Levels of Lycopene b-Cyclase 1 Modulate Carotenoid Gene Expression and Accumulation in Daucus carota

Abstract

Plant carotenoids are synthesized and accumulated in plastids through a highly regulated pathway. Lycopene b-cyclase (LCYB) is a key enzyme involved directly in the synthesis of a-carotene and b-carotene through the cyclization of lycopene. Carotenoids are produced in both carrot (Daucus carota) leaves and reserve roots, and high amounts of a-carotene and bcarotene accumulate in the latter. In some plant models, the presence of different isoforms of carotenogenic genes is associated with an organ-specific function. D. carota harbors two Lcyb genes, of which DcLcyb1 is expressed in leaves and storage roots during carrot development, correlating with an increase in carotenoid levels. In this work, we show that DcLCYB1 is localized in the plastid and that it is a functional enzyme, as demonstrated by heterologous complementation in Escherichia coli and over expression and post transcriptional gene silencing in carrot. Transgenic plants with higher or reduced levels of DcLcyb1 had incremented or reduced levels of chlorophyll, total carotenoids and b-carotene in leaves and in the storage roots, respectively. In addition, changes in the expression of DcLcyb1 are accompanied by a modulation in the expression of key endogenous carotenogenic genes. Our results indicate that DcLcyb1 does not possess an organ specific function and modulate carotenoid gene expression and accumulation in carrot leaves and storage roots.