontrol potential to suppress several plant diseases due to production of chitinases,protease and pyrrolnitrin, as well as promoting plant growth by production of indole-3-acetic acid （IAA）.In this study, the mechanisms underlying plant responses to QS signal molecules was investigated, using plant signal transduction and proteomics technologies, and transgenic Arabidopsis thaliana carrying splI/R and spsI/R genes,which consist of two quorum sensing （QS） systems in S. plymuthica G3.The major results achieved in detail are as follows:1.Low concentration of AHL（N-oxo-hexanoyl homoserine lactone） signal molecules, which is the major QS signals in both strains HRO-C48 and G3,not only can promote plant growth and development, but also improve the tolerance to stress of ABA and NaCl in Arabidopsis thaliana and rice.2. Using transgenic Arabidopsis seedlings containing the IAA-responsive DR5::GUS fusion, followed by GUS staining and showed that the IAA content increased in all growing points of the seedlings after treatment with AHL signal molecule.Fluorescence detection the response of Arabidopsis thaliana and rice seedlings to AHL signaling molecules and revealed that the content of H2O₂ and NO increased in both of them, compared with the control treatment.3.The Experiments of mung bean adventitious roots suggested that H2O₂ as the secondary messanger is required for IAA-mediated stimulate plant growth after treatment with AHL4.Comparative proteomics analysis of the Arabidopsis thaliana seedlings between the treatments with and without AHL, we found that 121 differential expression protein spots and identified 47 proteins successfully by MALDI-TOF mass spectrometry. Among them, Arabidopsis seedlings with AHL treatment contained 31 up-regulated spots and 17 down-regulated spots.Mainly including gene transcriptional-related proteins,such as operon ArsR; a lot of modification, conversion, and chaperon proteins, such as antioxidant reductase, methylthio-D acid reductase, dnaK molecular chaperone, etc.;signal transduction proteins, PAS/PAC-sensitive signal transduction histidine kinase; metabolism-related proteins,such as the ribulose phosphate kinase, FOF1 ATP synthaseβ; and photosynthesis-related proteins, such as the conversion of oxygen-related protein, chlorophyllα/β-binding protein.5.Comparative proteomics analysis of the rice seedlings between the treatments with and without AHL, we found that 206 differential expression protein spots in root and identified 96 proteins successfully by MALDI-TOF mass spectrometry. Among them, rice seedlings with AHL treatment contained 58 up-regulated spots and 38 down-regulated spots.We found 155 differential expression protein spots in leaves and identified 31 proteins successfully by MALDI-TOF mass spectrometry, containing 11 up-regulated spots and 19 down-regulated spots compared with control. Mainly including gene transcriptional-related protein, such as the cold shock protein in root, transcription terminator in leaves;translation and ribosomal protein, transcription initiation factors,such as the roots, leaves with the 40S ribosomal protein SA; modification, conversion, and chaperon proteins,such as heat shock proteins 90 and so on;cell wall,cell membrane formation associated protein, such as rice roots with isoprene related protein; signal transduction proteins,such as the protein kinase in root;a large number of metabolic protein, such as zinc transporter in rice roots, and ATP synthase, quinone synthesis of enzymes aminopeptidase N,1,5 diphosphate carboxylase, etc. in leaves;photosynthesis-related proteins in rice leaves light system, such as chloroplast-related protein; more over there is a lot of formation and organization of related proteins in rice root, such as micro tubes a, tubulin P,1,3-βglucan enzymes.6.splI/R and spsR/I consisting of two QS systems were cloned from Serratia plymuthica G3 Respectively. splI/R and spsR/I genes were transferred by Agrobacterium tumefaciens into Arabidopsis thaliana in order to observe the phenotypes of transgenic plants and assay the biological control-related traits,aims to better understanding how the host plants sense and response to the QS signals by the biocontrol bacteria.We have obtained spll, splR,splR, spsR transgenic seedlings of Arabidopsis.These results above suggest that biocontrol strains of Serratia plymuthica promote plant growth and development is closely correlated with their dominant species of AHL signal.This will help to unravel the molecular mechanism involved in the beneficial interactions between biocontrol S.plymuthica and host plants, as well as optimisition of biocontrol inocula for application.