Research Accomplishment Reports 2011

Plant-Microbe Communication in the Medicago truncatula Rhizosphere: Functional Metagenomics, Biochemistry, and Community Analysis

L.A. Moe
Department of Plant and Soil Sciences

 

Non-Technical Summary

egumes (Fabaceae) comprise one of the largest and most diverse families of vascular plant on the planet, with an estimated 18,000 species spread across all continents except for Antarctica. The Papilionoidaea legume subfamily includes the majority of legumes of agronomic value, such as alfalfa, soybean, chickpea, garden pea, and lentil. Estimates of the dietary intake of legumes show that this family is responsible for ~1/3 of the total protein intake in the human diet. In addition to their human dietary importance, certain legumes (e.g. alfalfa) are major forage crops important in sustaining livestock agriculture worldwide.

Most legume species have the ability to form symbioses with nitrogen-fixing bacteria. This is an unusual yet important feature, shared among few plants outside the legume family, enabling them to thrive in environments with minimal nitrogen input. Due to their nitrogen-fixing ability, they are also used as a rotation crop to enhance available soil nitrogen. Barrel medic (Medicago truncatula) has been studied extensively as a model legume since the 1990s, and work on this plant and its associated microbiota has resulted in significant advances in understanding of the basic biology of the legume, mechanisms of plant-microbe communication, and the biology of symbiotic nitrogen fixation.

It is now recognized that bacteria and fungi accumulate in large, diverse populations at the plant root-soil interface (the rhizosphere). This microbial community accumulates to take advantage of the rich collection of nutrients secreted by the plant roots (plant root exudate). Some plant root exudate chemicals are demonstrated to act as signals to specific microbes. These signals can result in alterations to the rhizosphere microbial community that enhance plant nutrient uptake, aid in suppression of plant pathogens, and enable a symbiotic relationship between plant and microbe resulting in nitrogen fixation by certain bacteria in legume plant root nodules.

We aim to identify genetic features of the plant that enable optimal microbial community assembly in the Medicago truncatula rhizosphere. While our work will be done with a legume, we strongly believe that the research will be relevant to rhizosphere microbial community assembly and function in all agriculture crops.

This work will result in an increased knowledge of signaling pathways between plant and microbe that enhance plant health, plant productivity and sustainability of the agricultural system. Ultimately, crop breeders and plant genetic engineers will use knowledge generated from this research to select for crop varieties that will optimize their rhizosphere microbial community to enhance these features.