Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/6/2007
Publication Date: 6/7/2007
Citation: Samac, D.A., Graham, M.A. 2007. Recent advances in legume-microbe interactions: recognition, defense response, and symbiosis from a genomic perspective. Plant Physiology. 144:582-587. Interpretive Summary: Plants interact with a multitude of microorganisms in the environment. Interactions with mutualistic microbes are beneficial to both plant and microbe growth and reproduction while interactions with pathogenic microbes are detrimental to plant growth. Plants in the legume family form mutualistic relationships with specific bacteria that provide the plants with nitrogen compounds. Recent research indicates that plants use similar mechanisms to identify the mutualistic bacteria and pathogenic microbes. Legumes also restrict growth of mutualists and pathogens with similar chemical compounds. Current research in the area is focused on identifying genes that are common to interactions with mutualists and pathogens, as well as genes that are unique to one type of interaction. This research will help to understand how plants distinguish "friend" from "foe" and accelerate development of legume crop varieties with enhanced disease resistance.
Technical Abstract: The ability of legumes to form symbiotic mutualistic relationships with certain bacteria in the Rhizobiales (collectively called rhizobia) and harness the ability of the bacteria to "fix" atmospheric N2 into ammonia has had a tremendous impact on natural and agricultural ecosystems. The interaction has enabled legumes to produce protein-rich seeds and foliage that are critical to many human and animal diets. Past research has illuminated many of the facets of plant-bacterium recognition, nodule formation, nitrogen fixation, and ammonia assimilation. Less well understood are the mechanisms that allow bacterial colonization without triggering plant defense responses. Specifically, how do legumes recognize "friend" from "foe?" This Update examines clues to resolve this question arising from recent genomic research of model and crop legumes. Of particular interest are the roles of flavonoid compounds in legume-rhizobial and legume-pathogen interactions. Legumes are a rich source of flavonoids, notably the isoflavones and isoflavanones, which are not found in Arabidopsis. Legume nodules are also rich sources of cysteine cluster proteins, some of which have been shown to have antimicrobial activity, and may play a role in protecting nodules from pathogens.