EAGER: Elucidating Rhizobial Interactions and the Possibility of Symbiotic Nitrogen Fixation in Non-nodulating Legume Gleditsia Triacanthos L.

University Of Wisconsin-Milwaukee, Milwaukee WI

Investigators

Abstract

Nitrogen (N) is one of the most limiting nutrients for the growth of many plants though it is abundant in the atmosphere. Modern agriculture depends upon chemical N fertilizers that cause extensive environmental damage and are not sustainable. In contrast to the majority of crops, legumes (such as soybean, bean, lentils, alfalfa) form symbiotic associations with soil bacteria, resulting in the formation of nodules in which the bacteria accumulate in high numbers and fix atmospheric N for the plant. Because of N-fixing ability, legumes play an important role in sustainability in both agricultural and natural environments. However, many tree legumes do not form nodules and are thus considered non-N fixing. Many non-nodulating legumes are important components of various ecological systems and are increasingly being used for land reclamation and as biofuel crops. Increased understanding of the mechanisms by which non-nodulating legumes obtain their nitrogen will be crucial in improving the utilization of these legumes in nutrient-poor soils. The project will provide opportunities to undergraduate students and a post-doctoral fellow to train in both microbial and plant biology, especially as they relate to plant-microbial interactions. The benefits of research on microbial symbioses will also be emphasized in the urban agriculture initiative at UW Milwaukee. Legumes are by far the largest contributors of biologically fixed N2 to pristine environments. Although nodulation is often considered to be a distinguishing characteristic of legumes, a large number of species are not known to nodulate. Non-nodulating legumes live in the same native environments as their nodulating 'cousins' and yet have the same in planta N concentrations. Very little , however, is known about the mechanisms of N-acquisition in non-nodulated legumes. This project will explore the hypothesis that non-nodulating legume honey locust (Gleditsia triacanthos L.) possesses the potential for symbiotic N2 fixation with rhizobia. Preliminary data from the investigator's laboratory shows the presence of nodule-like structures on the roots of G. triacanthos that contained rhizobia. This project will (i) Elucidate the extent and mechanism of rhizobial colonization in G. triacanthos, (ii) Determine the response of G. triacanthos to rhizobial infection and (iii) Determine the potential of N2-fixation in the G. triacanthos-rhizobial association. In the long term, the results of this project could pave the way to improve N nutrition of non-legumes, including cereal crops that do not form N-fixing symbiosis.