背景1：Copper (Cu) and iron (Fe) are essential micronutrients that are toxic when accumulating in excess in cells. Thus, their uptake by roots is tightly regulated. 

提出问题：While plants sense and respond to local Cu availability, the systemic regulation of Cu uptake has not been documented in contrast to local and systemic control of Fe uptake. 

背景2：Fe abundance in the phloem has been suggested to act systemically, regulating the expression of Fe uptake genes in roots. Consistently, shoot-to-root Fe signaling is disrupted in Arabidopsis thaliana mutants lacking the phloem companion cell-localized Fe transporter, OLIGOPEPTIDE TRANSPORTER 3 (AtOPT3). 

主要发现：We report that AtOPT3 also transports Cu in heterologous systems and contributes to its delivery from sources to sinks in planta. 

结果1-突变体库筛选：The opt3 mutant contained less Cu in the phloem, was sensitive to Cu deficiency and mounted a transcriptional Cu deficiency response in roots and young leaves. 

结果2-pdx1.1突变及拯救：Feeding the opt3 mutant and Cu- or Fe-deficient wild-type seedlings with Cu or Fe via the phloem in leaves downregulated the expression of both Cu and Fe-deficiency marker genes in roots. 

结论：These data suggest the existence of shoot-to-root Cu signaling, highlight the complexity of Cu/Fe interactions, and the role of AtOPT3 in fine-tuning root transcriptional responses to the plant Cu and Fe needs.

铜（Cu）和铁（Fe）是必要的微量营养元素，但在细胞中积累过量时会有毒害作用。因此，植物根对于铜和铁的吸收是受到紧密调控的。尽管植物能够感知并响应于局域的可利用铜，但是相比于铁吸收的局部和系统性控制，铜吸收的系统性调控研究还未见报道。韧皮部中的铁丰度被认为是系统性作用的，调控根中铁吸收基因的表达。与此一致的是，定位于拟南芥韧皮部伴细胞的铁转运蛋白AtOPT3的功能缺失，会导致拟南芥地上向地下的铁信号转导出现紊乱。作者发现AtOPT3在异源系统中还能够转运铜，并且在植物体内作用于铜从源到库的转运。opt3突变体的韧皮部铜含量更少，并且对于铜缺乏更加敏感，同时在根和嫩叶中存在铜缺乏的转录响应。对opt3突变体和铜或铁缺陷的野生型植株，通过叶片韧皮部提供铜或者铁，能够显著下调根中的铜和铁缺陷标记基因的表达。这些结果说明存在一个地上向地下的铜信号转导，表明了铜和铁互作的复杂性，同时也揭示了AtOPT3精细调控植物对铜和铁的转录响应。

** Olena K. Vatamaniuk **