Genome-Wide Classification and Abiotic Stress-Responsive Expression Profiling of Carotenoid Oxygenase Genes in Brassica rapa and Brassica oleracea

Carotenoid oxygenase is a key enzyme involved in the metabolism of carotenoids, which are important quality factors affecting the pigmentation and aroma of flowers and fruits, as well as main regulators of plant phytohormones, such as abscisic acid (ABA) and strigolactone (SL). To investigate the regulation of carotenoid metabolism, including ABA and SL biosynthesis by carotenoid oxygenase genes, in B. rapa and B. oleracea, we studied the expression of these genes in response to salt, drought, cold, ABA, and SL treatments. In the Brassica database, we identified genes related to carotenoid cleavage dioxygenase (CCD) 1, CCD4, CCC7, CCD8, NCED (9-cis-epoxycarotenoid dioxygenase) 2, NCED3, NCED5, NCED 6, and NCED9. We classified 15 and 14 carotenoid oxygenase candidate genes in B. rapa and B. oleracea, respectively. CCD1 and CCD4 showed similar transcription trends under abiotic stress treatment conditions in both B. rapa and B. oleracea, with expression peaking at 3-6 h post treatment before decreasing at 12 h. NCED2, NCED6, and NCED9 were responsive to ABA and SL treatments. Our results show that the phytohormone biosynthetic enzymes involved in carotenoid oxygenase pathways may be activated as multifunctional stress signaling factors with a variety of transcriptional responses via their interactions under abiotic stress treatment conditions in B. rapa and B. oleracea.