Identification Of Arabidopsis Glucosyltransferase Genes Involved In Plant Salt Tolerance

Salt tolerance of plant is involved in a complex series of physiological and biochemical reactions or processes, and it is often the result of interactions among multiple genes. Until now what we have found may simply reflect some aspects of the whole salt-tolerant mechanisms of plants. Studying the plant salt tolerance from a new angle could help us to better understand plant salt tolerance mechanisms in a comprehensive level, and it is possible to lay a solid theoretical basis for improving the salt tolerance of crops in their whole growth cycle.Glycosyltransferases are one family of enzymes for catalyzing the glycosylation of molecules. They are important in regulating metabolic balance of plant cells and maintaining the growth and development of plants. Recently, glycosyltransferase genes were reported involved in enhancing the ability of plant disease resistance, but it was unkown that whether glycosyltransferases were involved in the abiotic stresses. This research carried out the analysies of glycosyltransferase genes involved in plant salt tolerance, and two glycosyltransferase genes were identified to be related to the salt-stress response. Furthermore, a glycosyltransferase gene involved in the flowering time was found and a preliminary investigation was made. The main results achieved in this research were summarized as follows:1. Two salt-induced glycosyltransferase genes were determined.Through the salt treatment and RT-PCR methods, the expressions of glycosyltransferase genes of Arabidopsis thaliana Col-0 were analysed. Two salt-induced glycosyltransferase genes, UGT85A5 and UGT91A1, were determined.2. Three salt tolerance candidate genes of glycosyltransferases were cloned and their genetic transformations were completed. Using RT-PCR method, three salt tolerance candidate genes of glycosyltransferases were cloned, their plant expression vectors were constructed. UGT85A5 and UGT87A2 over-expressing transgenic Arabidopsis and tobacco plants were obtained respectively, and the UGT91A1 overexpressing transgenic tobacco plants were also obtained using Agrobacterium infection method.3. The salt tolerant of over-expression transgenic plants were analysed and two glycosyltransferase genes involved in salt tolerant responses of plants were identified.According to the salt tolerance test of UGT85A5 and UGT87A2 overexpression transgenic tobacco plants, it was found that those transgenic plants of both glycosyltransferases exhibited salt-tolerant phenotype.The salt-tolerant physiological indexes of UGT85A5 transgenic tobacco plants were measured. The results showed that Na+/K+ ratio in leaves of the transgenic tobacco was higher than that of wild-type tobacco on normal growth conditions, while after the treatment of 150mM NaCl, the rate of increase of Na+/K+ ratio in leaves of transgenic tobacco was significantly lower than that of wild type tobacco, indicating that the transgenic tobacco accumulated less Na+ than the wild-type under salt stress. The measurement of the content of malondialdehyde (MDA) under salt stress showed that the rising of MDA content in transgenic tobacco leaves was significantly lower than that of wild-type, and the MDA content in transgenic tobacco leaves was 11 lower than wild-type. The determination of content of soluble sugar showed that transgenic tobacco leaves accumulated much more soluble sugar than wild-type under salt stress, with a 9% higher content of soluble sugar in transgenic tobacco than in the wild type.UGT87A2 mutant of Arabidopsis showed salt-sensitive phenotype than the wild type when cultured horizontally and vertically. The salt-tolerant physiological indexes of UGT87A2 transgenic tobacco plants were also measured. The results showed that the rising of MDA content in transgenic tobacco leaves was significantly (34%) lower than that of wild-type under salt stress. The determination of soluble sugar showed that transgenic tobacco leaves accumulated much more soluble sugar, with a 13% higher content of soluble sugar in transgenic tobacco than in the wild type under salt stress.4. The glycosyltransferase gene UGT87A2 involved in plant flowering time was first found and the preliminary expression analysis of flowering-related genes in mutants was made.It was found that Arabidopsis mutant of UGT87A2 gave a late bolting phenotype whether under long day or short day. The mutant phenotypes also included large seeds, large and dark leaves, and long growth cycle.The expression of flowering-related genes CO, FLC, FT, API, LFY and SOC1 were analysed in UGT87A2 mutant. The results showed that the expression level of FLC, an inhibitor of flowering, was much higher in mutant than that of wild-type at bolting. Other flowering-related genes such as FT, API and LFY all of which promote flowering, were given a significantly reduced expression level in mutant than that of the wild type. These results suggested that UGT87A2 gene likely affected the flowering gene expression by some unkown mechanism, thus resulting in late flowering.In summary, this research provided the preliminary evidences for the functions of glycosyltransferase genes UGT85A5 and UGT87A2 in plant salt tolerance, and the UGT87A2 gene was for the first time found to be involved in plant flowering regulation. To get more knowledge about the mechanisms how the two glycosyltransferase genes exert their roles, further exploration need to be made.