Abstract：
Plants use a combination of sophisticated local and systemic pathways to optimize growth depending on heterogeneous nutrient availability in the soil. Legume plants can acquire mineral nitrogen (N) either through their roots or via a symbiotic interaction with N-fixing rhizobia bacteria housed in so-called root nodules. To identify shoot-to-root systemic signals acting in Medicago truncatula plants at N-deficit or N-satiety, plants were grown in a split-root experimental design, in which either high or low N was provided to a half of the root system, allowing the analysis of systemic pathways independently of any local N response. Among the plant hormone families analyzed, the cytokinin trans-Zeatin accumulated in plants at N-satiety. Cytokinin application by petiole feeding led to an inhibition of both root growth and nodulation. In addition, an exhaustive analysis of miRNAs revealed that miR2111 accumulates systemically under N-deficit in both shoots and non-treated distant roots, whereas a miRNA related to inorganic Phosphate (Pi)-acquisition, the miR399, does so in plants grown at N-satiety. These two accumulation patterns are dependent on CRA2 (Compact Root Architecture 2), a receptor required for CEP (C-terminally Encoded Peptide) signaling. Constitutive ectopic expression of the miR399 reduced nodule numbers and root biomass depending on Pi availability, suggesting that the miR399-dependent Pi-acquisition regulatory module controlled by N-availability affects the development of the whole legume plant root system.
摘要：
植物使用复杂的局部和系统途径的组合来优化生长，这取决于土壤中的异质养分利用率。豆科植物可以通过其根部或通过与所谓的根瘤中的固氮根瘤菌的共生相互作用获得矿质氮（N）。为了确定在N缺乏或N饱腹感下在苜蓿植物中作用的芽到根的系统信号，植物在分根实验设计中生长，其中高氮或低氮被提供给一半的根系，允许独立于任何局部N反应的系统途径分析。在分析的植物激素家族中，N-饱腹感在植物中积累的细胞分裂素反式玉米素。通过叶柄喂养施用细胞分裂素导致根生长和结瘤的抑制。此外,对miRNAs的详尽分析显示，miR2111在芽和未处理的远缘根中的氮缺乏下系统积累，而与无机磷酸盐（Pi）获取相关的miRNA，miR399，在生长在饱腹感的植物中这样做。这两种累积模式依赖于CRA2(紧凑根架构2)，CEP（C端编码肽）信号传导所需的受体。根据Pi的可用性，miR399的组成型异位表达减少了结节数量和根生物量，表明由N可用性控制的依赖miR399的Pi获取调节模块会影响整个豆科植物根系的发育。
