Mechanisms linking bacterial chemotaxis signaling to nitrogen fixation in beneficial plant-associated bacteria

细菌接种剂可以提高作物产量，减少对昂贵且对环境有害的化肥的依赖，而到2050年，全球预计将有97亿人口需要这些化肥来满足粮食需求。细菌接种剂不仅要表现出对植物生长有益的性状，而且要能够在植物根部定殖，才能在田间应用。此外，许多在实验室中选择作为生物接种剂的细菌一旦应用于温室或田间，就不能持续地产生植物生长促进作用。这突出了我们对根际有益细菌的行为和生理的理解的不足。本项目旨在阐明生物接种菌协调植物生长有益性状（固氮）与根际竞争和植物根系定植（趋化性）关键功能表达的分子机制。从本研究中获得的知识将有助于建立更好的预测模型，以指导选择和/或设计用于生物接种应用的有益重氮营养物的策略，以改善作物管理，造福社会。除了通过基础研究解决与可持续农业相关的挑战外，该项目还将吸引不同社区的参与者参与制定应对这些挑战的未来解决方案。该项目将为高中生和本科生提供研究机会，包括来自代表性不足群体的成员，在适当的情况下，这些学生将被纳入出版物的共同作者。首席研究员还将继续让耳聋和听力障碍的本科生参与研究经验。该项目还将为研究生和博士后提供指导本科生的机会，并在广泛的推广活动中应用他们的研究沟通技巧。初步数据表明，细菌趋化信号蛋白可调节有益植物定植和生物接种重氮营养菌巴西氮螺旋菌的固氮表达。研究人员旨在利用遗传学、活细胞荧光显微镜和生化方法，确定细菌趋化信号蛋白协调诱导重氮营养土壤细菌固氮的分子机制，以及这种偶联在根际中的作用。他们还将探索豌豆共生体豆科根瘤菌（Rhizobium leguminosarum bv）代谢和趋化信号之间明显类似的耦合机制。viciae。目的1将建立趋化性信号控制巴西芽孢杆菌氮代谢的机制，并具体验证趋化性信号蛋白与能量响应蛋白相互作用影响固氮转录调控因子RpoN表达的假设。小麦根际固氮表达的时空格局以及趋化性如何影响这一活动也将被确定。目的2将揭示一组趋化受体如何调节趋化性信号以支持巴西芽孢杆菌在小麦根际的固氮。氧和能量感应化学受体在影响趋化性、感觉特异性、固氮和根定植中的作用将被表征。此外，这些化学受体之一在维持趋化性信号阵列结构完整性中的作用将被阐明。目的3将探讨受营养饥饿影响的趋化信号阵列组成如何调控豆科植物固氮结瘤。总之，获得的结果将为了解不同的分子功能（趋化性和氮代谢）如何进化成细胞内的整合提供洞见。这些发现还将通过阐明控制有助于根际植物生长促进能力的性状的一般设计原则，为提高重氮营养生物接种剂的性能提供策略。该研究将采用与现代农业相关的遗传可处理模型系统来解决紧迫的环境问题和可持续农业实践。本研究的结果将有助于建立更好的预测模型，以指导选择和/或设计用于生物接种应用的有益重氮营养体的策略。该奖项是由分子和细胞生物科学部的细胞动力学和功能集群以及综合有机系统部的植物生物相互作用项目共同资助的。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Bacterial inoculants can enhance crop yields and reduce reliance on expensive and environmentally harmful chemical fertilizers which are needed to meet the demand for food of the expected global population of 9.7 billion by 2050. To be useful in the field, bacterial inoculants must not only express plant growth beneficial traits but must also be able to colonize plant roots. Further, many bacteria selected in the laboratory as bio-inoculants fail to consistently produce plant growth enhancements once applied in greenhouses or in the fields . This highlights shortcomings in our understanding of the behavior and physiology of beneficial bacteria in the rhizosphere. This project aims to elucidate the molecular mechanisms by which bio-inoculant bacteria coordinate expression of plant growth beneficial traits (nitrogen fixation) with functions that are critical for competitiveness in the rhizosphere and colonization of plant roots (chemotaxis). The knowledge gained from this research will contribute toward better predictive models to guide strategies to select and/or design beneficial diazotrophs for bio-inoculation applications, to improve crop management with benefits to society. In addition to addressing challenges related to sustainable agriculture through basic research, the project will engage a diverse community of participants in developing future solutions to these challenges. The project will provide research opportunities for high school and undergraduate students, including members from underrepresented groups, with those students included as co-authors in publications, when appropriate. The principal investigator will also continue engagement of deaf-and-hard-of-hearing undergraduate students in research experiences. The project will also provide graduate students and a postdoctoral fellow with opportunities to mentor undergraduate students and to apply their research communication skills in a breadth of outreach activities.Preliminary data suggest that bacterial chemotaxis signaling proteins regulate the expression of nitrogen fixation in the beneficial plant-colonizing and bio-inoculant diazotroph, Azospirillum brasilense. The investigators aim to determine the molecular mechanisms by which bacterial chemotaxis signaling proteins coordinate the induction of nitrogen fixation in diazotroph soil bacteria used as biofertilizers worldwide, and the role of this coupling in the rhizosphere, using genetics, live cell fluorescence microscopy and biochemical approaches. They will also explore the mechanism of an apparent similar coupling between metabolism and chemotaxis signaling in the pea symbiont, Rhizobium leguminosarum bv. viciae. Objective 1 will establish the mechanism(s) of chemotaxis signaling control of nitrogen metabolism in A. brasilense and specifically test the hypothesis that chemotaxis signaling proteins interact with an energy-responsive protein(s) to affect the expression of a transcriptional regulator of nitrogen fixation, RpoN. The spatio-temporal pattern of nitrogen fixation expression in the wheat rhizosphere and how chemotaxis affects this activity will also be determined. Objective 2 will decipher how a subset of chemoreceptors adjust chemotaxis signaling to support A. brasilense nitrogen fixation in the wheat rhizosphere. The role of oxygen- and energy-sensing chemoreceptors in affecting chemotaxis sensory specificity, nitrogen fixation and root colonization will be characterized. In addition, the role of one of these chemoreceptors in maintaining chemotaxis signaling arrays structural integrity will be elucidated. Objective 3 will explore how chemotaxis signaling array composition, which is affected by nutrient starvation, regulates nitrogen-fixing nodulation in R. leguminosarum. Together, the results obtained will provide insight into how distinct molecular functions (chemotaxis and nitrogen metabolism) evolved to become integrated within cells. These findings will also produce strategies to improve the performance of diazotroph bioinoculants by elucidating general design principles for the control of traits that contribute to rhizosphere plant-growth promoting competence. The research will employ genetically tractable model systems relevant to modern agriculture to address pressing environmental issues and sustainable agricultural practices. The results of this research will contribute toward better predictive models to guide strategies to select and/or design beneficial diazotrophs for bio-inoculation applications. This award is being co-funded by the Cellular Dynamics and Function cluster in the Division of Molecular and Cellular Biosciences, along with the Plant Biotic Interactions program in the Division of Integrative Organismal Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.