Conservation of immunosuppression by Xanthomonadales commensals in Arabidopsis roots

植物的根是由一个系统发育结构的微生物群落定植的，称为根微生物群。我们表明，该群落的细菌成员属于根微生物群的不同分类群，其抑制根中免疫相关反应的能力不同。黄单胞菌目定义了开花植物根部微生物群的一个核心谱系，包括拟南芥。我们的初步结果表明，黄菌根共生物的免疫抑制能力可能是由一个保守的分子机制介导的。目前尚不清楚共生体是否仅通过空间和时间控制的防御反应操作在特定的根位中起作用。我们选择了共生Rhodanobacter R179，这是原生于拟南芥（a . thaliana）根部的，代表了Xanthomonadales的最深分支，并利用R179转座子插入突变体文库在植物中进行了突变体筛选。与野生型共体相比，鉴定出10个防御抑制系统（dss） R179插入突变体的免疫抑制活性受损。我们将研究在单一关联和社区背景下，免疫抑制对根定植时空控制的假设作用。dss突变体也将作为定义罗丹诺杆菌R179免疫抑制的分子机制的基础。我们将研究dss依赖性免疫抑制在系统发育不同的植物相关黄单胞菌根共生体中的保守性。最后，我们将阐明dss和t3ss依赖的免疫抑制机制的贡献，以及它们对黄单胞菌病原菌在叶片中定植的潜在相互依赖性。

Plant roots are colonized by a phylogenetically structured microbial community, called the root microbiota. We show that bacterial members of this community belonging to different taxa of the root microbiota differ in their ability to suppress immunity-associated responses in roots. The order Xanthomonadales defines a core lineage of the root microbiota of flowering plants, including Arabidopsis thaliana. Our preliminary results indicate that the ability of Xanthomonadales root commensals for immunosuppression is likely mediated by a conserved molecular mechanism. It remains unclear whether the commensals act only in specific root niches through a spatially and temporally controlled manipulation of defence responses. We selected the commensal Rhodanobacter R179, native to A. thaliana roots and representing the deepest branch of the order Xanthomonadales, and performed a mutant screen in planta using a library of R179 transposon insertion mutants. Ten defense suppression system (dss) R179 insertion mutants were identified that display impaired immunosuppressive activities compared with the wild-type commensal. We will investigate the presumed role of immunosuppression for spatio-temporal control of root colonization in mono-associations and community contexts. The dss mutants will also serve as basis to define the molecular mechanism(s) underlying Rhodanobacter R179 immunosuppression. We will examine the conservation of dss-dependent immunosuppression in phylogenetically diverse plantassociated Xanthomonadales commensals in roots. Finally, we will clarify the contribution of dss- and T3SS-dependent immunosuppression mechanisms and their potential mutual dependence for Xanthomonas pathogen colonisation in leaves.