Genome-wide analysis of the NF-Y gene family in non-heading Chinese cabbage and the involvement of BcNF-YA8 in ABA-mediated flowering regulation

The nuclear factor Y (NF-Y) is a class of heterotrimeric transcription factors comprising three subunits: NF-YA, NF-YB, and NF-YC. These transcription factors participate in many plant bioprocesses, including the regulation of flowering time. Although the NF-Y gene family has been systematically studied in many species, little is known about its role in the non-heading Chinese cabbage (NHCC) [Brassica campestris (syn. Brassica rapa) ssp. chinensis]. In this study, we identified 57 NF-Y members in the genome of NHCC using BLASTP, including 20 BcNF-YAs, 24 BcNF-YBs, and 13 BcNF-YCs. These genes are randomly distributed on the 10 chromosomes of NHCC. The results of yeast two hybrid experiments indicated that among some members of the three subunits of BcNF-Ys, the members of the NF-YA and NF-YC subunits interact with each other, a third of the members of the NF-YB and NF-YC subunits interact with each other, while no interaction was observed between the members of the NF-YA and NF-YB subunits. Subcellular localization experiments in tobacco showed that BcNF-YA2 and BcNF-YA8 were expressed in the nucleus; BcNF-YB18 and BcNF-YB23 were located in the cell membrane and cytoplasm; and BcNF-YC6 and BcNF-YC7 were expressed in the nucleus, cytoplasm, and cell membrane. We analyzed the cis-acting elements in the promoter of BcNF-Y genes and found that the ABA response element is the most distributed hormone response element, which is regulated by ABA signals triggered by environmental stimuli. Accordingly, we treated three-week-old NHCC leaves with 100 μmol · L-1 ABA and analyzed the expression profile of BcNF-Ys through RNA-seq. The results showed that except for six undetected BcNF-Ys, the remaining 51 BcNF-Ys showed varying degrees of response to ABA signals. Among these, BcNF-YA8 was positively regulated by ABA signals, with the highest upregulation amplitude. Subsequently, the function of BcNF-YA8 was extensively studied, which demonstrated that its expression promotes plant flowering. This result enriches our understanding of the potential molecular mechanism by which ABA positively regulates NHCC flowering.