BRC-BIO: Familiarity with friends: Transgenerational effects as a mechanism for partner choice in the legume-rhizobia mutualism

互惠关系具有根本性的重要性，可以在每一个生物体层面上发现，在那里它们有助于相互作用的伙伴的健康和生存。例如，氮是植物生长所需的基本营养物质，但最丰富的形式是植物无法获得的，这使得它成为一种有限的资源。豆类通过与被称为根瘤菌的共生细菌形成有益的伙伴关系，克服了这一限制，在根瘤菌中，它们获得可用氮，以换取碳代谢物。问题是，在建立关系之前，工厂没有关于合作伙伴质量的信息。在排除寄生细菌的同时，选择正确的互惠细菌伙伴是至关重要的，因为形成互惠关系的过程需要植物消耗本来可以用于生长的能量。许多豆科植物已经表现出一定程度的专一性，利用信号来限制与亲和根瘤菌的伙伴关系。一旦启动这种伙伴关系，就会有额外的分子信号触发植物免疫系统。任何一种类型的信号都可能在寄主植物上留下特定于单个根瘤菌菌株的印记或记忆。本研究检验了这种记忆可能是可遗传的假设，并帮助寄主植物的后代由于熟悉而选择有益的品系，从而更好地理解非遗传遗传性，并为维持互惠关系提供洞察力。该项目还为本科生提供了资助的研究经验，这已被证明提高了STEM的多样性和保留率。互惠关系的产生和维持是一个进化难题，因为双方都被期望以自己的利益行事。就像所有的互惠关系一样，主人有被他们的伴侣利用导致关系破裂的风险。能够选择一个忠诚的、有益的伴侣可以使伙伴关系稳定下来。然而，尽管有证据表明寄主植物能够优先与更有益的伙伴结瘤，但豆科植物-根瘤菌互惠关系中允许选择伴侣的机制尚未被发现。这个项目检验了所选择的伙伴可能由遗传(寄主植物和根瘤菌基因)、表观遗传和环境因素组合决定的预测。利用有胡子的三叶草，研究小组将确定前几代人的跨代效应是否会影响寄主植物对共生伙伴的选择。该项目将量化根瘤占有率，以确定以前接触一种菌株及其效力是否会影响宿主植物的选择，使用荧光标记、qPCR和元生物编码来区分菌株水平上的根瘤菌。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Mutualisms are of fundamental importance and found at every organismal level, where they facilitate the fitness and survival of the interacting partners. For example, nitrogen is an essential nutrient required for plant growth, yet the most abundant form is inaccessible to plants, making it a limiting resource. Legumes have overcome this limitation by forming beneficial partnerships with symbiotic bacteria, known as rhizobia, where they receive usable nitrogen in exchange for carbon metabolites. The problem is that prior to establishing the relationship, the plant has no information about the quality of its partner. Choosing the right mutualistic bacterial partner, while excluding parasitic bacteria, is essential because the process to form the mutualistic relationship requires the plant to expend energy that could otherwise be used for growth. Many legume species already show some degree of specificity using signaling to limit partnership with compatible rhizobia species. Once the partnership is initiated, there is additional molecular signaling that triggers the plant immune system. Either type of signaling may leave an imprint or memory on the host plant that is specific to individual rhizobia strains. This study examines the hypothesis that this memory may be heritable and help future generations of the host plant choose beneficial strains due to familiarity, giving a better understanding of non-genetic heritability and providing insight into the maintenance of mutualistic relationships. This project also provides undergraduate students with funded research experience, which has been shown to improve diversity and increase retention in STEM.The origination and maintenance of mutualisms presents an evolutionary conundrum as both partners are expected to act in their own self-interest. As with all mutualisms, there is a risk of the host being exploited by their partner leading to the breakdown of the relationship. The ability to choose a faithful and beneficial partner can stabilize the partnership. However, the mechanism that allows for partner choice has not yet been uncovered in the legume-rhizobia mutualism, despite evidence that host plants are able to preferentially nodulate with more beneficial partners. This project examines the prediction that the selected partner will likely be determined through a combination of genetic (host plant and rhizobia genes), epigenetic and environmental elements. Using the bearded clover, Trifolium barbigerum, the research team will determine whether transgenerational effects from previous generations can influence the host plant’s choice of symbiotic partner. This project will quantify nodule occupancy to determine whether previous exposure to a strain and its efficacy inform host plant selection using a combination of fluorescent labeling, qPCR and metabarcoding to distinguish rhizobia at the strain level.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.