HHMI, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Department of Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.
Proc Natl Acad Sci U S A. 2021 Apr 20;118(16). doi: 10.1073/pnas.2100678118.
Plants have an innate immune system to fight off potential invaders that is based on the perception of nonself or modified-self molecules. Microbe-associated molecular patterns (MAMPs) are evolutionarily conserved microbial molecules whose extracellular detection by specific cell surface receptors initiates an array of biochemical responses collectively known as MAMP-triggered immunity (MTI). Well-characterized MAMPs include chitin, peptidoglycan, and flg22, a 22-amino acid epitope found in the major building block of the bacterial flagellum, FliC. The importance of MAMP detection by the plant immune system is underscored by the large diversity of strategies used by pathogens to interfere with MTI and that failure to do so is often associated with loss of virulence. Yet, whether or how MTI functions beyond pathogenic interactions is not well understood. Here we demonstrate that a community of root commensal bacteria modulates a specific and evolutionarily conserved sector of the immune system. We identify a set of robust, taxonomically diverse MTI suppressor strains that are efficient root colonizers and, notably, can enhance the colonization capacity of other tested commensal bacteria. We highlight the importance of extracellular strategies for MTI suppression by showing that the type 2, not the type 3, secretion system is required for the immunomodulatory activity of one robust MTI suppressor. Our findings reveal that root colonization by commensals is controlled by MTI, which, in turn, can be selectively modulated by specific members of a representative bacterial root microbiota.
植物具有先天免疫系统，可以抵御潜在的入侵者，该系统基于对非自身或修饰自身分子的感知。微生物相关分子模式（MAMP）是进化上保守的微生物分子，其细胞外检测由特定的细胞表面受体启动，引发一系列生化反应，统称为 MAMP 触发免疫（MTI）。经过充分研究的 MAMP 包括几丁质、肽聚糖和 flg22，flg22 是细菌鞭毛主要构建块 FliC 中发现的 22 个氨基酸表位。植物免疫系统对 MAMP 检测的重要性突出表现在病原体用来干扰 MTI 的策略的多样性，而且未能做到这一点通常与毒力丧失有关。然而，MTI 在致病相互作用之外的功能如何还不是很清楚。在这里，我们证明了一群根共生细菌调节了免疫系统的一个特定且进化上保守的部分。我们确定了一组强大的、分类多样的 MTI 抑制菌株，它们是有效的根定殖者，值得注意的是，它们可以增强其他测试的共生细菌的定殖能力。我们通过显示 2 型而不是 3 型分泌系统是一种强大的 MTI 抑制因子免疫调节活性所必需的，强调了细胞外策略在 MTI 抑制中的重要性。我们的研究结果表明，共生体的根定植受 MTI 控制，而 MTI 又可以被代表细菌根微生物群的特定成员选择性调节。
