抗甲磺隆假单胞菌的分离及其乙酰乳酸合酶的大小亚基ilvIH基因的克隆和表达

乙酰乳酸合酶(也称乙酰羟酸合酶acetohydroxyacid synthase,AHAS)是植物、真菌和细菌细胞内支链氨基酸Val、Leu、Ile生物合成过程中关键酶,是乙酰乳酸合酶抑制剂类除草剂如磺酰脲类、咪唑啉酮类、嘧啶水杨酸和磺酰氨类的作用靶标.目的]获得抗甲磺隆的乙酰乳酸合酶基因,构建其表达载体,并分析基因中的位点突变与乙酰乳酸合酶对磺酰脲类除草剂抗性产生原因.方法]从长期使用甲磺隆的土壤中分离到l株抗甲磺隆的菌株Lm10,利用PCR技术从Lm10总DNA中克隆到乙酰乳酸合酶的大小亚基基因ilvIH,对ilvIH氨基酸序列进行比对分析.分别将ilvI和ilvH分别连接到表达载体pET29a( )多克隆位点,转化大肠杆菌(Escherichia coli)获得转化子BL21(pET-I)和BL21(pET-H),并诱导表达.结果]菌株Lm10鉴定为假单孢菌(Pseudomonas sp.),对甲磺隆的最高耐受浓度达到14000 μmol/L,且对各种乙酰乳酸合酶抑制剂类除草剂具有交叉抗性.Lm10与甲磺隆敏感菌株KT2440的小亚基氨基酸序列完全相同,而大亚基有6个氨基酸位点发生变异.转化子在IPTG诱导下,乙酰乳酸合酶的大小亚基的蛋白成功表达,粗酶液酶活试验结果表明Lm10的ilvI基因表达的乙酰乳酸合酶大亚基对甲磺隆有很强的抗性.结论]发现菌株Lm10的乙酰乳酸合酶大亚基对甲磺隆有很强的抗性,抗甲磺隆菌株Lm10与敏感菌株KT2440的ilvI有6个氨基酸位点差异,这些位点突变可能是乙酰乳酸合酶对甲磺隆抗性产生的原因.

Isolation of a metsulfuron-methyl-resistant bacteria and cloning and expres-sion of the acetohydroxyacid synthase genes ilvIH

Abstract: Acetohydroxyacid synthase (EC 4.1.3.18) is the enzyme that catalyses the first step in the synthesis of the branched-chain amino acids valine, leucine and isoleucine in plant, fungi and bacteria, and also is target of the sulfony-lurea, imidazolinone, triazolopyrimidine and other acetohydroxyacid synthase inhibitor herbicides. Objective] The pur-pose of this study is to get the resistant gene, prepare a functional bacteria with acetohydroxyacid synthase, and investi-gate the relationship between the mutation sites of the acetohydroxyacid synthase and the herbicides-resistant. Methods] A metsulfuron-methyl-resistant bacterium Lm10 was isolated from metsulfuron-methyl contaminated soil. Acetohy-droxyacid synthase genes ilvIH was amplified from the genome DNA of strains Lm10 by PCR. The ilvI and ilvH were cloned into the bacterial expression vector pET29a(+) respectively. Results] Strain Lm10 was identified preliminarily as Pseudomonas sp.. It can endure 14000 mmol/L metsulfuron-methyl and showed cross resistance to diffenent acetohy-droxyacid synthase inhibitor herbicids, such as chlorsulfuron, imazethapyr, flumetsulam and penoxsulam. The alignment result of the ilvIH amino acid sequence showed that ilvI of strains Lm10 differed from that of strain KT2440 by 6 sites, While the ilvH of the two strains were the same. The gene ilvI and ilvH were functional expressed in the Escherichia coli strain BL21(DE3) respectively. The expressed production pET-I displayed acetohydroxyacid synthase activity and showed re-sistance to high concentration of metsulfuron-methyl. Conclusion] The ilvI displayed acetohydroxyacid synthase activity. The 6 different sites in ilvI of strains Lm10 probably led to herbicids resistance.