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

氮(N)虽然在大气中含量丰富，但却是许多植物生长最受限制的养分之一。现代农业依赖于化学氮肥，而化学氮肥会造成广泛的环境破坏，而且是不可持续的。与大多数作物不同，豆科植物（如大豆、蚕豆、扁豆、苜蓿）与土壤细菌形成共生关系，形成根瘤，细菌在根瘤中大量积累，为植物固定大气氮。由于固氮能力，豆科植物在农业和自然环境的可持续性中发挥着重要作用。然而，许多豆科树木不形成根瘤，因此被认为是非固氮的。许多非结瘤豆科植物是各种生态系统的重要组成部分，越来越多地被用于土地复垦和生物燃料作物。增加对非结瘤豆科植物获得氮的机制的了解对于提高这些豆科植物在营养贫乏土壤中的利用至关重要。该项目将为本科生和博士后提供微生物和植物生物学方面的培训机会，特别是在植物与微生物相互作用方面。在密尔沃基大学的城市农业倡议中，也将强调微生物共生研究的好处。到目前为止，豆科植物是原始环境中生物固定氮的最大贡献者。虽然结瘤通常被认为是豆科植物的一个显著特征，但大量的物种不知道结瘤。非结瘤豆科植物与其结瘤“表亲”生活在相同的自然环境中，但植物氮浓度相同。然而，对非结瘤豆科植物的氮获取机制知之甚少。本项目将探讨非结瘤豆科蜜刺槐（Gleditsia triacanthos L.）与根瘤菌共生固氮的可能性。来自研究者实验室的初步数据显示，在三棘草的根上存在含有根瘤菌的结节状结构。本项目将(i)阐明根瘤菌在三叶甘露中的定植程度和机制，（ii）确定三叶甘露对根瘤菌感染的反应，（iii）确定三叶甘露-根瘤菌结合中氮固定的潜力。从长远来看，该项目的结果可以为改善非豆科植物的氮营养铺平道路，包括不形成固氮共生的谷类作物。

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.