Abstract: 【Objective】The objective of this study is to analyze the structure of SSMP (salt-sensitive membrane protein), understand the expressing characteristics of SSMP, predict and analyze the function of SSMP in the process of stress resistance in Arabidopsis thaliana. 【Method】 The structure of SSMP protein was analyzed using bioinforatics method. Real-time PCR was adopted to analyze the temporal and spatial expression of SSMP in Arabidopsis. Preliminary analysis of the subcellular localization of SSMP was performed through the establishment of SSMP-GFP fusion expression vector and protoplast transformation. The tissue localization carrier was established with SSMP promoter connecting GUS reporter gene to analyze the tissue localization of SSMP. To determine the function of SSMP protein, overexpression experiments were performed in Col-0 Arabidopsis. Full-length cDNA was cloned into a binary vector downstream of the SSMP 35S promoter, and the construct was transformed into Col-0 Arabidopsis. Three lines positive seedlings of the transgenic Arabidopsis of over-expression of SSMP were obtained using Real-time PCR analysis. The phenotype and the stress tolerance of the transgenic Arabidopsis over-expression of SSMP were analyzed and so the biological function of SSMP gene could be understand. The cell membrane permeability was compared between wild type and the transgenic Arabidopsis over-expression of SSMP, the data of the cell membrane permeability was detected by the conductance instrument. The function of SSMP in the stress resistance process of Arabidopsis was analyzed.【Result】SSMP is a funtion unknown protein, it has 411 amino acids, containing a START conserved domain(the lipid/sterol-binding StAR-related lipid transfer protein domains). Bioinformatics analysis showed that SSMP has a phosphatidylcholine binding site, START domain could combine with lipids and sterols and transports cholesterol to inner membrane, so SSMP may influence the membrane components and play a role in the process of plant resistance. In this study, the expression level of SSMP in the tissues or organs of Arabidopsis was analyzed by using real-time PCR technique, andthe results showed that the order of the expression level of SSMP in Arabidopsis organs was stem leaf, cauline leaf, stem, root, flower and seed. Under normal circumstances, GUS is mainly expressed in hypocotyls, the cotyledon and true leaf veins and epidermal hairs. After treatment with 50 mmol·L^-1 NaCl, the expression of GUS in hypocotyls and cotyledons showed no significant changes, but the expression of GUS in true leaf were decreased. After treatment with 100 mmol·L^-1 NaCl, the expression of GUS was significantly reduced in the hypocotyl, cotyledon and true leaf, indicating that the expression of SSMP inhibited by NaCl. Preliminary analysis of the subcellular localization of SSMP was performed through the establishment of SSMP-GFP fusion expression vector and protoplast transformation and observed the fluorescence under 488nm wavelength using laser scanning confocal microscope. The result showed that SSMP was mainly localized on cytoplasma membrane. The cell membrane permeability of the transgenic Arabidopsis leaves of over-expression of SSMP was higher than that of the wild type. The expression of SSMP was inhibited and the germination of the seeds of SSMP function-gaining transgenic plants was lower obviously than wild type in the medium containing NaCl. 【Conclusion】SSMP is a protein of 411 amino acids with phosphatidylcholine binding sites, containing a START domain, mainly located on the cytoplasmic membrane, expressed in various tissues of Arabidopsis thaliana plants, especially the highest expression level in leaves. The expression of SSMP mainly localized in the genesis areas of leaf vein and epidermal hair. The expression of SSMP was inhibited by salt stress. The cell membrane permeability increased and the salt tolerance decreased in Arabidopsis overexpressing SSMP.

Key words: Arabidopsis, SSMP, structure analysis, expression characteristics, salt resistance