A Sinorhizobium meliloti lipopolysaccharide mutant altered in cell surface sulfation
A Sinorhizobium meliloti lipopolysaccharide mutant altered in cell surface sulfation
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DOI：
10.1128/jb.184.23.6681-6689.2002
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发表时间：
2002-12-01
影响因子：
3.2
通讯作者：
Long, SR
中科院分区：
文献类型：
--
作者：
Keating, DH;Willits, MG;Long, SR
根瘤菌 - 豆科植物共生涉及一种新型植物器官——根瘤的形成，在根瘤中，胞内细菌还原分子态二氮以换取植物的光合产物。根瘤发育需要一种被称为结瘤因子的细菌信号，在苜蓿中华根瘤菌中，结瘤因子是一种β-(1,4) - 连接的N - 乙酰葡糖胺四聚体，在非还原端含有N - 酰基和O - 乙酰基修饰，在还原端含有关键的6 - O - 硫酸盐。这种硫酸盐修饰需要三种基因产物的作用：催化磺酰基转移的nodH，以及产生活化形式硫酸盐（5′ - 磷酰硫酸腺苷）的nodPQ。先前有报道称，苜蓿中华根瘤菌的细胞表面多糖也在依赖于nodPQ的反应中被硫酸盐共价修饰。我们进一步对这种独特的细菌碳水化合物修饰形式进行了表征。我们的研究确定，在最初对细胞表面硫酸化研究中使用的一个nodPQ突变株携带有第二个不连锁的突变。我们克隆了受此突变影响的基因（称为lps - 212），发现它是lpsL的一个等位基因，lpsL是一个先前被预测编码UDP - 葡萄糖醛酸差向异构酶的基因。我们证明了IpsL编码一种UDP - 葡萄糖醛酸差向异构酶活性，该活性在lps - 212突变体中降低。Ips - 212突变导致脂多糖结构改变，其在体外和体内的硫酸盐修饰减少。最后，我们确定lps - 212突变导致诱导植物根瘤形成的能力降低，并且感染线结构发生改变，过早终止。
The Rhizobium-legume symbiosis involves the formation of a novel plant organ, the nodule, in which intracellular bacteria reduce molecular dinitrogen in exchange for plant photosynthates. Nodule development requires a bacterial signal referred to as Nod factor, which in Sinorhizobiurn meliloti is a beta-(1,4)-linked tetramer of N-acetylglucosamine containing N-acyl and O-acetyl modifications at the nonreducing end and a critical 6-O-sulfate at the reducing end. This sulfate modification requires the action of three gene products: nodH, which catalyzes the sulfonyll transfer, and nodPQ, which produce the activated form of sulfate, Y-phosphoadenosine-5'-phosphosulfate. It was previously reported that S. meliloti cell surface polysaccharides are also covalently modified by sulfate in a reaction dependent on NodPQ. We have further characterized this unique form of bacterial carbohydrate modification. Our studies have determined that one of the nodPQ mutant strains used in the initial study of sulfation of cell surface harbored a second unlinked mutation. We cloned the gene affected by this mutation (referred to as lps-212) and found it to be an allele of lpsL, a gene previously predicted to encode a UDP-glucuronic acid epimerase. We demonstrated that IpsL encoded a UDP-glueuronic acid epimerase activity that was reduced in the lps-212 mutant. The Ips-212 mutation resulted in an altered lipopolysaccharide structure that was reduced in sulfate modification in vitro and in vivo. Finally, we determined that the lps-212 mutation resulted in a reduced ability to elicit the formation of plant nodules and by altered infection thread structures that aborted prematurely.