Light cues induce transcriptional reprogramming and protective anticipation of environmental water loss in Pseudomonas syringae

The ecological significance of light perception in non-phototrophic bacteria remains largely elusive. In terrestrial environments, diurnal oscillations in light are often temporally coupled to other environmental changes, including increased temperature and evaporation. Here we report that light functions as an anticipatory cue that triggers protective adaptations to tolerate a future rapid loss of environmental water in leaf-associated Pseudomonas syringae pv. syringae (Pss) and other terrestrial pseudomonads. Global transcriptome analyses in Pss showed that light control occurs almost entirely through a bacteriophytochrome photoreceptor that senses red, far-red and blue wavelengths and influences 30% of the Pss genome. Bacteriophytochrome-mediated light control disproportionally upregulates water-stress adaptation functions and confers enhanced fitness when cells encounter light prior to water limitation. These data demonstrate that non-phototrophic bacteria can use light as a cue to mount an adaptive anticipatory response against a physiologically unrelated but ecologically coupled stress. Overall design: Comparative gene expression profiling analysis of RNA-seq data for Pseudomonas syringae pv. syringae strain B278a and isogenic mutants following brief exposure to different light wavelengths

非光养型细菌（non-phototrophic bacteria）的光感知行为，其生态学意义迄今尚未得到充分阐释。在陆地生境中，光照的昼夜节律波动往往与其他环境变化在时间上同步，例如温度升高与蒸发加剧。本研究表明，光照可作为一种预见性信号，在定殖于植物叶片的丁香假单胞菌丁香致病变种（Pseudomonas syringae pv. syringae，简称Pss）及其他陆地假单胞菌属物种中，触发保护性适应机制，以应对未来可能快速出现的环境水分流失。对Pss的全局转录组分析结果显示，光照调控几乎完全通过一种可感知红光、远红光与蓝光波长的细菌光敏色素（bacteriophytochrome）光受体介导，该受体可调控Pss基因组中30%的基因表达。由细菌光敏色素介导的光照调控，会不成比例地上调水分胁迫适应相关功能；当菌体在遭遇水分限制前先接触光照时，可显著提升其生存适合度。上述研究数据表明，非光养型细菌可将光照作为信号，针对生理上无关但生态上偶联的胁迫发起适应性预见性应答。实验设计：对丁香假单胞菌丁香致病变种菌株B278a及其同基因系突变体，在短暂暴露于不同波长光照后获取的RNA测序数据，开展比较基因表达谱分析。