Physiological response of safflower to water deficit and genome-wide identification of its NAC transcription factor family.

Accumulated evidence demonstrated the major role of NAC transcription factors in plants response to drought stress. However, there are limited studies on the identification of safflower NAC genes and their functions in response to abiotic stress, i.e., water deficit. In the present study, a total of 85 CtNACs were identified and categorized into 17 subfamilies, and the vast majority of the CtNACs were annotated in biological process. Their promoters contained cis-regulatory elements related to light, hormonal and stress responses, and plant development. Moreover, physiological response of safflower to water deficit was assessed. Plant growth of safflower was downregulated during water deficit. The contents of osmotic adjustment substances (soluble sugar, soluble protein, proline), reactive oxygen species, malondialdehyde, hydrogen peroxide, and antioxidant enzymes activities, i.e., superoxide dismutase, peroxidase, catalase in safflower leaves were enhanced under water deficit. Additionally, the photosynthetic pigments in safflower were decreased during water stress. Moreover, quantitative real-time PCR detection revealed that the expression levels of most CtNACs were upregulated under water deficit, indicating that these genes may involved in the response of safflower to water deficit. These data facilitate the in-depth study of the biological functions of CtNACs and the breeding of drought-tolerant safflower varieties.