The Four Arabidopsis Choline/Ethanolamine Kinase Isozymes Play Distinct Roles in Metabolism and Development

Abstract

Phosphatidylcholine and phosphatidylethanolamine are 2 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 4 CEK isoforms but their isozyme-specific roles in metabolism and development are poorly described. Here, we showed that these 4 CEKs have distinct substrate specificities in vitro. While CEK1 and CEK2 showed substrate preference for choline over ethanolamine, CEK3 and CEK4 had a clear substrate specificity for choline or ethanolamine, respectively. In vivo, CEK1, CEK2, and CEK3 exhibited kinase activity for choline but not ethanolamine, although the latter 2 isoforms showed rather minor contributions to total choline kinase activity in both shoots and roots. The knockout mutants of CEK2 and CEK3 both affected root growth, and these isoforms had non-overlapping 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 choline-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 4 CEK isoforms in choline/ethanolamine metabolism and plant development.

The Delay of Raphanus raphanistrum subsp. sativus (L.) Domin Seed Germination Induced by Coumarin Is Mediated by a Lower Ability to Sustain the Energetic Metabolism

“…In conclusion, the specific effect of coumarin on Ca 2+ reabsorption, which was not observed for K + , could represent a crucial point in its inhibitory action. Phosphocoline is an intermediate in phospholipids’ biosynthesis that is related to membrane biosynthesis, a crucial event in seed germination [ 35 , 36 ]. In the present study, phosphocholine, with production that is strictly dependent on ATP, was significantly lower after 24 h of treatments (in agreement with the lower ATP level observed) but was restored to the control level after 48 h. These data strongly support the hypothesis that during the first 24 h of treatment, coumarin could delay membrane synthesis and organisation.…”

At4g29530 is a phosphoethanolamine phosphatase homologous to PECP1 with a role in flowering time regulation

“…Recent studies with T‐DNA knockout lines and overexpression lines revealed that only CEK4 functions as an Etn kinase (Lin et al. , 2020). In contrast to PMT1, which is feedback inhibited by PCho (BeGora et al.…”

“…In A. thaliana, four homologous CEKs were identified (Lin , 2015). Recent studies with T-DNA knockout lines and overexpression lines revealed that only CEK4 functions as an Etn kinase (Lin et al, 2020). In contrast to PMT1, which is feedback inhibited by PCho (BeGora et al, 2010), it is not known whether CEK4 is under metabolic control, for example, inhibited by its product, PEtn.…”

Choline Kinase: An Unexpected Journey for a Precision Medicine Strategy in Human Diseases

“…Furthermore, phosphatidylethanolamine (PE) levels are unaffected in ChoKβ KO mice, a result which suggests that PE homeostasis is fully maintained when the ChoKα protein is intact [9]. Again, in Arabidopsis, substrate specificity for Cho and Etn are distinct for the four CEK enzymes [14] and resembles the situation described in mammalian cells [15].…”

“…In humans, mutations in the CHKB gene lead to similar pathology [13]. Finally, in Arabidopsis, there are four Choline-Ethanolamine Kinase (CEK) genes related to choline (Cho) and ethanolamine (Etn) phosphorylation, with different roles in metabolism and development [14].…”