Integrating transcriptomics and metabolomics to studies key metabolism, pathways and candidate genes associated with drought-tolerance in Carthamus tinctorius L. Under drought stress

Considering the changes of precipitation and soil moisture caused by climate change, it was important to understand the mechanism of plant response to water shortage. Moreover, the anti-drought character of the safflower (Carthamus tinctorius L.) was an ideal choice for studying the molecular and biochemical mechanisms of drought resistance in oil crop. In this paper, the transcription and metabolic response of the two different drought-resistant genotypes of safflower (the drought-intolerant accession PI560169 and the drought-tolerant accession PI401477) were studied. The leaf relative water contents (RWC), chlorophyll contents, and morphological changes of the leaves of safflower plants were seriously affected by the water-deficient conditions, while antioxidant compounds (catalase and superoxide dismutase) and osmotic adjustment substances (soluble protein and proline) were significantly increased. Under drought and abundant water conditions, 3280 and 2260 differentially expressed genes (DEGs) were identified in PI401477 and PI560169, respectively. In addition, 359 and 209 differential metabolites (DMs) were identified between the two treatments in PI401477 and PI560169, respectively. The combined analysis of transcriptomics and metabolomics data revealed certain aspects of metabolic regulation under drought stress. Firstly, several key candidate genes, such as MYB62, MYB2, NECD4, ABA2, CYP707A4, ZDS, GolS1, P5CS1, GST23, GST3, GSTL1, Cu-ZnSOD1, OEE2 and ALDH3F1 were more likely to determine safflower drought resistance. Secondly, it was found that three metabolites (galactitol, neoxanthin and arbutin) were correlated with drought-tolerance and differently regulated in these two genotypes. Thirdly, several key candidate genes and metabolites were found belonged to the 8 metabolic pathways, which suggested the importance of these metabolic pathways during drought stress. These results provided a new insights into the complex mechanisms of drought response in safflower or other oil crops.