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ABC-转运系统将同质O-抗原多糖链从细胞质内膜转运到细胞周质空间合成脂多糖(LPS)。通过功能互补和亚克隆序列分析在X. oryzae pv. oryzicola的基因组文库中发现了一个Wzt基因, 该基因编码产物是运输O-抗原的ABC-转运系统的疏水组成部分,为ATP-结合蛋白。为区别基因来源将该基因命名为Wzt_(Xooc). Wzt_(Xooc)编码一个35.9 ku的蛋白质。通过分析发现,Wzt_(Xooc)与数据库中的其他细菌包括水稻白叶枯病菌的ABC-转运系统的ATP结合蛋白质不同。在Wzt_(Xooc)序列中仅发现ATP-结合蛋白中4个保守基序的3个,没有发现ATP-结合位点Walker A(ATP/GTP binding site motif A)。通过基因插入突变得到Wzt_(Xooc)基因突变体Mwzt。LPS分析表明:由于该基因突变使O- 抗原链不能转运通过细胞质膜,不能形成完整的LPS分子,突变体菌落表面丧失了产生大量胞外多糖的能力;突变细菌不产生鞭毛,丧失了游动性和生物膜形成的能力。重要的是突变体在水稻上的繁殖能力和致病性明显下降,证明Wzt_(Xooc)基因与LPS合成及致病性有关。
The ABC-transport system transports homogenous O-antigen polysaccharide chains from the cytoplasmic membrane to the periplasmic space to synthesize lipopolysaccharide (LPS). A Wzt gene was found in the genomic library of X. oryzae pv. Oryzicola by functional complementation and subclone sequence analysis. The gene encoding the product is the hydrophobic component of the ABC-transport system that carries the O-antigen and is an ATP-binding protein. The gene was named Wzt_ (Xooc) for the purpose of differentiating the gene. Wzt_ (Xooc) encodes a 35.9 ku protein. The analysis found that Wzt_ (Xooc) is different from the ATP-binding proteins of other bacteria in the database, including the ABC-transport system of X. oryzae. Only three of the four conserved motifs in the ATP-binding protein were found in the Wzt_ (Xooc) sequence and no ATP-binding site Walker A (ATP / GTP binding site motif A) was found. The Wzt Xooc gene mutant Mwzt was obtained by gene mutation. LPS analysis showed that the LPS gene could not form intact LPS molecules due to the inability of the O-antigen chain to transport through the plasma membrane due to the gene mutation, and the mutant colonies lost the ability to produce large amounts of exopolysaccharides on the surface of the colonies; the mutant bacteria did not produce flagella and lost their motility Sexual and biofilm formation ability. Importantly, the reproductive capacity and pathogenicity of the mutant in rice decreased significantly, demonstrating that the Wzt_ (Xooc) gene is involved in the synthesis and pathogenicity of LPS.