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Title: Quantification of the relative abundance of plastome to nuclear genome in leaf and root tissues of carrot (Daucus carota L.) using quantitative PCR

Author
item BOWMAN, MEGAN - University Of Wisconsin
item Simon, Philipp

Submitted to: Plant Molecular Biology Reporter
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/26/2012
Publication Date: 1/12/2013
Citation: Bowman, M.J., Simon, P.W. 2013. Quantification of the relative abundance of plastome to nuclear genome in leaf and root tissues of carrot (Daucus carota L.) using quantitative PCR. Plant Molecular Biology Reporter. 31(4):1040-1047.

Interpretive Summary: Carotenoids include orange, red, and yellow pigments that are naturally found in plants. The orange and red carotenoids are called carotenes, whereas the yellow carotenoids are called xanthophylls. Orange carotenes account for the familiar color and also the high nutritional value of carrots, while yellow carrots contain xanthophylls. Not all carrots accumulate carotenoid pigments, and they are white. All carotenoids accumulate in structures within plant cells called plastids, and plastids include not only these pigments, but also a small circle of genes called a plastome. In this study we determined whether orange, yellow and white carrots all contained plastomes. We found that carrots of all three colors had similar amounts of plastome, even though white carrots contained no carotneoids. These findings are of interest to plant molecular biologists, biochemists, and geneticists.

Technical Abstract: Carrot (Daucus carota L.), is an important horticultural crop with significant health benefits, providing pro-vitamin A carotenoids in the human diet. Carotenoids primarily serve as photoprotectants in leaves during photosynthesis where they accumulate in chloroplasts. Carotenoids can also accumulate in storage roots, as is found in carrot, where they accumulate in chromoplasts, non-chlorophyll containing plastids. Therefore, plastid development is closely associated with carotenoid accumulation. While much is understood about the carotenoid biosynthetic pathway in plants, the mechanism of accumulation, particularly in root tissue, is not well understood. The biosynthesis of chromoplasts, or more specifically the conversion of chloroplasts to chromoplasts, has been studied in a number of carotenoid accumulating plant species, but the presence of the plastome had not been confirmed in non-pigmented or pigmented carrot storage root. In this study, the plastome was confirmed to occur in similar relative abundance (plastome/nuclear genome ratio) in white, yellow, and orange carrot storage roots but dark orange storage roots had significantly higher (1.4-2x) plastome content than white cultivated carrots. In the leaf tissue of these same plants, the relative abundance of the plastome was generally lower than in the root but relatively similar across genotypes. This study is the first quantification of the ratio of plastome to nuclear genome in storage root, and confirms the presence of the carrot plastome in non-pigmented carrot storage root tissue.