苜蓿中华根瘤菌desA基因功能的鉴定

为研究苜蓿中华根瘤菌脂肪酸脱饱和酶desA基因在不饱和脂肪酸合成、共生结瘤固氮以及应对逆境胁迫中的功能,为高效利用苜蓿中华根瘤菌提供理论依据,本文通过异体遗传互补和脂肪酸组成薄层层析,分析SmdesA编码蛋白是否具有脱饱和酶的活性并参与不饱和脂肪酸的合成,构建SmdesA的缺失突变株和互补菌株,比较各菌株在不同逆境胁迫条件下的生长速率以及回接宿主植物后与紫花苜蓿共生结瘤的能力.结果表明SmdesA不能互补大肠杆菌CY57中EcfabA的突变,但具有将饱和脂肪酸脱饱和形成不饱和的棕榈油酸和十八碳烯酸的能力.另外,SmdesA缺失突变对苜蓿中华根瘤菌的脂肪酸组成影响不大,但会显著影响低温和高盐条件下菌株的生长速率以及与紫花苜蓿共生结瘤的能力.我们推测,SmdesA参与的脱饱和途径可能是苜蓿中华根瘤菌不饱和脂肪酸合成的补偿途径,其编码的蛋白DesA不是不饱和脂肪酸合成的关键酶,但在应对逆境胁迫和共生结瘤中具有重要的生物学功能.

Identification and Function Reasearch of desA of Sinorhizobium meliloti

Unsaturated fatty acids play important roles in Sinorhizobium meliloti adaptation to external environment stress and symbiotic nodulation. The symbiotic plasmid A of S. meliloti encodes a DesA homologue, which has 44% identity to Bacillus subtilis DesA. However, whether S. meliloti DesA is able to play functions in fatty acid synthesis was not determined. We report that though SmdesA gene could not restore the growth of E. coli fabA temperature sensitive mutant CY57 under non-permissive conditions, argentation thin layer chromatography assay show that CY57 carrying desA encoded plasmid could produce palmitoleic acid and octadecadienoic acid. This indicate that SmdesA encodes acyl-lipid desaturase. In addition, deletion of SmdesA gene have led to a little effects on the fatty acid composition of S. meliloti, but show a significant impact on growth rate in low temperature and high salt conditions, and the ability of alfalfa symbiotic nodulation. DesA is not the key enzyme of unsaturated fatty acid synthesis of S. meliloti, but it plays important biological roles in S. meliloti dealing with environment stress and nodular process.