Genome-wide characterization of carotenoid oxygenase gene family in three cotton species and functional identification of GaNCED3 in drought and salt stress.

Cotton that serves natural fiber for the textile industry is an important industrial crop. However, abiotic stress imposed a significant negative impact on yield and quality of cotton fiber. Carotenoid cleavage oxygenases (CCOs) that specifically catalyze the cleavage of carotenoid are essential for plant growth and development and abiotic stress response. While information of cotton CCOs and their potential functions in abiotic stress is still far from satisfactory, which imposes restrictions on application in genetic breeding for stress resistance. In this study, 15, 15, and 30 CCOs were identified from Gossypium arboreum, Gossypium raimondii, and Gossypium hirsutum, respectively. Phylogenetic relationship indicated that CCO genes could be classified into two groups (NCEDs and CCDs). Cis-elements prediction showed that there were 18 types of stress-related cis-elements in promoter regions. Analysis with transcriptome data revealed tissue-specific expression pattern of cotton CCOs. qRT-PCR analysis revealed only that GhNCED3a_A/D and GhNCED3c_A/D had strong response to drought, salt, and cold stress, while GhCCD1_A/D and GhCCD4_A showed relatively slight expression changes. Virus-induced gene silencing of GaNCED3a, the ortholog gene of GhNCED3a_A/D, suggested that silenced plants exhibited decreased resistance not only to drought but also to salt, with significantly reduced proline content, and high malondialdehyde content and water loss rate. In addition, stress response genes RD29A, DREB1A, and SOS1 significantly downregulated under drought and salt stress in silenced plants compared to control plants, indicating that GaNCED3a played an important role in drought and salt response. The results provided valuable insights into function analysis of cotton CCOs in abiotic stress response, and suggested potential benefit genes for stress-resistant breeding.