Laboratoire de Recherche en Sciences Végétales, Université de Toulouse, CNRS, UPS, 24 chemin de Borde Rouge, Auzeville, BP42617, 31326, Castanet Tolosan, France.
Laboratory of Plant-Microbe Interactions (LIPM), Université de Toulouse, INRA, CNRS, 31326, Castanet-Tolosan, France.
New Phytol. 2019 Jan;221(2):743-749. doi: 10.1111/nph.15574. Epub 2018 Nov 26.
Molecular signals released by microbes at the surface of plant roots and leaves largely determine host responses, notably by triggering either immunity or symbiosis. How these signalling pathways cross-talk upon coincident perception of pathogens and symbionts is poorly described in plants forming symbiosis. Nitrogen fixing symbiotic Rhizobia spp. and arbuscular mycorrhizal fungi produce lipo-chitooligosaccharides (LCOs) to initiate host symbiotic programmes. In Medicago truncatula roots, the perception of LCOs leads to reduced efflux of reactive oxygen species (ROS). By contrast, pathogen perception generally triggers a strong ROS burst and activates defence gene expression. Here we show that incubation of M. truncatula seedlings with culture filtrate (CF) of the legume pathogen Aphanomyces euteiches alone or simultaneously with Sinorhizobium meliloti LCOs, resulted in a strong ROS release. However, this response was completely inhibited if CF was added after pre-incubation of seedlings with LCOs. By contrast, expression of immunity-associated genes in response to CF and disease resistance to A. euteiches remained unaffected by LCO treatment of M. truncatula roots. Our findings suggest that symbiotic plants evolved ROS inhibition response to LCOs to facilitate early steps of symbiosis whilst maintaining a parallel defence mechanisms toward pathogens.
植物根和叶表面微生物释放的分子信号在很大程度上决定了宿主的反应，特别是通过触发免疫或共生。在形成共生关系的植物中，这些信号通路在同时感知病原体和共生体时如何相互作用的描述甚少。固氮共生根瘤菌和丛枝菌根真菌产生脂壳寡糖（LCOs）来启动宿主共生程序。在蒺藜苜蓿根中，LCOs 的感知导致活性氧（ROS）的外排减少。相比之下，病原体的感知通常会引发强烈的 ROS 爆发并激活防御基因表达。在这里，我们表明，单独或同时用豆科植物病原体 Aphanomyces euteiches 的培养滤液（CF）和 Sinorhizobium meliloti LCOs 孵育蒺藜苜蓿幼苗会导致强烈的 ROS 释放。然而，如果在 LCO 预孵育后添加 CF，则该反应会完全受到抑制。相比之下，LCO 处理对蒺藜苜蓿根中 CF 和对 A. euteiches 的疾病抗性的免疫相关基因表达没有影响。我们的研究结果表明，共生植物进化出了 ROS 抑制对 LCOs 的反应，以促进共生的早期步骤，同时对病原体保持平行的防御机制。
