Stress Evaluation Of SsBHMT Transgenic Arabidopsis Plants And Expression Analysis Of Maize S-adenosylmethionin Synthetase Gene Family Members

Methionine is an essential amino acid, Mammals do not produce methionine de novo. The level of methionine often limits the nutritional value of crop plants. Apart from its role as a protein constituent and its central role in the initiation of mRNA translation, methionine indirectly regulates a variety of cellular processes.Betaine-homocysteine-S-methyltransferase(SsBHMT), In animals, this enzyme can catalyze betaine to form methionine. At present, plant has not yet been found this gene. In plants,methionine is not only a fundamental metabolite, but also as the substrate of S-adenosylmethionin synthetase (SAMS) participates in S-adenosylmethionine (SAM) synthesis. SAM is the primary biological methyl group donor, which participates in both primary and secondary metabolism. Examples include lipids, DNA, RNA, proteins, alkaloids, phytosterols, chlorophyll, lignins, suberins and so on. Therefore, we analyed the resistance of SsBHMT transgenic Arabidopsis and the expression of S-adenosylmethionin synthetase gene. It provided theoretical basis for studying the synthesis of methionine and metabolic mechanisms in plants, improve the resistance of plants.The main results were shown as follows:1. Expression of the SsBHMT in transgenic plants was determined by RT-PCR. Wild type didn't amplify SsBHMT gene.2. Under mannitol and salt stress, the germination rate of transgenic plants were superior to wild type. Transgenic plants were 1.6 times than wild type at 100mmol/L mannitol; transgenic plants were 2.6 times than wild type at 100mmol/L NaCl. Under normal condition and mannitol stress, the root length and root density were greater than wild type, more lateral roots than wild type. Under drought stress, the survival rate of transgenic plants was greater than wild type. We observed the physiological indexes, chlorophyll content. The result showed that transgenic plants had much higher chlorophyll content than wild type, under salt stress. At high NaCl concentration, the activity of SOD was higher than wild type. The contents of MDA increased remarkably with the increase of NaCl concentration for wild type. Transgenic plants increased at first and then decreased. This was almost opposite trend to the activity of SOD. These results evidenced the transform of SsBHMT effectively increased the resistance of transgenic plants. 3. All of the four maize SAMS genes family members were expressed both under normal and salt conditions. In the control seedlings, the mRNA levels of the four genes were higher in roots and stems than those in leaves. Under the salt stress, the expression of SAMS1 was down-regulated in stems, up-regulated in leaves, but no change in roots. The transcript levels of SAMS2 and SAMS4 also increased significantly under salt stress. However, SAMS3 had no response to NaCl in any organs.4. The bisulfite sequencing method was used to detect the methylation pattern of the promoter region of SAMS in two different kinds of maize allied leaves. The result showed that H04-36 and Y52 were both non-methylated.