Phosphatidylcholine and phosphatidylethanolamine are two major phospholipid classes in eukaryotes. Each biosynthesis pathway starts with the phosphorylation of choline (Cho) or ethanolamine (Etn) catalyzed by either choline or ethanolamine kinase (CEK). Arabidopsis contains four CEK isoforms, but their isozyme-specific roles in metabolism and development are poorly described. Here, we showed that these four CEKs have distinct substrate specificities in vitro. While CEK1 and CEK2 showed substrate preference for Cho over Etn, CEK3 and CEK4 had clear substrate specificity for Cho and Etn, respectively. In vivo, CEK1, CEK2, and CEK3 exhibited kinase activity for Cho but not Etn, although the latter two isoforms showed rather minor contributions to total Cho kinase activity in both shoots and roots. The knockout mutants of CEK2 and CEK3 both affected root growth, and these isoforms had nonoverlapping cell-type-specific expression patterns in the root meristematic zone. In-depth phenotype analysis, as well as chemical and genetic complementation, revealed that CEK3, a Cho-specific kinase, is involved in cell elongation during root development. Phylogenetic analysis of CEK orthologs in Brassicaceae species showed evolutionary divergence between Etn kinases and Cho kinases. Collectively, our results demonstrate the distinct roles of the four CEK isoforms in Cho/Etn metabolism and plant development.

中文翻译：

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四种拟南芥胆碱/乙醇胺激酶同工酶在代谢和发育中起着不同的作用。

磷脂酰胆碱和磷脂酰乙醇胺是真核生物中的两个主要磷脂类别。每个生物合成途径均以胆碱或乙醇胺激酶（CEK）催化胆碱（Cho）或乙醇胺（Etn）的磷酸化开始。拟南芥含有四种CEK同工型，但它们在代谢和发育中同工酶特异的作用描述不多。在这里，我们表明这四个CEKs在体外具有不同的底物特异性。虽然CEK1和CEK2对Cho的底物优先于Etn，但CEK3和CEK4分别对Cho和Etn的底物具有明确的特异性。在体内，CEK1，CEK2和CEK3对Cho表现出激酶活性，但对Etn没有表现，尽管后两种同工型对芽和根中的总Cho激酶活性表现出较小的贡献。CEK2和CEK3的敲除突变体都影响根的生长，并且这些同工型在根分生组织区具有不重叠的细胞类型特异性表达模式。深入的表型分析以及化学和遗传互补研究表明，CEK特异性激酶CEK3与根发育过程中的细胞伸长有关。对十字花科植物中的CEK直系同源基因进行系统进化分析表明Etn激酶和Cho激酶之间存在进化差异。总的来说，我们的结果证明了四种CEK亚型在Cho / Etn代谢和植物发育中的独特作用。参与根发育过程中的细胞伸长。十字花科植物对CEK直系同源物的系统进化分析表明，Etn激酶和Cho激酶之间存在进化差异。总的来说，我们的结果证明了四种CEK亚型在Cho / Etn代谢和植物发育中的独特作用。参与根发育过程中的细胞伸长。对十字花科植物中的CEK直系同源基因进行系统进化分析表明Etn激酶和Cho激酶之间存在进化差异。总的来说，我们的结果证明了四种CEK亚型在Cho / Etn代谢和植物发育中的独特作用。