[Yuki Nakamura] An essential role of seemingly non-essential enzyme family.

Choline is an essential nutrient from food uptake for animals and its deficiency affects nerve transmission and cellular membrane integrity, causing serious diseases. As plants do not eat, choline acquisition will not happen and thus choline would not be an essential nutrient for plants. However, Arabidopsis has 4 copies of choline kinases and one of them is essential for plant viability. Why essential for metabolizing seemingly non-essential nutrient? We found that this kinase actually functions not as a choline kinase but ethanolamine kinase, catalyzing a crucial step in de novo phospholipid biosynthesis. Our phylogenetic analysis suggests that this may be a common feature at least in Brassicaceae. Thus, a homologous enzyme might have evolved to take a different substrate and catalyze an alternative essential metabolic reaction.