Ammonium sensing by plant roots

植物根系对土壤中局部营养斑块的感知不仅是提高植物在自然生境中的竞争力策略的一部分，而且在农业生产系统中对提高作物的肥料利用效率也很重要。由于侧根对某些营养物质的局部供应具有高度的响应性，侧根的形成被认为是一种营养感知的形态学读出。在第一个资助期，我们已经表明，局部铵供应触发高阶侧根分支，而硝酸盐刺激侧根伸长。2 .在拟南芥中，这种形态反应是由铵转运体AMT1介导的；本提案的目的是i)调查AMT1；3作为铵受体，将铵转运过程与导致侧根分支的信号事件耦合；Ii)确定植物激素生长素在氨诱导侧根分支中的作用，iii)从转录组方法中鉴定出的一组基因中鉴定出铵转运过程下游的铵信号通路中的基因。我们的方法包括AMT启动子交换实验，在四组AMT敲除系（qko）中进行表达，并在具有局部铵供应的分裂琼脂板上进行根系分析。此外，重组AMTs表达的qko系将被生长素报告基因构建体转化，并分析候选基因的表达。最终目标是鉴定拟南芥根系中的分子成分，将局部受限铵源信息整合到根系发育计划中。

The sensing of localized nutrient patches in soils by plant roots is not only part of a strategy to increase the competitiveness of plants in natural habitats but also important in agricultural production systems to improve fertilizer use efficiency of crops. Due to the high responsiveness of lateral roots to the localized supply of certain nutrients, lateral root formation has been established as a morphological read-out for nutrient sensing. During the first funding period, we have shown that localized ammonium supply triggers higher-order lateral root branching whereas nitrate stimulates lateral root elongation. In Arabidopsis, this morphological response is mediated by the ammonium transporter AMT1;3. The aim of the present proposal is i) to investigate whether AMT1;3 acts as an ammonium transceptor coupling the ammonium transport process with a signaling event leading to lateral root branching; ii) to determine the role of the phytohormone auxin in ammonium-induced lateral root branching, and iii) to identify genes in the ammonium signaling pathway downstream of the ammonium transport process from a set of genes identified in transcriptome approaches. Our approach includes AMT promoter swapping experiments for expression in a quadrouple amt knock-out line (qko) and root system analysis on split-agar plates with localized ammonium supplies. Moreover, qko lines with reconstituted expression of individual AMTs will be transformed with auxin reporter constructs and analyzed for expression of candidate genes. The ultimate goal is to identify molecular components in Arabidopsis roots integrating the information on a locally restricted ammonium source into the root developmental program.