DcNCED2 promotes ABA synthesis via carotenoid degradation and enhances drought resistance in carrot

Carrot DcNCED2 gene can improve the activity of antioxidant substances, enhance the drought tolerance of plant, and play regulatory roles in the degradation of carotenoids and the synthesis of ABA. Carrot (Daucus carota L.) is a biennial root vegetable crop of Apiaceae. In the process of growth and development, carrot is always subjected to drought stress, resulting in the decline of yield and quality. 9-cis-epoxycarotenoid dioxygenase (NCED) is an important rate-limiting enzyme in the pathway of carotenoid degradation and ABA synthesis, which can directly affect the drought resistance of plants. It is scientifically important to study the molecular mechanism of carrot DcNCED gene in response to drought stress. In this study, expression specificity analysis of DcNCED2 gene showed that the expression level of DcNCED2 gene reached the highest value at 60-75 d after sowing. DcNCED2 gene was transferred into Arabidopsis thaliana and carrot by constructing plant overexpression vector. The transgenic A. thaliana was found to exhibit a drought-tolerant phenotype with longer root length, higher SOD and POD activities, lower MDA content, higher ABA content and related gene expression, and lower lutein and β-carotene content. The results indicated that DcNCED2 gene could improve the drought tolerance of the seedling. The ABA content in leaf of overexpressed DcNCED2 carrot was significantly increased, while the contents of lutein, α-carotene and β-carotene were decreased compared with the wild carrot. The changes of expression levels of most related genes were consistent with the above results. These results indicated that DcNCED2 gene could promote the degradation of carotenoids and the synthesis of ABA in carrot leaves and thus achieve the regulation of abiotic stress in carrot plants.