Deciphering the dual effect of lipopolysaccharides from plant pathogenic <i>Pectobacterium</i>

Lipopolysaccharides (LPS) are a component of the outer cell surface of almost all Gram-negative bacteria and play an essential role for bacterial growth and survival. Lipopolysaccharides represent typical microbe-associated molecular pattern (MAMP) molecules and have been reported to induce defense-related responses, including the expression of defense genes and the suppression of the hypersensitive response in plants. However, depending on their origin and the challenged plant, LPS were shown to have complex and different roles. In this study we showed that LPS from plant pathogens Pectobacterium atrosepticum and Pectobacterium carotovorum subsp. carotovorum induce common and different responses in A. thaliana cells when compared to those induced by LPS from non-phytopathogens Escherichia coli and Pseudomonas aeruginosa. Among common responses to both types of LPS are the transcription of defense genes and their ability to limit of cell death induced by Pectobacterium carotovorum subsp carotovorum. However, the differential kinetics and amplitude in reactive oxygen species (ROS) generation seemed to regulate defense gene transcription and be determinant to induce programmed cell death in response to LPS from the plant pathogenic Pectobacterium. These data suggest that different signaling pathways could be activated by LPS in A. thaliana cells.脂多糖（Lipopolysaccharides, LPS）是几乎所有革兰氏阴性菌细胞外表面的组成成分，对细菌的生长与存活至关重要。脂多糖属于典型的微生物相关分子模式（microbe-associated molecular pattern, MAMP），据报道可诱导植物产生防御相关应答，包括防御基因的表达以及对植物过敏反应的抑制。然而，研究表明脂多糖的功能会因来源及所侵染的植物而异，呈现出复杂多样的作用模式。本研究发现，相较于非植物病原菌大肠杆菌（Escherichia coli）与铜绿假单胞菌（Pseudomonas aeruginosa）来源的脂多糖所诱导的应答，植物病原菌黑腐果胶杆菌（Pectobacterium atrosepticum）及胡萝卜软腐果胶杆菌胡萝卜亚种（Pectobacterium carotovorum subsp. carotovorum）来源的脂多糖可在拟南芥（A. thaliana）细胞中诱导出共通与差异化的应答。两类脂多糖的共通应答包括防御基因的转录，以及二者均能抑制胡萝卜软腐果胶杆菌胡萝卜亚种诱导的细胞死亡。然而，活性氧（reactive oxygen species, ROS）生成的动力学差异与幅度差异，似乎可调控防御基因的转录，并成为决定植物针对植物病原果胶杆菌来源脂多糖产生程序性细胞死亡的关键因素。上述数据表明，脂多糖可在拟南芥细胞中激活不同的信号通路。