beta-glucan synthesis in Bradyrhizobium japonicum: Characterization of a new locus (ndvC) influencing beta-(1->6) linkages
beta-glucan synthesis in Bradyrhizobium japonicum: Characterization of a new locus (ndvC) influencing beta-(1->6) linkages
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DOI：
10.1128/jb.178.15.4635-4642.1996
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发表时间：
1996-08-01
影响因子：
3.2
通讯作者：
Keister, DL
中科院分区：
文献类型：
--
作者：
Bhagwat, AA;Gross, KC;Keister, DL
慢生根瘤菌在低渗环境中生长过程中会合成周质环状β-(1-gt；3)，β-(1-gt；6)-D-葡聚糖，越来越多的证据表明这些分子在植物-微生物相互作用过程中除了渗透调节外还可能具有特定的功能。NdvB上游DNA区域的定点Tn5突变导致了一个新基因(NdvC)的鉴定，该基因与β-(1->；3)、β-(1-->；6)-葡聚糖合成和根瘤发育有关。预测的翻译产物是一个含有多个跨膜结构域的多肽(约62 kDa)。它含有一个在许多细菌酶中发现的保守的核苷糖结合基序的序列特征，并与来自白色念珠菌的β-葡聚糖基转移酶有51%的相似性。B.Japan onicum在ndvC中携带Tn5插入导致合成几乎完全由β-(1->；3)-糖基键组成的改变的环状β-葡聚糖。与ndvB突变株相比，突变株对低渗生长条件的敏感性较低，但与大豆(Glycinmax)的共生作用严重受损。结瘤延迟了8-10天，形成了许多明显缺乏活细菌的小结节状结构。这一发现表明，β-葡聚糖分子的结构对于成功的共生相互作用很重要，除了在低渗适应中的作用外，β-葡聚糖可能还有特定的功能。
Bradyrhizobium japonicum synthesizes periplasmic cyclic beta-(1-->3),beta-(1-->6)-D-glucans during growth in hypoosmotic environments, and evidence is growing that these molecules may have a specific function during plant-microbe interactions in addition to osmoregulation. Site-directed Tn5 mutagenesis of the DNA region upstream of ndvB resulted in identification of a new gene (ndvC) involved in beta-(1-->3),beta-(1-->6)-glucan synthesis and in nodule development. The predicted translation product was a polypeptide (ca. 62 kDa) with several transmembrane domains. It contained a sequence characteristic of a conserved nucleoside-sugar-binding motif found in many bacterial enzymes and had 51% similarity with a beta-glucanosyltransferase from Candida albicans. B. japonicum carrying a Tn5 insertion in ndvC resulted in synthesis of altered cyclic beta-glucans composed almost entirely of beta-(1-->3)-glycosyl linkages. The mutant strain was only slightly sensitive to hypoosmotic growth conditions compared with the ndvB mutant, but it was severely impaired in symbiotic interactions with soybean (Glycine max). Nodulation was delayed by 8 to 10 days, and many small nodule-like structures apparently devoid of viable bacteria were formed. This finding suggests that the structure of the beta-glucan molecule is important for a successful symbiotic interaction, and beta-glucans may have a specific function in addition to their role in hypoosmotic adaptation.