Despite its importance for membrane stability and pathogenicity of mammalian pathogens, functions of the O‐polysaccharide (OPS) of lipopolysaccharide (LPS) remain unclear in plant‐associated bacteria. Genetic information about OPS biosynthesis in these bacteria is largely missing. Genome analysis of various plant‐associated Pseudomonas strains revealed that one of the two known OPS biosynthesis clusters from Pseudomonas aeruginosa PAO1, the common polysaccharide antigen (CPA) gene cluster, is only conserved in some strains of the Pseudomonas fluorescens group. For the O‐specific antigen (OSA) biosynthesis cluster, the putative genomic position could be identified, but orthologues of most functional important OSA biosynthesis enzymes could not be detected. Nevertheless, orthologues of the glycosyltransferase WbpL, required for initiation of CPA and OSA synthesis in P. aeruginosa PAO1, could be identified in the analysed Pseudomonas genomes. Knockout mutations of wbpL orthologues in Pseudomonas syringae pv. tomato DC3000 (Pst) and Pseudomonas cichorii ATCC10857/DSM50259 (Pci) resulted in strains lacking the OPS. Infection experiments of Arabidopsis thaliana plants revealed a reduced entry into the leaf apoplast after spray inoculation and a reduced apoplastic amplification of Pst ∆wbpL. Stab and spray inoculation of lettuce (Lactuca sativa) leaves with Pci ∆wbpL causes reduced infection symptoms compared to the wild‐type strain. Furthermore, swarming motility was reduced in ∆wbpL mutants of Pst and Pci. This might be a possible reason for reduced bacterial titres after surface inoculation and reduced bacterial amplification in the plant. Our results imply that the presence of lipopolysaccharide OPS is required for efficient host colonization and full virulence of plant‐pathogenic Pseudomonas bacteria.

中文翻译：

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wbpL的损失破坏了O-多糖的合成并损害了植物相关的假单胞菌菌株的毒力。

尽管它对哺乳动物病原体的膜稳定性和致病性具有重要意义，但在植物相关细菌中脂多糖（LPS）的O-多糖（OPS）的功能仍不清楚。这些细菌中有关OPS生物合成的遗传信息已大大丢失。对各种与植物相关的假单胞菌菌株的基因组分析表明，来自铜绿假单胞菌PAO1的两个已知OPS生物合成簇之一是常见的多糖抗原（CPA）基因簇，仅在荧光假单胞菌组的某些菌株中保守。对于O特异性抗原（OSA）生物合成簇，可以确定假定的基因组位置，但无法检测到大多数功能重要的OSA生物合成酶的直向同源物。然而，可以在分析的假单胞菌基因组中鉴定出启动铜绿假单胞菌PAO1中的CPA和OSA合成所需的糖基转移酶WbpL的直向同源物。丁香假单胞菌pv中wbpL直向同源物的敲除突变。番茄DC3000（Pst）和菊苣假单胞菌ATCC10857 / DSM50259（Pci）导致菌株缺乏OPS。拟南芥的感染实验喷雾接种后，植物减少了进入叶片质外体的进入，减少了Pst ∆ wbpL的质外体扩增。与野生型菌株相比，用Pci ∆ wbpL刺刺和喷雾接种莴苣（莴苣）叶片可减少感染症状。此外，Pst和Pci的∆ wbpL突变体的群体运动减少。这可能是表面接种后细菌滴度降低和植物中细菌扩增降低的可能原因。我们的结果表明，脂多糖OPS的存在对于有效的宿主定植和植物致病性的完全毒力是必需的假单胞菌细菌。