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

Abstract

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.