The dual role of phytoene synthase genes in carotenogenesis in carrot roots and leaves

Abstract

Carrot (<i>Daucus carota</i> L.) is an important food crop and is useful for studying carotenogenesis due to the quantity and diversity of carotenoids in its roots. Phytoene synthase catalyzes the first committed step in the carotenoid biosynthesis pathway, and its overexpression is the main driving force in the orange phenotype. At present, we lack fundamental knowledge of the role of these genes and their effects on carotenoid accumulation in leaves. In the present study, three backcross inbred lines (BC2S4) with different colored roots derived from a cross between the orange inbred line (Af) and related wild species were used to investigate the role of the duplicated <i>DcPSY</i> genes in root carotenogenesis. Promoter analysis showed that <i>DcPSY</i> genes have diverged substantially in their regulatory sequences after gene duplication. Expression levels of <i>DcPSY1</i> and <i>DcPSY2</i> were generally positively correlated with carotenoid content during root development. In mature leaves, total carotenoid content was higher than that in the roots, <i>DcPSY1</i> expression increased extremely higher than <i>DcPSY2</i> expression compared with roots, and <i>DcPSY1</i> was more sensitive than <i>DcPSY2</i> during leaf de-etiolation under sunlight. These results suggest that <i>DcPSY1</i> seems to make an important contribution to carotenoid accumulation in the leaves and is important for photosynthesis and photoprotection, but they are not the determining factors of root color. This expands our understanding of the regulation of carotenoid biosynthesis in carrot.