The Dual Role Of Phytoene Synthase Genes In Carrot

Carrot (Daucuscarota L.) is an important food crop and is useful for studying carotenogenesis due to the quantity and diversity of carotenoids in its storage roots. Phytoene synthase (PSY) catalyzes the first committed step in the carotenoid biosynthesis pathway, and its overexpression is the main driving force in the orange phenotype. Two PSY paralogs are present in carrot. But we lack fundamental knowledge of the role of these genes and their effects on carotenoid accumulation in leaves.In the present study, the backcross inbred lines (BILs; BC2S4) with different colored roots derived from a cross between the orange inbred line (Af) and related wild species (Ws) were used to clone the DNA and promoter sequences of DcPSYl and DcPSY2, to study the role of DcPSY1and DcPSY2in carrot roots and leaves, respectively.1. Conventional PCR was used to clone DNA sequences of DcPSY1and DcPSY2. The DNA sequence of DcPSY1was1972bp, DcPSY2was4015/4024bp. Multiple sequences alignment revealed that some SNPs existed in different carrot roots.2. Long and accurate (LA) PCR-based genomic walking was performed to clone DcPSY promoters and1.5kb long sequences were cloned. Promoter analysis showed that DcPSY promoter regions contain several potential cis-acting elements such as MYB binding site, ABA responsive elements (ABRE) and some light responsive elements.3. UPLC and real-time qPCR were used to analysis roles of the duplicated DcPSY genes in root carotenogenesis. It was demonstrated that expression levels of DcPSYl and DcPSY2were generally positively correlated with carotenoid content during root development.4. The effects of DcPSY expression on carotenoid accumulation in leaves were analyzed by UPLC and real-time qPCR. The results showed DcPSY1might play a preferential role in carotenoids accumulation in chloroplast, DcPSYl and DcPSY2expression levels were all regulated by light during leaf de-etiolation, and DcPSY1was more sensitive to light regulation. Meanwhile, the accumulation of a-carotene was found to be significantly different in different carrot leaves, the expression of DcPSY, DcLCYBl, DcLCYE, DcCHXBl and DcCHXE were negatively correlated with carotenoids content in leaves.