Specific Root Exudate Compounds Sensed by Dedicated Chemoreceptors Shape Azospirillum brasilense Chemotaxis in the Rhizosphere
Specific Root Exudate Compounds Sensed by Dedicated Chemoreceptors Shape Azospirillum brasilense Chemotaxis in the Rhizosphere
复制标题
由特异化学受体感受到的特定根分泌物化合物形成巴西固氮螺菌根际趋化性
DOI：
10.1128/aem.01026-20
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发表时间：
2020-05
影响因子：
4.4
通讯作者：
Lindsey O’Neal;Lam Vo;G. Alexandre
中科院分区：
文献类型：
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作者：
Lindsey O’Neal;Lam Vo;G. Alexandre
植物根系分泌物在塑造根际微生物群落中发挥着关键作用，而运动细菌对这些梯度做出反应的能力介导了根表面的竞争性定植。根系分泌物是复杂的化学混合物，在空间和时间上都是动态的。因此，确定介导土壤细菌招募到根部特定区域的确切化学物质具有挑战性。在这里，我们将细菌趋化反应和化学感受器感知的模式与根系分泌物梯度中发现的化学物质联系起来，并确定了在不同植物和根部区域中形成根表面定植的关键化学信号。摘要 植物根通过分泌招募不同细菌的化合物来塑造根际群落。能动的α-变形菌巴西固氮螺菌在各种植物根部的定植导致植物生长、根体积和作物产量增加。这种细菌和其他能动的土壤细菌的趋化性对于根表面的竞争性定殖至关重要。趋化性在根表面定植中的作用先前已通过对接种后几小时至几天检测到的细菌定植水平进行终点分析来确定。最近，微流体装置已被用于研究植物-微生物相互作用，但这些装置的尺寸有限。在这里，我们使用了一种新型滑入室，可以使用农业相关的幼苗实时监测植物与微生物的相互作用，以表征巴西曲霉与普通小麦（小麦）和苜蓿（苜蓿）幼苗关联期间细菌趋化性如何介导植物根表面定植。我们追踪了巴西 A. brasilense 在根际以及小麦和苜蓿根表面的积累。 A. brasilense 运动细胞在根的不同区域表现出不同的趋化行为，包括最终驱动表面定殖模式的引诱和驱避反应。我们还将这些观察结果与野生型和突变株行为的实时分析相结合，将根分泌物中识别的不同化学物质的趋化反应与特定的化学感受器联系起来，共同解释根部不同区域运动细胞的趋化反应。此外，细菌第二信使 c-di-GMP 调节这些趋化反应。总之，这些发现说明了细菌对指导根表面定植的根际梯度的动态趋化反应。重要性植物根系分泌物在塑造根际微生物群落中发挥着关键作用，而运动细菌对这些梯度做出反应的能力介导了根表面的竞争性定植。根系分泌物是复杂的化学混合物，在空间和时间上都是动态的。因此，确定介导土壤细菌招募到根部特定区域的确切化学物质具有挑战性。在这里，我们将细菌趋化反应和化学感受器感知的模式与根系分泌物梯度中发现的化学物质联系起来，并确定了在不同植物和根部区域中形成根表面定植的关键化学信号。
Plant root exudates play critical roles in shaping rhizosphere microbial communities, and the ability of motile bacteria to respond to these gradients mediates competitive colonization of root surfaces. Root exudates are complex chemical mixtures that are spatially and temporally dynamic. Identifying the exact chemical(s) that mediates the recruitment of soil bacteria to specific regions of the roots is thus challenging. Here, we connect patterns of bacterial chemotaxis responses and sensing by chemoreceptors to chemicals found in root exudate gradients and identify key chemical signals that shape root surface colonization in different plants and regions of the roots. ABSTRACT Plant roots shape the rhizosphere community by secreting compounds that recruit diverse bacteria. Colonization of various plant roots by the motile alphaproteobacterium Azospirillum brasilense causes increased plant growth, root volume, and crop yield. Bacterial chemotaxis in this and other motile soil bacteria is critical for competitive colonization of the root surfaces. The role of chemotaxis in root surface colonization has previously been established by endpoint analyses of bacterial colonization levels detected a few hours to days after inoculation. More recently, microfluidic devices have been used to study plant-microbe interactions, but these devices are size limited. Here, we use a novel slide-in chamber that allows real-time monitoring of plant-microbe interactions using agriculturally relevant seedlings to characterize how bacterial chemotaxis mediates plant root surface colonization during the association of A. brasilense with Triticum aestivum (wheat) and Medicago sativa (alfalfa) seedlings. We track A. brasilense accumulation in the rhizosphere and on the root surfaces of wheat and alfalfa. A. brasilense motile cells display distinct chemotaxis behaviors in different regions of the roots, including attractant and repellent responses that ultimately drive surface colonization patterns. We also combine these observations with real-time analyses of behaviors of wild-type and mutant strains to link chemotaxis responses to distinct chemicals identified in root exudates to specific chemoreceptors that together explain the chemotactic response of motile cells in different regions of the roots. Furthermore, the bacterial second messenger c-di-GMP modulates these chemotaxis responses. Together, these findings illustrate dynamic bacterial chemotaxis responses to rhizosphere gradients that guide root surface colonization. IMPORTANCE Plant root exudates play critical roles in shaping rhizosphere microbial communities, and the ability of motile bacteria to respond to these gradients mediates competitive colonization of root surfaces. Root exudates are complex chemical mixtures that are spatially and temporally dynamic. Identifying the exact chemical(s) that mediates the recruitment of soil bacteria to specific regions of the roots is thus challenging. Here, we connect patterns of bacterial chemotaxis responses and sensing by chemoreceptors to chemicals found in root exudate gradients and identify key chemical signals that shape root surface colonization in different plants and regions of the roots.