| Abstract: | ABSTRACT: BACKGROUND: Carotenoids are a heterogeneous group of plant isoprenoids primarily involved inphotosynthesis. In plants the cleavage of carotenoids leads to the formation of thephytohormones abscisic acid and strigolactone, and C13-norisoprenoids involved in thecharacteristic flavour and aroma compounds in flowers and fruits and are of specificimportance in the varietal character of grapes and wine. This work extends the previousreports of carotenoid gene expression and photosynthetic pigment analysis by providing anup-to-date pathway analysis and an important framework for the analysis of carotenoidmetabolic pathways in grapevine. RESULTS: Comparative genomics was used to identify 42 genes putatively involved in carotenoidbiosynthesis/catabolism in grapevine. The genes are distributed on 16 of the 19 chromosomesand have been localised to the physical map of the heterozygous ENTAV115 grapevinesequence. Nine of the genes occur as single copies whereas the rest of the carotenoidbiosynthetic genes have more than one paralogue. The cDNA copies of eleven correspondinggenes from Vitis vinifera L. cv. Pinotage were characterised, and four where shown to befunctional. Microarrays provided expression profiles of 39 accessions in the metabolicpathway during three berry developmental stages in Sauvignon blanc, whereas an optimisedHPLC analysis provided the concentrations of individual carotenoids. This provides evidenceof the functioning of the lutein epoxide cycle and their respective genes in grapevine.Similarly, orthologues of genes leading to the formation of strigolactone involved in shootbranching inhibition were identified: CCD7, CCD8 and MAX1. Moreover, the isoformstypically have different expression patterns, confirming the complex regulation of thepathway. Of particular interest is the expression pattern of the three VvNCEDs: Our resultssupport previous findings that VvNCED3 is likely the isoform linked to ABA content inberries. CONCLUSIONS: The carotenoid biosynthetic pathway is well characterised, and the genes and enzymes havebeen studied in a number of plants. The study of the 42 carotenoid pathway genes ofgrapevine showed that they share a high degree of similarity with other eudicots. Expressionand pigment profiling of developing berries provided insights into the most completegrapevine carotenoid pathway representation. This study represents an important referencestudy for further characterisation of carotenoid biosynthesis and catabolism in grapevine. |
