Functional Genomics of Root Hair Infection

University Of Missouri-Columbia, Columbia MO

Investigators

Abstract

Root hairs are specialized, single cell organs that develop on roots to increase surface area and enhance nutrient and water uptake. These cells are also the site of infection of legumes by symbiotic nitrogen fixing bacteria. This latter process involves extensive cellular changes in the root hair with the formation of an infection thread by which the bacteria gain entry into the root cortex. This process culminates in the formation of a novel organ, the nodule, in which the bacteria fix atmospheric nitrogen. The net result is a system by which the bacteria gain a nutritious environment, while the plant gains access to nitrogen, commonly a limiting nutrient for plant growth. Thus, the rhizobial infection process has great agronomic and ecological significance. Moreover, the infection process, especially during the early phases within the root hair, presents interesting cell biology questions. The research will focus on root hair infection by rhizobia, a poorly characterized and experimentally difficult step in the symbiosis to study. The research is made possible by using soybean, from which we can isolate purified root hairs in gram quantities; an amount enabling the application of both DNA microarray and proteomic analysis. At a more basic level, the research allows for the detailed analysis, using modern functional genomic tools, of the cell biology of a single, plant cell type. Microarray data obtained will be submitted to the GEO database and will be made publicly available upon acceptance of the relevant manuscript for publication. The function of genes identified by functional genomic analysis will be further analyzed by specific silencing using RNAi technology. We will also employ a comparative approach using the large and growing collection of symbiotically defective plant mutants in the model legumes, M. truncatula and L. japonicus. Publications arising from the work will detail methods and results to the larger scientific community. Broader Impacts The research involved will impact education at all levels: high school, undergraduate, graduate and postgraduate. Specifically, in order to reach more undergraduate students, we intend to use a distance learning method by which students, at their home institutions, design DNA microarray experiments, which then are conducted in our laboratories. The students will then have access to the data via a dedicated website. In this way, we will bring DNA microarray resources to the development of undergraduate biology curriculum. The work proposed has broader biological significance since it represents one of the few systems in which the cell biology of a single cell type, the root hair, can be studied in detail. We expect our research to address important basic questions relevant to plant cell biology; such as, polar cell growth, cytoskeleton dynamics, calcium signaling, and many others. In order to translate plant genomic knowledge into crop improvement, genomic knowledge of crop plants, such as soybean, must be developed well enough to allow information transfer from models to occur. Our research will contribute to the development of soybean functional genomics and comparative legume genomics. The increasing knowledge base of soybean biology will allow plant scientists to respond to new threats and opportunities that may impact this agronomically important species in the future. The further development of the genomics of many plant species, including soybean, will accommodate comparative approaches and will provide synergistic opportunities to advance plant science. The training provided by the research described will help prepare the next generation of plant scientists to meet these challenges.