Involvement of PtCOL5-PtNF-YC4 in reproductive cone development and gibberellin signaling in Chinese pine

It is well documented that the CO/NF-YB/NF-YC trimer (NF-Y-CO) binds and regulates the FT promoter. However, the FT/TFL1-like (FLOWERING LOCUS T/TERMINALFLOWER1-like) genes in gymnosperms are all flowering suppressors, and the regulation model of NF-Y in gymnosperms is different from that in angiosperms. Here, using Chinese pine (Pinus tabuliformis), we identified a CONSTANS-LIKE gene, PtCOL5, the expression of which was strongly induced during cones development and it functioned as a repressor of flowering. PtNF-YC4, which interacted with PtCOL5, was highly correlated with PtCOL5 during growth and development, has been demonstrated. Moreover, PtNF-YC4 and PtCOL5 can bind to PtTFL2 promoter, and their interaction can enhance PtTFL2 expression. Interestingly, we found PtNF-YC4 and PtCOL5 were involved in gibberellin signaling and their interaction was inhibited by PtDELLA protein, thus affecting PtTFL2 expression. Collectively, PtCOL5-PtNF-YC4 was involved in reproductive cone development and gibberellin signaling in Chinese pine. Our findings uncovered reproductive cone development and signal transduction mechanism of COL-NF-Y in gymnosperms.