背景回顾：Homeostasis of the essential micronutrient manganese (Mn) is crucially determined through availability and uptake efficiency in all organisms. Mn deficiency of plants especially occurs in alkaline and calcareous soils, seriously restricting crop yield. 

提出问题：However, the mechanisms underlying the sensing and signaling of Mn availability and conferring regulation of Mn uptake await elucidation. 

结果1-Mn缺乏与钙离子振荡：Here, we uncover that Mn depletion triggers spatiotemporally defined long-lasting Ca²⁺ oscillations in Arabidopsis roots. These Ca²⁺ signals initiate in individual cells, expand, and intensify intercellularly to transform into higher-order multicellular oscillations. 

结果1-CPK21/23-NRAMP1：Furthermore, through an interaction screen we identified the Ca²⁺-dependent protein kinases CPK21 and CPK23 as Ca²⁺ signal-decoding components that bring about translation of these signals into regulation of uptake activity of the high-affinity Mn transporter natural resistance associated macrophage proteins 1 (NRAMP1). 

结果2-CPK21/23功能：Accordingly, a cpk21/23 double mutant displays impaired growth and root development under Mn-limiting conditions, while kinase overexpression confers enhanced tolerance to low Mn supply to plants. 

结果3-NRAMP1磷酸化：In addition, we define Thr498 phosphorylation within NRAMP1 as a pivot mechanistically determining NRAMP1 activity, as revealed by biochemical assays and complementation of yeast Mn uptake and Arabidopsis nramp1 mutants.

结论：Collectively, these findings delineate the Ca²⁺-CPK21/23-NRAMP1 axis as key for mounting plant Mn homeostasis.

Model for LMn signaling and NRAMP Mn uptake regulation in Arabidopsis.

对于所有生物来说，通过可用性及吸收效率来维持必要微量元素锰（Mn）的体内稳态。生长在碱性或石灰性土壤中的植物往往会缺乏Mn，严重限制了作物产量。但是，可用Mn的感知和信号传导以及Mn吸收的调控机制均有待阐明。本文中，作者Mn缺乏会导致拟南芥根中持久的时空钙离子振荡。这些钙离子信号起始于单个细胞，在细胞间扩大、增强，最终转化为高阶的多细胞振荡。此外，作者鉴定到了两个钙离子依赖性激酶CPK21和CPK23作为钙离子信号解码组分，将这些钙离子信号翻译为Mn高亲和力转运蛋白NRAMP1的吸收活性调控。cpk21/23双突变体在Mn缺乏条件下表现出生长和根发育的缺陷，而这两个激酶的过表达则会表现出对Mn缺乏的耐受性增强。此外，作者通过对酵母Mn吸收和拟南芥nramp1突变体的生化试验和互补试验，发现NRAMP1蛋白498号位上苏氨酸的磷酸化是决定其活性的关键。综上，本文的研究结果揭示了Ca²⁺-CPK21/23-NRAMP1作用于植物Mn稳态的分子调控。

** 王 存 **