Plant-microbe interactions: Understanding the signal loop for improved plant productivity

植物总是与一个多样化和精心安排的微生物群落——植物微生物组联系在一起。这些微生物中的许多为相关植物提供有益的服务。在豆科植物中，固氮根瘤菌能够感染根组织，导致根瘤的分化（在一些豆科植物中是确定的根瘤，而在另一些中是不确定的根瘤），其中经过修饰的根瘤菌细胞从空气中吸收氮并将其提供给植物。通过豆科植物与根瘤菌共生的生物固氮提供了一种极其重要的低投入和环境友好的氮素获取途径，否则将作为化肥供应。越来越清楚的是，植物微生物组中的其他细菌能够协助固氮共生的建立和/或功能。这些促进菌株能够促进豆科植物固氮共生的建立和功能。在这项工作中，我们将评估两种潜在的促进菌株的能力，这两种菌株都是我们实验室分离出来的，以增强加拿大两种最重要的豆科作物大豆和豌豆的结瘤、固氮能力和生长。这两种植物特别令人感兴趣，因为它们代表了豆科植物结瘤的两种主要形式，即确定型（大豆）和不确定型（豌豆）结瘤。在根瘤菌和豆科植物之间的关系中，根瘤菌细菌的行为受到来自植物根系的物质的调节，并且越来越清楚的是，许多与根相关的微生物也同样受到相关植物的调节。我们将评估根分泌物的影响，以及其中包含的物质，以影响促进菌株的有益方面。我们还将确定促进菌株在根瘤中的长期存在和影响，以及它们改变植物蛋白表达、代谢和生理的能力。最后，利用宏观和微观CT扫描技术（CT：计算机断层扫描），确定对根分枝和根瘤发生及后续发展速度的影响。加强结瘤和固氮将使加拿大作物生产系统减少对氮肥的依赖。预计这将大大减少作物生产的能源投入、地面和地表水污染（硝酸盐）以及与作物生产有关的温室气体排放（氮肥产生的一氧化二氮）。大豆和豌豆是加拿大最广泛生产的两种豆科植物，加拿大是世界上最大的干豌豆生产国，因此这项研究将通过农业部门为加拿大提供直接利益。这项拟议的研究将使加拿大成为使用促进菌株技术以提高可持续作物生产的世界领先者，从而导致技术发展和加拿大技术的全球商业化。

A plant is always associated with a diverse and carefully orchestrated community of microbes the phytomicrobiome. Many of these microbes provide beneficial services to the associated plant. In the case of legumes, nitrogen fixing rhizobia are able to infect root tissues, leading to the differentiation of root nodules (in some legumes determinate nodules and in others indeterminate), where modified rhizobial cells take nitrogen from the air and supply it to the plant. Biological nitrogen fixation through the legume-rhizobia symbiosis provides an extremely important low-input and environmentally friendly access to nitrogen, otherwise supplied as chemical fertilizer. It is becoming clear that other bacteria in the phytomicrobiome are able to assist in the establishment and/or function of the nitrogen fixing symbiosis. These facilitator strains area able to promote both establishment and function of the legume nitrogen fixing symbiosis. In this work, we will evaluate the ability of two potential facilitator strains, both isolated by our laboratory, to enhance the nodulation, nitrogen fixing capacity and growth of Canada's two most important legume crops, soybean and pea. These two plants are of particular interest because the represent the two main forms of legume nodulation, these being determinate (soybean) and indeterminate (pea) nodules. In the relationship between rhizobia and legumes the behaviour of the rhizobial bacterium is regulated by materials from the plant roots, and it is becoming clear that many root-associated microbes are similarly regulated by the associate plants. We will evaluate the effects of root exudates, and materials contained within them, to affect the beneficial aspects of the facilitator strains. We will also determine the long-term presence and affects of the facilitator strains within nodules, and their ability to alter plant protein expression, metabolism and physiology. Finally, using macro- and micro-CT scanning technologies (CT: computed tomography), to determine the effects on root branching and rate of nodule initiation and subsequent development. Enhanced nodulation and nitrogen fixation will allow reduced reliance on fertilizer nitrogen in Canadian crop production systems. This is expected to substantially reduce the energy inputs into crop production, ground and surface water pollution (nitrate), and the greenhouse gas emissions associated with crop production (nitrous oxide derived from nitrogen fertilizer). Soybean and pea are the two most widely produced legumes in Canada and Canada is the world's largest producer of dry pea so that this research will provide direct benefit to Canada through the agriculture sector. This proposed research will make Canada a world leader in the use of facilitator strains technologies to enhance sustainable crop production, leading to technology development and global commercialization of Canadian technologies.