Objective To explore the function of short-chain dehydrogenases/reductases (SDRs) in safflower flavonoid, especially hydroxysafflower yellow A (HSYA) biosynthesis. Methods SDRs involved in HSYA biosynthesis pathway were screened based on safflower transcriptome database and metabolome database. The expression pattern was analyzed by qRT-PCR. The overexpression vector was constructed by seamless cloning technology, then genetically transformed to the Yunnan Weishan safflower strain by Agrobacterium gv3101. The transgenic T₂ generation plants were positively verified, and the gene expression of corolla SDRs was analyzed. The content of secondary metabolites was assayed by UPLC-Q-TOF/MS. Results Three SDRs genes named CtSDR1, CtSDR2 and CtSDR3 involved in HSYA biosynthesis pathway were screened. Their expression in safflower from high to low was corolla > leaf > stem > root. The expression level in corolla increased gradually with corolla development. qRT-PCR analysis of corolla with positive verification of genome insertion sequence showed that the transcription level of CtSDR3 in corolla of T₂ positive plants increased by 2~3 times compared with the blank control group, and the content of secondary metabolite HSYA increased by 7.1%~16.6% (P< 0.05). Conclusion CtSDR3 may be involved in the biosynthesis of flavonoids, especially HSYA, in safflower. It provides the support data for explaining the function of CtSDR3 in HSYA biosynthesis pathway.

Objective To explore the effect of circadian rhythm genes on flavonoids biosynthesis in safflower and its molecular mechanism. Methods Based on the transcriptome and metabolomic database of safflower corolla, we screened the circadian rhythm genes that correlate with biosynthesis of flavonoids in safflower. qPCR was used to quantify the expressions of circadian rhythm genes in different flowering stages at different time points in a single day. LC-MS was performed to determine the accumulation of flavonoids. The correlation between them was analyzed as well. Yeast Two-Hybrid experiment was used to verify the interactive proteins of these genes. Results Seven circadian rhythm genes PRR1, PRR2, ELF3, FT, PHYB, GI and ZTL were obtained. PRR1 gene was positively correlated with flavonoids accumulation (r≥0.7). The full length of PRR1 is 3 201 bp, encoding 421 amino acids, which is highly homologous with rice OsPRR73 gene and named as CtPRR1 (GenBank accession number: MW492035). CtPRR1 was mainly expressed in flowers, and the expression level increased in the daytime and declined in the evening gradually. Correspondingly, the content of flavonoids showed an opposite variation. Both of them displayed a circadian rhythm with a negative correlation (r≥−0.7). In addition, 2 heat shock proteins along with 3 AP2 transcription factors interacting with CtPRR1 protein were obtained via Yeast Two-Hybrid experiment. Conclusion CtPRR1 negatively regulated the safflower flavonoids accumulation in a circadian rhythm way, which may be affected by these interacting proteins.