Role of a 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase in Plant-Microbe Symbiotic Signaling Pathways

大豆、紫花苜蓿或花生等豆类植物具有与土壤细菌结合的独特能力，这种细菌被称为根瘤菌。这种共生导致根瘤的形成，在根瘤内，根瘤菌将空气中的氮转化为植物可吸收的形式。在美国，这种共生每年节省约45亿美元的化肥成本，并防止与过度使用化肥相关的生态和健康问题。根瘤菌与豆科植物的共生表现出高度的种特异性，即特定的豆科植物只与特定的根瘤菌相关。这种特异性机制主要由根瘤菌产生并被寄主植物识别的LCO(脂壳寡糖)信号的结构控制。LCoS还调节与共生真菌的关联，这种共生真菌不仅存在于豆类作物中，还存在于许多其他非豆类作物中，如玉米、小麦和棉花。LCoS现在被农民用作豆类和非豆类作物的植物生长促进剂。植物中的遗传分析可以鉴定与LCO受体相互作用的LCO受体和蛋白质，如HMGR1(3-羟基-3-甲基戊二酰辅酶A还原酶1)，这是建立共生联系所必需的。该项目将有助于更好地理解豆类识别共生LCoS的机制，以及允许LCO受体和HMGR1介导根瘤菌根瘤的发育以及与共生真菌的联系的下游途径。在短期内，了解这些机制可以通过更有效地利用LCoS作为植物生长促进剂来直接影响产量的提高。这一知识还将有助于改善植物-微生物协会的建立，尤其是在次优和紧张的田间条件下影响特别大。从长远来看，通过这些机制设计新的共生联盟可能有助于提高我们用于食品、饲料和生物燃料生产的农业的可持续性。

Legumes such as soybeans, alfalfa or peanuts have the unique ability to associate with soil bacteria named rhizobia. This symbiosis leads to the formation of root nodules inside which the rhizobia transform air nitrogen into forms assimilable by the plant. Every year, in the United States, this symbiosis saves around $4.5 billion in fertilizer costs and prevents ecological and health issues associated with the excessive use of chemical fertilizers. The rhizobium-legume symbiosis presents a high level of species specificity which means that specific legumes only associate with specific rhizobia. This specificity mechanism is mostly controlled by the structure of LCO (Lipo-Chito-Oligosaccharide) signals produced by the rhizobia and recognized by their host plants. LCOs also mediate associations with symbiotic fungi which occur in legumes but also in many other non-legume crops such as corn, wheat and cotton. LCOs are now used by farmers as plant growth promoters for legume and non-legume crops. Genetic analysis in plants allowed the identification of LCO receptors and proteins such as HMGR1 (3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase 1) that interact with LCO receptors and are required for the establishment of symbiotic associations. This project will lead to a better understanding of the mechanisms allowing legumes to recognize symbiotic LCOs and of the downstream pathways allowing LCO receptors and HMGR1 to mediate the development of root nodules with rhizobia and associations with symbiotic fungi. In the short term, understanding these mechanisms can have a direct impact on yield improvement through a more efficient use of LCOs as plant growth promoters. This knowledge will also help improve the establishment of plant-microbe associations, with especially high impact under suboptimal and stressful field conditions. In the long term, engineering new symbiotic associations through these mechanisms may help improve the sustainability of our agriculture for food, feed and biofuel production.