A transcriptome study of DSF-mediated quorum sensing in Xanthomonas axonopodis pv. citri. A transcriptome study of DSF-mediated quorum sensing in Xanthomonas axonopodis pv. citri

Quorum sensing (QS) in Xanthomonas axonopodis pv. citri, the causal agent of citrus canker, is mediated by a diffusible signal factor (DSF). QS is required for the full virulence of X. axonopodis pv. citri in planta. Mutations in rpfF, rpfC and rpfG, the core genes of QS, decreased the production of extracellular proteases and bacterial motility. Comparison of the transcriptomes of QS mutants with that of the wild type stain revealed that QS temporally regulates the expression of a large set of genes, including genes involved in chemotaxis and flagellar biosynthesis, genes related to metabolism, genes encoding virulence traits such as type II secretion system substates, type III secretion system and effectors. Cross talk between the QS regulon and the HrpG regulon has also been identified by 62 common genes shared by both regulons. The temporal regulation of the QS regulon and cross talk with the HrpG regulon suggest the important role of QS in citrus canker infection, including attachment, invasion and growth in host apoplast. Overall design: Three mutants and two time-points experiment. Four biological and dye-swap replicates of each strain per each time-point were used. In total, there were two datasets of the rpfF mutant: 1) rpfF mutant vs. wild type strain at 11 h, and 2) rpfF mutant vs. wild type strain at 25 h; two datasets of the rpfC mutant: 1) rpfC mutant vs. wild type strain at 11 h, and 2) rpfC mutant vs. wild type strain at 25 h; and two datasets of the rpfG mutant: 1) rpfG mutant vs. wild type strain at 11 h, and 2) rpfG mutant vs. wild type strain at 25 h.

柑橘溃疡病病原菌Xanthomonas axonopodis pv. citri中的群体感应（Quorum sensing, QS）由扩散信号因子（diffusible signal factor, DSF）介导。群体感应对于该病原菌在植物体内的完全致病力至关重要。群体感应的核心基因rpfF、rpfC与rpfG发生突变后，病原菌的胞外蛋白酶产量与细菌运动能力均会下降。对QS突变体与野生型菌株的转录组（transcriptome）比较分析显示，QS可时序调控大量基因的表达，包括趋化性与鞭毛生物合成相关基因、代谢相关基因、编码致病性状的基因（如II型分泌系统底物、III型分泌系统及其效应蛋白）。通过两组调节子（regulon）共有的62个共同基因，研究还发现QS调节子与HrpG调节子之间存在交叉串扰。QS调节子的时序调控特性及其与HrpG调节子的交叉串扰，提示群体感应在柑橘溃疡病侵染过程——包括宿主附着、入侵及在宿主质外体（apoplast）中的增殖——中发挥关键作用。实验设计概述：本实验设置3株突变体与2个采样时间节点。每个菌株在每个时间点均设置4次生物学重复与染料交换重复。总计包含6组数据集：1）11 h时rpfF突变体 vs 野生型菌株；2）25 h时rpfF突变体 vs 野生型菌株；3）11 h时rpfC突变体 vs 野生型菌株；4）25 h时rpfC突变体 vs 野生型菌株；5）11 h时rpfG突变体 vs 野生型菌株；6）25 h时rpfG突变体 vs 野生型菌株。