COLLABORATIVE PROJECT: Defining Plant Signals That StructureMicrobial Communities in the Rhizosphere

根上和根附近的天然细菌有助于植物生长，但对特定细菌物种如何在根际形成群落知之甚少。因此，阐明植物微生物信号的分子基础，确定其在细菌生长、存活和根定植中的作用是非常重要的。最近的研究结果表明，少量的某些植物化合物可以调节根瘤菌和农杆菌感染所需基因的转录。据推测，这些细菌中的其他植物诱导基因控制着根定植的早期阶段，而其他根际微生物中也存在同源基因。该项目将以根瘤菌和农杆菌为模型，寻找新的植物调控基因，这对理解根际生物学的更广泛问题很重要。通过超越这些生物中已被充分研究的结瘤和毒力基因，希望为未来的根际生态学研究奠定基础。该项目将1)确定植物信号的化学结构，诱导土壤细菌中的基因；2)分离出对这些化合物有反应的新细菌基因；3)推断信号转导途径；4)评估这些分子作为土壤中微生物定植调节剂的重要性。这些目标将通过鉴定苜蓿（Medicago sativa L.）中诱导随机生物发光（lux）基因融合转录的自然信号来实现。该项目的工具和经验可在三位联合首席研究员的补充项目中获得。菲利普博士多年来一直在研究根瘤菌与豆科植物的相互作用，并使用现代方法分离和鉴定这种共生关系中涉及的化合物。Drs。Kado和de Bruijn是经验丰富的微生物遗传学家，主要研究农杆菌和根瘤菌。该项目将从分子角度定义苜蓿是如何通过两种模式土壤微生物控制根系定植的，并将开发信息和工具，用于测试有关根际微生物群落结构生理过程的详细假设。这是我和密歇根州立大学的de Bruijn博士的合作研究项目。＊＊＊

9218567 Phillips Natural bacteria on and near roots contribute to plant growth, but little is known about how particular bacterial species form communities in the rhizosphere. Therefore, it is important to clarify the molecular basis of plant-microbe signaling and define its role in bacterial growth, survival, and colonization of roots. Recent results show that small quantities of certain plant compounds regulate transcription of genes required for infection by Rhizobium and Agrobacterium bacteria. It is postulated that other plant-induced genes in these bacteria control earlier stages of root colonization and that homologous genes are present in other rhizosphere microbes. This project will use Rhizobium and Agrobacterium as models to find novel plant-regulated genes that are important for understanding broader issues of rhizosphere biology. By moving beyond the well-studied nodulation and virulence genes in these organisms, it is hoped to build a basis for future research on rhizosphere ecology. This project specifically will 1) define chemical structures of plant signals that induce genes in soil bacteria, 2) isolate novel bacterial genes responding to the compounds, 3) deduce signal transduction pathways, and 4) assess the importance of the molecules as regulators of microbial colonization in the soil. These goals will be achieved by identifying natural signals from alfalfa (Medicago sativa L.) which induce transcription of random bioluminescence (lux) gene fusions in R. meliloti and A. tumefaciens. The tools and experience for this project are available in the complementary programs of the three co-principal investigators. D. A. Phillips has studied Rhizobium-legume interactions for many years and uses modern methods to isoate and identify compounds involed in that symbiosis. Drs. Kado and de Bruijn are experienced microbial geneticists with major research programs on Agrobacterium and Rhizobium. This project will define in molecular terms how alfa lfa controls root colonization by two model soil microbes, and it will develop information and tools required for testing detailed hypotheses on physiological processes that structure microbial communities in the rhizosphere. This is a collaborative research project with Dr. de Bruijn at Michigan State University. ***