背景回顾：Plants grown in natural soil are colonized by phylogenetically structured communities of microbes known as the microbiota. Individual microbes can activate microbe-associated molecular pattern (MAMP)-triggered immunity (MTI), which limits pathogen proliferation but curtails plant growth, a phenomenon known as the growth–defence trade-off. 

主要研究：Here, we report that, in monoassociations, 41% (62 out of 151) of taxonomically diverse root bacterial commensals suppress Arabidopsis thaliana root growth inhibition (RGI) triggered by immune-stimulating MAMPs or damage-associated molecular patterns. 

结果1：Amplicon sequencing of bacterial 16S rRNA genes reveals that immune activation alters the profile of synthetic communities (SynComs) comprising RGI-non-suppressive strains, whereas the presence of RGI-suppressive strains attenuates this effect. 

结果2：Root colonization by SynComs with different complexities and RGI-suppressive activities alters the expression of 174 core host genes, with functions related to root development and nutrient transport. 

结果3：Furthermore, RGI-suppressive SynComs specifically downregulate a subset of immune-related genes. Precolonization of plants with RGI-suppressive SynComs, or mutation of one commensal-downregulated transcription factor, MYB15, renders the plants more susceptible to opportunistic Pseudomonas pathogens. 

结论：Our results suggest that RGI-non-suppressive and RGI-suppressive root commensals modulate host susceptibility to pathogens by either eliciting or dampening MTI responses, respectively. This interplay buffers the plant immune system against pathogen perturbation and defence-associated growth inhibition, ultimately leading to commensal–host homeostasis.

 摘 要 

生长在自然土壤中的植物通常会具有系统发育结构的微生物群落所定殖，即所谓的微生物群（microbiota）。单个的微生物会激活微生物相关分子模式（MAMP）诱发的免疫（MTI），这虽然限制了病原体的增殖，但也抑制了植物的生长，这种现象被称为生长与防御之间的平衡。本文中，作者发现在151个不同种类的根细菌共生体中，62个（约占41%）的共生体会抑制由能够刺激免疫的MAMPs或者损伤相关的分子模式所诱发的拟南芥根生长抑制（RGI）。对细菌16S rRNA的扩增测序显示，免疫激活会改变由RGI非抑制菌株组成的合成菌落谱，而RGI抑制菌株的存在则会减弱这种效应。具有不同复杂度和RGI抑制活性的合成菌落对根系的定殖，改变了174个核心寄主基因的表达，这些基因的功能主要与根系发育和养分运输有关。此外，RGI抑制型的合成菌落会特异性下调一类免疫相关的基因。通过对植物预定殖RGI抑制性合成菌落，或者突变一个共生下调的转录因子MYB15，能够使得植物对假单胞菌病原体更加敏感。本文的研究表明，非RGI抑制性和RGI抑制性的根共生菌，会分别通过引起和减弱MTI响应，从而改变寄主植物对病原菌的易感性。这种相互作用缓冲了植物免疫系统对病原体的干扰和防御相关的生长抑制，最终达到共生菌和宿主之间的稳态。