Understanding the regulations of vitamin E biosynthesis in tomato fruits

QUADRANA L; ASÍS R; OTAIZA S; OSORIO S; FERNIE AR; ALMEIDA J, QUADRANA L, ASIS R, SETTA N, DE GODOY F, BERMÚDEZ L, OTAIZA SN, CORRÊA DA SILVA JV, FERNIE AR, CARRARI F AND ROSSI M; CARRARI F

West Kingston

Conferencia; Plant Metabolic Engineering; 2011

Understanding of metabolic pathways regulation in plants is of fundamental importance especially for the biosynthesis of essential compounds for human diets. Although tomato fruits are important sources of vitamin E neither the genetic determinants of its contents nor the regulation of its biosynthesis are currently understood in this species. We present here results from the analyses of QTL for tocopherol contents in mature fruits previously identified in an introgression line (IL) population derived from an interspecific cross harboring wild alleles. Fine mapping of two of these QTL allowed to identify three vte loci (vte1, vte3 and vte4) encoding enzymes of the last steps in vitamin E synthesis in plants. Expression profiles of these genes showed their expression pattern in source and sink leaves and also across fruit development. Fruit silencing of vte4 gene resulted in reduced levels of α- and -tocopherol and a consequent accumulation of -tocopherol both in mature green and ripe tomatoes. By other hand, the reduction of the vte3 mRNA resulted in significant increases of -tocopherol both at mature green and ripe stages. However, at this later stage -tocopherol levels resulted also significantly reduced. Vte1 gene was not sensitive to silencing by this system. These results suggest that other unknown mechanism could be operating in the regulation of this enzymatic step catalyzed by VTE1 and also that a different regulatory role of VTE3 enzyme exists with regards to the maturation stage of the fruits. Moreover, detailed metabolite profiles of silenced fruits showed that alterations in tocopherol levels correlated with massive increases in the concentrations of the photorespiratory intermediate glycine (~ 4 folds) and the levels of leucine (~ 3 folds) in ripe fruits. These changes were accompanied by increments in the levels of the pigments carotenes and lycopene, suggesting that both tocopherol and carotenoid pathways are co-regulated. Moreover, vte4 silencing was accompanied by increments in antioxidant capacity in green and ripe tomatoes, while the silencing of vte3 resulted in increased antioxidant levels in ripe fruits. These results suggest that tocopherol composition may regulate the pigment accumulation and the cellular redox state of the tomato fruits.