2-Hydroxy-phytanoyl-CoA lyase (AtHPCL) is involved in phytol metabolism in Arabidopsis.

During chlorophyll degradation, large amounts of the isoprenoid alcohol phytol are released. The pathway of phytol catabolism has been studied in humans, because chlorophyll is part of the human diet, but little is known for plants. In humans, phytanoyl-CoA derived from phytol is degraded via α-oxidation by phytanoyl-CoA hydroxylase (PAHX) and 2-hydroxy-phytanoyl-CoA lyase (HPCL). Arabidopsis contains two sequences homologous to the human proteins AtPAHX and AtHPCL. Insertional mutants of Arabidopsis (pahx, hpcl) were grown under N deprivation to stimulate chlorophyll breakdown or supplemented with phytol to increase the endogenous amount of phytol. During N deprivation, chlorophyll, phytol, phytenal, upstream metabolites of phytol breakdown, and tocopherol and fatty acid phytyl esters, alternative phytol-derived lipids, accumulated in pahx and hpcl mutants, in line with the scenario that the mutations interfere with phytol degradation. AtHPCL was localized to the peroxisomes. Expression analysis of the AtHPCL sequence in the yeast Δpxp1 or Δmpo1 mutants followed by supplementation with 2-hydroxy-palmitic acid and enzyme assays of peroxisomal proteins from Col-0 and hpcl plants with 2-hydroxy-stearoyl-CoA revealed that AtHPCL harbors 2-hydroxy-acyl-CoA lyase activity. The α-dioxygenases αDOX1 and αDOX2 are involved in α-oxidation of fatty acids and could be involved in an alternative pathway of phytol degradation. However, phytol-related lipids in the αdox1, αdox2, or αdox1 αdox2 mutants were not altered compared with Col-0, indicating that αDOX1 and αDOX2 are not involved in phytol degradation. These results demonstrate that phytol degradation in Arabidopsis involves α-oxidation by AtPAHX and AtHPCL, but that it is independent of αDOX1/αDOX2.

Fatty acid isoprenoid alcohol ester synthesis in fruits of the African Oil Palm (Elaeis guineensis).

The African Oil Palm (Elaeis guineensis; family Arecaceae) represents the most important oil crop for food and feed production and for biotechnological applications. Two types of oil can be extracted from palm fruits, the mesocarp oil which is rich in palmitic acid and in carotenoids (provitamin A) and tocochromanols (vitamin E), and the kernel oil with high amounts of lauric and myristic acid. We identified fatty acid phytyl esters (FAPEs) in the mesocarp and kernel tissues of mature fruits, mostly esterified with oleic acid and very long chain fatty acids. In addition, fatty acid geranylgeranyl esters (FAGGEs) accumulated in mesocarp and kernels to even larger amounts. In contrast, FAPEs and FAGGEs amounts and fatty acid composition in leaves were very similar. Analysis of wild accessions of African Oil Palm from Cameroon revealed a considerable variation in the amounts and composition of FAPEs and FAGGEs in mesocarp and kernel tissues. Exogenous supplementation of phytol or geranylgeraniol to mesocarp slices resulted in the incorporation of these alcohols into FAPEs and FAGGEs, respectively, indicating that they are synthesized via enzymatic reactions. Three candidate genes of the esterase/lipase/thioesterase (ELT) family were identified in the Oil Palm genome. The genes are differentially expressed in mesocarp tissue with EgELT1 showing the highest expression. Geranylgeraniol from FAGGE might be recycled and used as a substrate for the synthesis of carotenoids and tocotrienols during fruit development. Thus, FAPEs and FAGGEs in the mesocarp and kernel of Oil Palm provide an additional metabolic source for fatty acids and phytol or geranylgeraniol, respectively.