Defects in CTP:PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE Affect Embryonic and Postembryonic Development in Arabidopsis

Abstract

A TILLING strategy (for targeting-induced local-scale lesions in genomes) was used in Arabidopsis thaliana to isolate mutants of a gene encoding CTP:PHOSPHORYLETHANOLAMINE CYTIDYLYLTRANSFERASE (PECT; EC 2.7.7.14), a ratelimiting enzyme in phosphatidylethanolamine biosynthesis. A null mutation, pect1-6, caused embryo abortion before the octant stage. However, reciprocal crosses revealed that pect1-6 caused no significant gametophytic defect. In pect1-4, PECT activity was decreased by 74%. Growth was generally normal in these mutants, despite delays in embryo maturation and reduced fertility. At low temperatures, however, homozygotic pect1-4 plants displayed dwarfism. PECT activity was decreased by 47% in heterozygotic pect1-6 plants and by 80% in pect1-4/pect1-6 F1 plants, which also displayed a small but significant decrease of phosphatidylethanolamine and a reciprocal increase in phosphatidylcholine. These lipid changes were fully reversed by wild-type PECT1 expression. pect1-4/pect1-6 F1 plants displayed severe dwarfism, tissue abnormalities, and low fertility, which was attributable in part to inhibition of anther, embryo, and ovule development, as was the reduced fertility of pect1-4 seedlings. PECT1 cDNA expression under the control of an inducible promoter partially rectified the mutant phenotypes observed in pect1-4/pect1-6 F1 seedlings, indicating that malfunctions in different tissues have a synergistic effect on the mutant phenotypes.

The Choline/Ethanolamine Kinase Family in Arabidopsis: Essential Role of CEK4 in Phospholipid Biosynthesis and Embryo Development

“…These observations suggest that CEK4 function may be critical during embryo development. The embryo lethality of cek4-1/+ may be due to a deficiency in phospholipid biosynthesis because mutation in PECT, which catalyzes the reaction following CEK, affects PtdEtn biosynthesis and results in an embryo-lethal phenotype (Mizoi et al, 2006). Moreover, a null mutation in SDC may be lethal (Kwon et al, 2012).…”

“…Therefore, the initial pathway from Ser to P-Etn appears to be the gateway that channels amino acid metabolism into phospholipid biosynthesis and, hence, the rate-limiting step in PtdCho and PtdEtn biosynthesis. In Arabidopsis, knocking out of PECT1 causes embryonic lethality, and knocking down of PECT1 increases PtdCho levels at the expense of PtdEtn levels (Mizoi et al, 2006;Nakamura et al, 2014b). In addition, knocking out of PMT1 (or PEAMT1, XPL1) reduces PtdCho levels slightly (CruzRamírez et al, 2004).…”

“…P-Etn is a common substrate for the biosynthesis of both PtdEtn and PtdCho: PtdEtn is produced via cytidine diphosphoethanolamine by CTP:phosphorylethanolamine cytidylyltransferase (PECT) (Mizoi et al, 2006) and amino alcohol:aminophosphotransferase (Dewey et al, 1994), whereas PtdCho synthesis requires trimethylation of P-Etn to P-Cho catalyzed by S-adenosyl-L-methionine: phosphoethanolamine N-methyltransferase (PMT) (Bolognese and McGraw, 2000). P-Cho is converted by CTP:phosphorylcholine cytidylyltransferase to cytidine diphospho-choline (Inatsugi et al, 2002), which is then incorporated into the DAG backbone by amino alcohol:aminophosphotransferase to produce PtdCho.…”

The Kennedy pathway—De novo synthesis of phosphatidylethanolamine and phosphatidylcholine

“…It has been suggested that ECT physically interacts with EPT, as a way of channeling CDP-ethanolamine to the final step of the Kennedy pathway (59). ECT appears to localize primarily to the mitochondria in plants (56). In C. reinhardtii, there is no cytosolic activity, instead the ECT is predicted to have multiple transmembrane domains with a C-terminal signal sequence (amino acids 379-382) that appears to serve as a subcellular targetting sequence to the ER (Fig.…”

Oil-Body-Membrane Proteins and Their Physiological Functions in Plants

“…31) These stresses damage membrane of plant cells. 32,33) Freezing stress may cause undetectable damage to oleosindeficient membrane of oil bodies, which causes oil bodies to fuse additionally. The additionally enlarged oil bodies of ole1 seeds are similar to oil bodies of ole1 ole2 seeds.…”