Glucomannan-Mediated Attachment of Rhizobium leguminosarum to Pea Root Hairs Is Required for Competitive Nodule Infection
Glucomannan-Mediated Attachment of Rhizobium leguminosarum to Pea Root Hairs Is Required for Competitive Nodule Infection
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DOI：
10.1128/jb.01694-07
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发表时间：
2008-04
影响因子：
3.2
通讯作者：
A. Williams;A. Wilkinson;M. Krehenbrink;D. Russo;Á. Zorreguieta;J. Downie
中科院分区：
文献类型：
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作者：
A. Williams;A. Wilkinson;M. Krehenbrink;D. Russo;Á. Zorreguieta;J. Downie
摘要豌豆根瘤菌生物变种的基因组中含有几个预测决定表面多糖的基因。预测影响多糖合成的初始步骤的突变体进行了鉴定和表征。除了已知的纤维素（cel）和酸性胞外多糖（EPS）（pss）基因，我们突变了其他三个位点;这些位点之一（gmsA）决定葡甘露聚糖合成和一个（gelA）决定凝胶形成多糖，但其他位点（exoY样基因）的作用没有确定。突变体进行了测试的附件和生物膜形成在体外和根毛;突变体缺乏的EPS是有缺陷的这两个特点，但突变的gelA或exoY样基因没有影响任何类型的附件。纤维素（celA）突变体附着并在体外形成正常的生物膜，但它没有在根毛上形成生物膜，尽管附着确实发生了。纤维素依赖的生物膜上的根毛似乎不是至关重要的，因为celA突变体竞争与野生型的结节感染。葡甘露聚糖（gmsA）突变体在体外附着并形成正常的生物膜，但在根毛上的附着和生物膜形成缺陷。虽然该突变体在豌豆上形成结节，但在混合接种中被野生型非常强烈地击败，表明葡甘露聚糖对竞争性生长至关重要。gmsA周围的多糖合成基因在其他根瘤菌和农杆菌中高度保守，但在密切相关的细菌（如布鲁氏菌）中缺失。这表明这些基因可能在细菌-植物相互作用中发挥广泛作用。
ABSTRACT The Rhizobium leguminosarum biovar viciae genome contains several genes predicted to determine surface polysaccharides. Mutants predicted to affect the initial steps of polysaccharide synthesis were identified and characterized. In addition to the known cellulose (cel) and acidic exopolysaccharide (EPS) (pss) genes, we mutated three other loci; one of these loci (gmsA) determines glucomannan synthesis and one (gelA) determines a gel-forming polysaccharide, but the role of the other locus (an exoY-like gene) was not identified. Mutants were tested for attachment and biofilm formation in vitro and on root hairs; the mutant lacking the EPS was defective for both of these characteristics, but mutation of gelA or the exoY-like gene had no effect on either type of attachment. The cellulose (celA) mutant attached and formed normal biofilms in vitro, but it did not form a biofilm on root hairs, although attachment did occur. The cellulose-dependent biofilm on root hairs appears not to be critical for nodulation, because the celA mutant competed with the wild-type for nodule infection. The glucomannan (gmsA) mutant attached and formed normal biofilms in vitro, but it was defective for attachment and biofilm formation on root hairs. Although this mutant formed nodules on peas, it was very strongly outcompeted by the wild type in mixed inoculations, showing that glucomannan is critical for competitive nodulation. The polysaccharide synthesis genes around gmsA are highly conserved among other rhizobia and agrobacteria but are absent from closely related bacteria (such as Brucella spp.) that are not normally plant associated, suggesting that these genes may play a wide role in bacterium-plant interactions.