Quantification of the Relative Abundance of Plastome to Nuclear Genome in Leaf and Root Tissues of Carrot (Daucus carota L.) Using Quantitative PCR

Abstract

Carrot (Daucus carota L.) is an important horticultural crop with significant health benefits, providing provitamin 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 chromoplasts, non-chlorophyll-containing plastids, in non-photosynthetic organs such as the storage roots of carrot. Therefore, plastid development is closely associated with carotenoid accumulation. 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 carrot storage root. In this study, the plastome was confirmed to occur in similar relative abundance (plastome–nuclear genome ratio) in yellow and orange carrot storage roots while dark orange storage roots had significantly higher plastome content than white cultivated carrots. In the leaf tissue of these same plants, the relative abundance of the plastome was similar across genotypes but was lower than the ratio of plastid to nuclear genome in the root tissue of pigmented storage rooted carrot. This study is the first quantification of the ratio of plastome to nuclear genome in storage root and confirms the presence of the plastome in both pigmented and non-pigmented carrot storage root tissue.