王存等《Molecular Plant》2021年

论文题目：A Tonoplast-associated Calcium Signaling Regulates Manganese Homeostasis in Arabidopsis

论文作者：Zhenqian Zhang1#, Dali Fu1#, Zhihui Sun2#, Chuanfeng Ju1, Cuicui Miao1, Zhangqing Wang1, Dixiang Xie1, Liang Ma2, Zhizhong Gong2, 3 and Cun Wang1*.

Ca2+是真核细胞内广泛存在的第二信使，在植物响应逆境胁迫和生长发育的过程中扮演着重要角色。然而，Ca2+信号是否参与调控锰信号转导途径？如果参与，其具体的分子机制是什么？这一科学问题至今悬而未决。研究人员通过Aequorin报告基因以及Fluo-4染色方法，首次明确了高锰胁迫能够诱导产生Ca2+信号。基于此，研究人员进一步研究了钙信号在高锰胁迫中的作用和分子机制。通过系统筛选发现，钙依赖蛋白激酶CPKs家族中的CPK4/5/6/11与定位于液泡膜的锰转运体MTP8物理互作。利用多种蛋白互作技术证明了CPK4/5/6/11与MTP8互作的真实性。最后，通过体内体外磷酸化、酵母功能互补、元素含量测定以及生理表型等实验发现，CPK4/5/6/11通过磷酸化MTP8的第31位和32位丝氨酸激活其转运活性，进而将细胞质中的多余锰离子转运进液泡内，提高植物耐受锰毒害的能力。此外，模拟磷酸化状态的MTP8还能提高植物在低锰胁迫条件下的种子萌发和幼苗生长。

论文摘要：Manganese (Mn) is an essential micronutrient in plants. However, excessive Mn absorption in acidic and waterlogged soils can lead to Mn toxicity. Despite their essential roles in Mn homeostasis, the transcriptional and post-transcriptional modification of Mn transporters remain poorly understood. Here, we demonstrated that high Mn stress induces an obvious Ca2+ signature in Arabidopsis. We identified four calcium-dependent protein kinases, CPK4/5/6/11, interacting with the tonoplast-localized Mn and iron (Fe) transporter MTP8 in vitro and in vivo. The cpk4/5/6/11 quadruple mutant displayed a dramatic high Mn sensitive phenotype similar to that of the mtp8 mutant. CPKs phosphorylated the N-terminal domain of MTP8 primarily at Ser31 and Ser32 residues. Transport assays combined with multiple physiology experiments on phospho-dead variant MTP8S31/32A and phospho-mimetic variant MTP8S31/32D plants under different Mn and Fe conditions suggested Ser31 and Ser32 are crucial for MTP8 function. In addition, genetic analysis showed that CPKs functioned upstream of MTP8. In summary, we identified a tonoplast-associated calcium signaling cascade, which orchestrates Mn homeostasis and links Mn toxicity, Ca2+ signaling and Mn transporters. These findings provide new insight into Mn homeostasis mechanisms and Ca2+ signaling pathways in plants and should be useful in promoting the breeding of heavy metal toxicity-tolerant plants.  

论文链接：https://www.cell.com/molecular-plant/fulltext/S1674-2052(21)00078-2