Identification of two early acting plant genes in the mycorrhizal symbiosis

碳、氮和磷是蛋白质和DNA的三种主要成分，因此这三种元素对生命至关重要。哺乳动物通过食用植物或其他动物获得这些营养。另一方面，植物必须从它们周围的环境中获取这些营养。植物已经发展出许多与微生物有益的相互作用，促进了碳、氮和磷的吸收。植物的光合作用，利用太阳的能量将大气中的二氧化碳转化为糖，是与光合细菌相互作用的结果。这种相互作用是如此先进，以至于细菌不再能够以自由生活的状态存在，而是被转化为植物细胞内称为叶绿体的隔间。此外，大多数植物与菌根真菌形成相互作用，菌根真菌侵入植物根部，在土壤中生长，帮助植物吸收营养物质，特别是磷酸盐。此外，一些植物物种，特别是豆科植物（豌豆和豆类），已经进化出与固氮细菌的相互作用，将大气中的氮转化为植物容易获得的形式。菌根真菌和固氮细菌的相互作用对植物和微生物都是有益的：植物接受营养氮和磷酸盐，以交换通过光合作用产生的糖。因此，植物可以被描述为一个商人，它从与光合细菌的古老相互作用中获得碳，从与菌根真菌和固氮细菌的相互作用中获得氮和磷酸盐。植物和微生物的共同进化创造了复杂的相互作用，在许多情况下，生物体可以完全依赖于相互作用来生存：例如菌根真菌无法在没有植物宿主的情况下生存。为了建立这些相互作用，植物和微生物之间有广泛的分子交流。植物向土壤释放化学信号，这些信号被相应的真菌和细菌识别。反过来，细菌和真菌向植物释放化学信号，诱导植物激活适应微生物所需的发育过程。在植物中有一个单一的分子途径需要识别真菌和细菌的信号。这是令人惊讶的，因为固氮细菌在植物中诱导的发育过程与菌根真菌诱导的发育过程非常不同。因此，尽管在早期信号通路中存在这种共性，但植物必须仍然能够区分真菌和细菌。支持这一观点的事实是，在细菌相互作用中，有许多基因具有特定的作用，它们提供共同信号通路的特定输入和输出。我们最近发现了两个只需要真菌相互作用的基因。在这个提议中，我们将测试这些是否代表真菌对共同信号通路的特定输入，此外，我们将破译基因身份，以更好地了解植物如何能够感知菌根真菌的存在。这项工作将帮助我们了解这种重要的相互作用是如何建立的，并将帮助我们了解植物如何能够区分菌根真菌和固氮细菌。

Carbon, nitrogen and phosphorus are the three major ingredients for proteins and DNA and as such these three elements are essential for life. Mammals acquire these nutrients through eating plants or other animals. Plants on the other hand must acquire these nutrients from the environment around them. Plants have developed a number of beneficial interactions with micro-organisms that facilitate the uptake of carbon, nitrogen and phosphorus. Photosynthesis in plants, that utilises the suns energy to convert carbon dioxide in the atmosphere to sugars, is the result of an ancient interaction with photosynthetic bacteria. This interaction is so advanced that the bacteria are no longer able to exist in a free-living state, but have been converted into compartments within the plant cell called chloroplasts. In addition, most plants form an interaction with mycorrhizal fungi that invade the plant root and grow through the soil and help the plant take up nutrients particularly phosphates. Furthermore, a selection of plant species, particularly legumes (peas and beans), have evolved an interaction with nitrogen fixing bacteria that convert atmospheric nitrogen into a form readily available to the plant. The mycorrhizal fungi and nitrogen fixing bacterial interactions are beneficial to both the plant and the micro-organism: the plant receives the nutrients nitrogen and phosphate in exchange for sugars generated through photosynthesis. As such the plant can be described as a merchant that trades carbon from an ancient interaction with photosynthetic bacteria for nitrogen and phosphates from interactions with mycorrhizal fungi and nitrogen fixing bacteria. The co-evolution of the plant and the microbe has created complex interactions and in a number of cases the organisms can be entirely dependent upon the interaction for survival: for instance mycorrhizal fungi are unable to live in the absence of the plant host. In order to establish these interactions there is extensive molecular communication between the plant and the micro-organism. Plants release chemical signals into the soil that are recognised by the appropriate fungi and bacteria. In turn the bacteria and fungi release chemical signals to the plant that induce the plant to activate the developmental processes required to accommodate the micro-organisms. There is a single molecular pathway in the plant that is required to recognise both the fungal and bacterial signals. This is surprising since the developmental processes that are induced in the plant by nitrogen fixing bacteria are very different to the developmental processes induced by the mycorrhizal fungi. Hence, despite this commonality in the early signalling pathways the plant must still be able to discriminate between the fungus and the bacteria. In support of this is the fact that there are a number of genes with specific roles in the bacterial interaction that provide specific inputs and outputs of the common signalling pathway. We have recently identified two genes that are only required for the fungal interaction. In this proposal we will test whether these represent fungal specific inputs into the common signalling pathway and in addition we will decipher the gene identities to better understand how the plant is able to perceive the presence of the mycorrhizal fungus. This work will help us understand how this important interaction is established and will aid us in understanding how the plant is able to discriminate between mycorrhizal fungi and nitrogen fixing bacteria.