The mechanism of a shoot-induced regulation of N2-fixation in soybean

该提案的一个主要目标是将在模式豆科植物紫花苜蓿上获得的成果转移到经济上重要的作物大豆上。短叶紫花苜蓿的固氮调控显然是由茎部诱导的，并依赖于茎部的氮状态。一些环境和营养因素诱导了一个一致的、有节奏的N2固定时间过程，这减少了每天的固定氮量。在这些不同的因素中，铵的施用或在超结突变体中形成大量的根瘤。在项目开始时，将确定施用铵后或大豆芽变黑后氮固定的精确时间过程。基于茎部诱导的根瘤效应与miRNA有关的假设，随后将在根瘤节律性n2固定期间精确确定的时间点进行全面的比较mRNA和miRNA转录组分析（RNAseq）。下一步，在诱导观察到的有节奏的N2固定的各种因素的影响下，通过qPCR跟踪确定的候选基因在24小时内的表达。在这些因素中，豆荚形成的影响或突变体中异常大量的结节是结瘤自动调节缺陷的影响。这一结果将为可能的努力提供一个先决条件，即生产出不依赖土壤中铵浓度的氮固定的大豆，并可能在超结瘤状态下更有效地固定氮。这两个因素对大豆产量都有重要影响。

A main objective of the proposal is to transfer results obtained on the model legume Medicago truncatula to the economically important crop soybean. The regulation of N2 fixation in Medicago truncatula is clearly shoot-induced and dependent on the N-status of the shoot. Several environmental and nutritional factors induce a consistent, rhythmic time-course of N2 fixation, that decreases the per day amount of fixed nitrogen. Among these diverse factors is the application of ammonium to the roots or the formation of a high number of nodules in supernodulating mutants. The precise time-course of N2-fixation after ammonium application or darkening of the shoots of soybean will be ascertained in the beginning of the project. Based on the hypotheses that the shoot induced effect on nodules is related to miRNA, a comprehensive comparative mRNA and miRNA transcriptome profiling (RNAseq) will subsequently be performed at precisely defined point in time during the rhythmic N2-fixation of the nodules. As a next step, identified candidates will be followed in their expression by qPCR under the influence of various factors that induce the observed rhythmic N2 fixation over a 24 h period. Among these factors is the influence of pod-formation or that of an unusual large number of nodules in a mutant that is defect in the autoregulation of nodulation. The results will be a prerequisite for a possible effort to produce soybean that is independent in its N2 fixation of the ammonium concentration in the soil and might fix nitrogen more efficiently in a state of supernodulation. Both factors could be of significant importance for the productivity of soybean.