Molecular Strategies for adaptation by legumes to toxic environments

Anthropogenic changes to environments can impose immediate stress on native plants, animals and microbes. The symbiotic interactions between legume species and nitrogen fixing soil bacteria have profound impacts on soil quality, plant health, and both plants and soil microbes have potential for bioremediation of toxic soils. Legumes account for one-third of the world crop production and are among the most important foods for livestock in many countries and naturally occurring legume species provide ecosystem services by replenishing nitrogen into the soils. Because of their use as forage crops and general ecosystem services provided by nitrogen fixation, understanding how legume species deal with toxic heavy metals is of great importance. Identifying the genetic mechanisms whereby toxic metals can enter the food chain is of great importance for human health and environmental remediation. Adaptation can occur through new mutations or selection on existing alleles or standing genetic variation. The heavy metals cadmium and mercury are highly toxic to most organisms, so how plants and microbes tolerate these metals is of considerable interest to ecologists, evolutionary biologists, molecular biologists and agricultural scientists. Medicago truncatula has symbiotic interactions with soil borne nitrogen-fixing bacteria. When plant tissues become too toxic, the host environment is unsuitable to symbiotic microbes. Therefore, successful symbiosis depends on heavy metal detoxification and large effect alleles that increase metal accumulation would be deleterious. Gene expression data generated in this study was used to compared expression between low and tolerant plant genotypes and identify expression changes triggered by the heavy metals. Furthermore, because M. truncatula is the most important model species for all legumes, these data will be essential for identifying genes that are important in metal ion homeostasis in important crop species such as soybean and alfalfa.