Agrobacterium Tumefaciens-mediated Transformation By Using BADH2-derived RNAi Construct In Rice (Oryza Sativa)

Glycinebetaine is an important compatible solute and accumulated in response to salt, drought and other osmotic stresses in many organisms. It exists in cytoplasm as a non-toxic osmolyte and its concentration increases so as to maintain the osmotic balance of the cell when plants are stressed. At the same time, it acts as a low molecular weight chaperone to stabilize the structure of the protein and enzyme so that they can keep in functional conformation. Synthesis of glycinebetaine needs the catalysis of betaine aldehyde dehydrogenase (BADH) encoded by BADH gene that converts betaine aldehyde into glycinebetaine in some salt-tolerant plants.Rice is grown widely in the world with moderate sensitivity to salinity. The most effective approach to improve rice salt tolerance is to breed salt-tolerant varieties. In order to breed cultivars with salt tolerance, genetic analysis and relevant gene cloning for salt tolerance in rice should be studied. BADH gene family has been known to associate with stress tolerance in plants. In rice, there are two homologous genes, BADH1 and BADH2.We transformed BADH2-derived RNAi vector mediated by the EHA105 strain of Agrobacterium tumefaciens into several rice cultivars. PCR analysis demonstrated that the exogenous BADH2 gene fragment had been integrated into the genome of transformed rice plants. The results showed that two factors including sources of calli and genotype affected the efficiency of calli induction and transformation. For the same rice cultivar, the efficiencies of calli induction and transformation derived from young embryos were higher than that from mature embryos. Genotype was another factor affecting the formation of hygromycin-resistant calli and percentage of positive transformed plantlets. It was showed that both hygromycin and basta had good selective effects. Comparing calli selected by hygromycin with those by basta, the former was easier to regenerate and the latter appeared to grow stronger.Salt threatening experiment suggested that there's little difference between wild type and transformed plants in term of inhibition rate indicated by plant height and root length. Transgenic progenies were obtained by self-pollination in controlled conditions and were used for progeny analysis. Speed of germination of transgenic seeds were lower than that of wild type. The original metabolism may be disturbed by the exogenous BADH2 gene. Whether this phenomena was caused by the exogenous BADH2 gene needs further investigation.