Arabidopsis phytyl ester synthases PES1 and PES2 moonlighted as xanthophyll acyltransferases in plants.

Main conclusion: Proteins coded by At1g54570 and At3g25840 previously characterized in the synthesis of phytyl acyl esters also catalyze xanthophyll acyl esterification under tissue-culture-induced stress and when expressed in transgenic tomato. Fatty acyl esters of xanthophylls accumulate in flower petals and ripening fruit of many plant taxa. The genes involved in xanthophyll esterification are, therefore, of interest as xanthophyll esters are known in determining flower and fruit coloration and the accumulation and stability of nutritionally valuable carotenoids. Arabidopsis thaliana proteins homologous to tomato xanthophyll acyltransferases PYP1 and PYP1-like coded by At1g54570 (AtPES1) and At3g26840 (AtPES2), respectively, were previously implicated in the synthesis of fatty acid phytyl esters and triacylglycerol. Here, we tested the hypothesis that AtPES1 and AtPES2 proteins could have roles in xanthophyll esterification also. Chromatographic analyses quantifying carotenoids from tissue-cultured callus of WT, pes1, pes2, and the double mutant pes1/pes2 revealed that AtPES1 and AtPES2 have overlapping functions in the synthesis of xanthophyll mono-, di-, and tri-esters. The xanthophyll esters from Arabidopsis callus were further confirmed and identified by LC-MS. Given AtPES1 and AtPES2's homology to PYP1 and PYP1-like in tomato, complementation tests were performed in the tomato mutant, pyp1-1(H7L) impaired for xanthophyll esterification, in which AtPES1 and AtPES2 were overexpressed. Transgenic expression of PES1 restored the dull yellow petal phenotype of pyp1-1(H7L) to bright yellow like that of the wild-type and xanthophyll esters could be identified in their petal extracts. Transgenic expression of AtPES2 had similar, but less effective impact on restoring petal coloration and xanthophyll ester profiles than AtPES1. Together, our results indicate that Arabidopsis AtPES1 and AtPES2 proteins have overlapping functions in the synthesis of xanthophyll acyl esters.