提出问题：This systemic N acquisition response is triggered by a root-to-shoot mobile peptide hormone, C-TERMINALLY ENCODED PEPTIDE (CEP), originating from the N-starved roots, but the molecular nature of the descending shoot-to-root signal remains elusive.

主要发现：Here, we show that phloem-specific polypeptides that are induced in leaves upon perception of root-derived CEP act as descending long-distance mobile signals translocated to each root.

试验结果：These shoot-derived polypeptides, which we named CEP DOWNSTREAM 1 (CEPD1) and CEPD2, upregulate the expression of the nitrate transporter gene NRT2.1 in roots specifically when nitrate is present in the rhizosphere. Arabidopsis plants deficient in this pathway show impaired systemic N acquisition response accompanied with N-deficiency symptoms.

结论：These fundamental mechanistic insights should provide a conceptual framework for understanding systemic nutrient acquisition responses in plants.

 摘  要 

植物主要通过硝酸盐的方式从土壤中吸收氮元素。然而，硝酸盐通常在天然土壤中分布不均匀。因此，植物具有系统性长距离信号传导机制，通过该机制，根一侧的氮饥饿会导致另一侧氮丰富区域的根部进行补偿性的氮吸收。该系统性的氮获取响应是通过一个root-to-shoot移动多肽激素CEP所介导的，CEP会在氮饥饿一侧的根组织中产生，但是由shoot-to-root的递降信号还不清楚是什么。本文中，作者发现了韧皮部特异性多肽会在感知到来自于根的CEP后，在叶片组织中被诱导，而后作为一个递降的长距离移动信号被转运到每一个根中。这些来自于地上组织的多肽被叫做为CEPD1和CEPD2，这些蛋白能够在根际土壤中存在硝酸盐时，特异性上调根中的硝酸盐转运基因NRT2.1的表达。改通路突变了的拟南芥植株会显示出系统性氮获取响应的缺陷，同时伴随着氮缺乏症状。本文的研究为植物中系统性营养元素获取响应提供了一个概念性框架。