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Abstract：
Polyamines, such as putrescine, spermidine and spermine (Spm), are low-molecular-weight polycationic molecules present in all living organisms. Despite their implication in plant cellular processes, little is known about their molecular mode of action. Here, we demonstrate that polyamines trigger a rapid increase in the regulatory membrane lipid phosphatidylinositol 4,5-bisphosphate (PIP2 ), and that this increase is required for polyamine effects on K+ efflux in Arabidopsis roots. Using in vivo 32 Pi -labelling of Arabidopsis seedlings, low physiological (μm) concentrations of Spm were found to promote a rapid PIP2 increase in roots that was time- and dose-dependent. Confocal imaging of a genetically encoded PIP2 biosensor revealed that this increase was triggered at the plasma membrane. Differential 32 Pi -labelling suggested that the increase in PIP2 was generated through activation of phosphatidylinositol 4-phosphate 5-kinase (PIP5K) activity rather than inhibition of a phospholipase C or PIP2 5-phosphatase activity. Systematic analysis of transfer DNA insertion mutants identified PIP5K7 and PIP5K9 as the main candidates involved in the Spm-induced PIP2 response. Using non-invasive microelectrode ion flux estimation, we discovered that the Spm-triggered K+ efflux response was strongly reduced in pip5k7 pip5k9 seedlings. Together, our results provide biochemical and genetic evidence for a physiological role of PIP2 in polyamine-mediated signalling controlling K+ flux in plants.
摘要：
多胺,如腐胺，亚精胺和精胺（Spm），是存在于所有活生物体中的低分子量聚阳离子分子。尽管它们包含在植物细胞过程中，对它们的分子作用方式知之甚少。这里,我们证明多胺引发调节膜脂质磷脂酰肌醇4,5-二磷酸（PIP2）的快速增加，并且这种增加是多胺对拟南芥根中K外排的影响所必需的。使用拟南芥幼苗的体内32个Pi标记，发现Spm的低生理（μm）浓度可促进根中PIP2的快速增加，这是时间和剂量依赖性的。基因编码的PIP2生物传感器的共聚焦成像显示，这种增加是在质膜上触发的。差异32Pi标记表明，PIP2的增加是通过激活磷脂酰肌醇4-磷酸5-激酶（PIP5K）活性而不是抑制磷脂酶C或PIP25-磷酸酶活性而产生的。转移DNA插入突变体的系统分析将PIP5K7和PIP5K9鉴定为参与Spm诱导的PIP2应答的主要候选物。使用非侵入性微电极离子通量估计，我们发现Spm触发的K外排反应在pip5k7pip5k9幼苗中大大降低。一起,我们的结果为PIP2在多胺介导的信号控制植物K通量中的生理作用提供了生化和遗传证据。
