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

氮(N)是许多植物生长最受限的营养物质之一，尽管它在大气中含量丰富。现代农业依赖于化学氮肥，这会造成广泛的环境破坏，而且是不可持续的。与大多数农作物不同，豆类(如大豆、豆类、小扁豆、紫花苜蓿)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，并为植物固定大气中的氮。由于豆类植物的固氮能力，在农业和自然环境中都发挥着重要的可持续性作用。然而，许多豆科树种不形成根瘤，因此被认为是不固氮的。许多非结瘤豆类是各种生态系统的重要组成部分，越来越多地被用于开垦土地和用作生物燃料作物。增加对非结瘤豆类植物获得氮素的机制的了解，对于改善这些豆类植物在养分贫乏的土壤中的利用至关重要。该项目将为本科生和博士后提供培训微生物和植物生物学的机会，特别是与植物-微生物相互作用有关的培训。密尔沃基大学密尔沃基分校的都市农业计划也将强调微生物共生研究的益处。到目前为止，豆类是对原始环境产生生物固定氮气的最大贡献者。虽然结瘤通常被认为是豆科植物的一个显著特征，但许多物种并不知道有结瘤。非结瘤豆科植物与其结瘤“表亲”生活在相同的原生环境中，但植物氮浓度相同。然而，人们对非根瘤豆科植物的氮素吸收机制知之甚少。本项目将探索非结瘤豆科植物刺槐(Gleditsia triacanthos L.)具有与根瘤菌共生固定氮气的潜力。来自研究人员实验室的初步数据显示，在含有根瘤菌的三棘豆根部存在结节状结构。本项目将(I)阐明三棘棉根瘤菌定植的范围和机制，(Ii)确定三棘棉对根瘤菌侵染的响应，(Iii)确定三棘棉-根瘤菌联合作用中固氮的潜力。从长远来看，该项目的结果可能为改善非豆类作物的氮素营养铺平道路，包括没有形成固氮共生关系的谷类作物。

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.