野油菜黄单胞菌中3-羟基脂酰ACP脱水酶FabZ的生理功能

Physiological functions of 3-hydroxyacyl ACP dehydratase FabZ in Xanthomonas campestris pv. campestris

摘要:

【背景】野油菜黄单胞菌（Xanthomonas campestris pv.campestris，Xcc）引起十字花科植物黑腐病，在全球范围内造成经济损失，亟须深入研究其致病机理，开发新的黑腐病防控措施。细菌脂肪酸合成系统不仅为细胞膜合成提供原料，其中间代谢产物还是许多生物活性分子合成的底物，具有重要的生理功能，也是抗菌药物筛选的重要靶标。【目的】研究Xcc fabZ对扩散信号分子（diffusible signal factor，DSF）类信号产量、致病力、胞外酶、胞外多糖和运动性等方面的影响。【方法】利用报告菌株检测法分析了不同替换突变株的DSF类群体感应信号产量。利用同源重组原理，在DSF类信号高产菌株中获得替换突变株，利用高效液相色谱（high performance liquid chromatography，HPLC）法测定DSF类信号产量。利用剪叶法检测替换突变株对寄主植物甘蓝的致病力，并分析了不同菌株的胞外多糖、胞外酶和运动性差异。【结果】报告菌株检测法和HPLC法都证明大肠杆菌fabZ替换突变株（Xcc ΔfabZ/pSRK-Ec fabZ）中DSF类信号产量显著下降。而该突变株对寄主植物的致病性也下降，在白菜提取物中生长也变慢，胞外酶产量下降，运动性也变弱。而Xcc fabZ替换突变株的DSF类信号产量恢复到野生菌水平，且过量产生胞外多糖使得致病性增强，胞外酶、运动性也都有所恢复。【结论】Xcc中3-羟基脂酰ACP脱水酶（FabZ）与其致病性相关，不仅影响DSF类信号产量，还在胞外酶、运动性等方面发挥作用。

关键词:野油菜黄单胞菌;3-羟基脂酰ACP脱水酶;DSF类信号;致病性

Abstract:

[Background] Xanthomonas campestris pv. campestris (Xcc) is the pathogen of black rot in cruciferous plants, causing immense economic losses worldwide. Therefore, it is urgent to study the pathogenic mechanism of this pathogen and develop novel methods to control this disease. The bacterial fatty acid synthesis system provides not only substrates for cell membrane synthesis but also the intermediates to be used as precursors for the synthesis of bioactive molecules. With important functions, the fatty acid synthesis system is a promising target for the screening of antibacterial agents. [Objective] To investigate the effects of Xcc fabZ on the diffusible signal factor (DSF) family signals production, pathogenicity, extracellular enzymes, extracellular polysaccharides, and motility of Xcc. [Methods] The yields of DSF family signals produced by different strains were estimated by the bioassay method with the DSF reporter strain. The replacement mutants were established from the DSF family signals high yield strain based on homologous recombination. Then, the yields of DSF family signals were determined by high performance liquid chromatography (HPLC). The pathogenicity of different strains to the host plant Brassica oleracea L. was examined by the leaf-clipping method, and the production of exopolysaccharides (EPS), extracellular enzymes, and motility were compared among different strains. [Results] The DSF family signals produced by the Escherichia coli fabZ replacement mutant (Xcc ΔfabZ/pSRK-EcfabZ) decreased sharply. Moreover, the mutant presented attenuated pathogenicity to the host plant, slow growth in the plant extract, reduced extracellular enzyme production, and weakened motility. The production of DSF family signals by the Xcc fabZ replacement mutant was restored to the level of the wild-type strain, and excessive production of EPS enhanced the pathogenicity and restored the extracellular enzymes and motility. [Conclusion] FabZ affects the production of DSF family signals and extracellular enzymes, pathogenicity, and motility of Xcc.

Key words:Xanthomonas campestris pv. campestris;3-hydroxyacyl ACP dehydratase;DSF family signals;pathogenicity