Gene Expression and Genetic Analysis of Carotenoid Pigment Accumulation in Carrot (Daucus Carota L.)

Download or read book Gene Expression and Genetic Analysis of Carotenoid Pigment Accumulation in Carrot (Daucus Carota L.) written by and published by . This book was released on 2012 with total page 510 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carrot (Daucus carota) is an important vegetable crop, providing over 30% of the pro-vitamin A carotenoids in the human diet in the United States. As a major source of these nutriceutical compounds, research efforts have been directed to the regulation of this complex metabolic pathway. This project focused on evaluating gene expression, sequence changes and genetic mapping as it relates to the accumulation of the carotenoid pigments alpha-carotene, beta-carotene, xanthophylls, and lutein. Real-time quantitative PCR (RT-qPCR) was used to determine the level of expression of genes in the carotenoid biosynthesis pathway in different carrot culitvars. Two genes, phytoene synthase 1 (PSY1) and phytoene synthase 2 (PSY2) were found to be expressed at significantly higher levels in orange and dark orange carrot cultivars, whereas the pale orange rp "reduced pigment" mutant exhibited reduced phytoene desaturase (PDS) expression. DNA sequence analysis of putative promoter and coding regions of both PSY1 and PSY2 has identified sequence polymorphisms and large deletions were identified in the putative promoter of PSY2 in the dark orange cultivar B2327. Simple sequence repeat markers (SSRs) were used to create a genetic map from an F2 population segregating for the rp mutation. HPLC (high performance liquid chromatography) analyses of the carotenoids of carrot leaf tissue demonstrated xanthophylls and beta-carotene as the carotenoids present in all carrots, but significantly higher levels of alpha-carotene was identified in carrot germplasm with orange and dark orange storage roots. Chlorophyll fluorescence analysis identified genotype specific variation in photosystem II efficiency, significantly impacted by the time of harvest. To identify new candidate genes involved in carotenoid accumulation in carrot storage root, microarray analysis of sibling white and orange inbred lines from a cross of orange X white carrots was completed. Expression of three genes involved in photosynthesis was significantly higher in the orange rooted carrot germplasm. To examine the role that chromoplast biosynthesis may have in the accumulation of carotenoid pigments, the ratio of nuclear to plastid genome was analyzed in carrot germplasm with differing levels of pigmentation.