Studies On Drought-resistance Of Transgenic Tobacco Expressing Betaine Synthetase Gene And Agrobacterium-tumefacience Mediated Gene Transformation Of Aspen (Populus Davidiana Dove)

Betaine is one of the best osmopretectant studied, and its synthetic pathway is simple. In higher plants, betaine is synthesized in two-steps: the fist one is catalyzed by choline monooxygenase (CMO) and the second one is catalyzed by betaine aldehyde dehydrogenase(BADH). Several studies on drought-resistance and salt-resistance improved transgenic tobacco expressing CMO and BADH gene were reported, but there is no systematic physiological study on their drought-resistance characters. Populus is an important fast-grow economical forest tree species to which genetic manipulation system is well established and transgenic Populus with improved insect-resistance, herbicide-resistance and other characters were obtained, but no report is related to CMO and BADH transformation. We reported here systematic physiological studies on drought-resistant characters of transgenic tobacco expressing betaine synthetase genes. At the same time, we established Agrobacterium-tumefacience mediated gene transformation system of Aspen (Populus davidiana Dove) and obtained PCR and Southern dot positive plants transformed with CMO and BADH gene.In stress conditions, superoxide dismutase(SOD) activity, peroxidase (POD)activity and water potential of transgenic plants were generally higher than that of the control, while leaf relative leakage electrolytes and lose rate of transgenic plants were generally lower. These results indicated that betaine synthetase gene transformation contributed to improved drought resistance of tobacco.Populus is an importantly economical forest tree species, and have small genomes and are easy for tissue culture that make them well study as model plants of tree genetic engineering. At the same time, the traditional tree breeding limiting the improving the resistance of the populus. Engineering has quickly been developed and widely applied to improved the quality of populus. In this paper, the rapid and stable regeneration system was established that is suit to use for gene-transformation mediate by Agrobacterium tumefaciens.Leaf explants were infected with A.t. strain LBA4404 carrying antibiotic-resistance gene and betaine synthetase gene. 48 Km resistant shoots transformed with CMO gene and 6 hygromycin resistant shoots transformed with BADH gene were obtained. PCR and Southern dot analysis of some resistant shoots preliminarily indicated foreign genes had integrated into the genome of Aspen.Studies on factors influencing Aspen leaf disc transformation implied that 500mg/L Cef., 20mg/LKm or 3-5mg/L Hyg, 2-3 days preculture, about OD6oo 0.5 of Agrobacterium culture, 5min infection and 2~3days co-culture were optimized conditions.