Identification of 1,6-hexadecanediol and its wax diesters in chloroplasts of Nicotiana benthamiana.

Main conclusion: Expression of the Arabidopsis phytyl ester synthase PES2 in Nicotiana benthamiana chloroplasts resulted in the accumulation of fatty acid phytyl esters and wax diesters containing the novel alkanediol 1,6-hexadecanediol. Dihydric long-chain alcohols carrying two hydroxyl groups are low abundant in plants and are mostly found in the cutin layer of leaves or the suberin of roots. Transient expression of the phytyl ester synthase PES2 from Arabidopsis thaliana in Nicotiana benthamiana resulted in the accumulation of fatty acid phytyl esters (FAPEs) and of a new lipid class that was identified as wax diesters of 1,6-hexadecanediol, carrying mostly lauric acid (12:0) and myristic acid (14:0) residues. The synthesis of FAPE and wax diesters was only observed when PES2 was targeted to the chloroplasts, in agreement with the finding that both FAPE and wax diesters are chloroplast-localized. The accumulation of wax diesters following PES2 expression demonstrates that the dihydric long-chain alcohol, 1,6-hexadecanediol, is an authentic compound produced in N. benthamiana chloroplasts. 1,6-Hexadecanediol in N. benthamiana is likely synthesized by a chloroplast-localized fatty acid reductase (FAR) in combination with a P450 monooxygenase. PES2-mediated acylation might result in chloroplast-trapping of 1,6-hexadecanediol which is possibly an intermediate in the biosynthesis of functional compounds in leaves or other plant organs.