The genes crucial to carotenoid metabolism under elevated CO levels in carrot (Daucus carota L.).

The CO saturation point can reach as high as 1819 μmol· mol in carrot (Daucus carota L.). In recent years, carrot has been cultivated in out-of-season greenhouses, but the molecular mechanism of CO enrichment has been ignored, and this is a missed opportunity to gain a comprehensive understanding of this important process. In this study, it was found that CO enrichment increased the aboveground and belowground biomasses and greatly increased the carotenoid contents. Twenty genes related to carotenoids were discovered in 482 differentially expressed genes (DEGs) through RNA sequencing (RNA-Seq.). These genes were involved in either carotenoid biosynthesis or the composition of the photosystem membrane proteins, most of which were upregulated. We suspected that these genes were directly related to quality improvement and increases in biomass under CO enrichment in carrot. As such, β-carotene hydroxylase activity in carotenoid metabolism and the expression levels of coded genes were determined and analysed, and the results were consistent with the observed change in carotenoid content. These results illustrate the molecular mechanism by which the increase in carotenoid content after CO enrichment leads to the improvement of quality and biological yield. Our findings have important theoretical and practical significance.