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-微生物信号传导的分子基础并确定其在细菌生长、存活和根定殖中的作用是重要的。 最近的研究结果表明，少量的某些植物化合物调节根瘤菌和土壤杆菌感染所需的基因的转录。 据推测，其他植物诱导的基因在这些细菌控制根定植的早期阶段，同源基因存在于其他根际微生物。 该项目将使用根瘤菌和农杆菌作为模型，以寻找新的植物调控基因，这对理解更广泛的根际生物学问题很重要。 通过超越这些生物体中已被充分研究的促生长和毒性基因，希望为未来的根际生态学研究奠定基础。 该项目具体将1）定义诱导土壤细菌基因的植物信号的化学结构，2）分离响应化合物的新细菌基因，3）推断信号转导途径，4）评估分子作为土壤中微生物定殖调节剂的重要性。 这些目标将通过识别苜蓿（Medicago sativa L.）其诱导随机生物发光（lux）基因融合体在R. meliloti和苜蓿A.根瘤菌 该项目的工具和经验可在三个共同主要研究者的补充方案。 D. A.菲利普斯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参与共生的化合物。 Kado和de Bruijn博士是经验丰富的微生物遗传学家，主要研究项目是农杆菌和根瘤菌。 该项目将从分子水平上确定铝是如何通过两种模式土壤微生物控制根际定植的，并将开发测试关于构建根际微生物群落的生理过程的详细假设所需的信息和工具。 这是一个与加州大学戴维斯分校的菲利普斯博士和卡多博士合作的项目。 ***

9402659 deBruijn 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 isolate and identify compounds involved 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 al falfa 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 project with Drs. Phillips and Kado at the University of California, Davis. ***