Novel transcriptional activator TAC3 regulates age-dependent floral transition in Chinese fir

Plant undergo juvenile-to-adult transition to become competent for age-dependent floral induction and reproductive transition, which is of great significance for improving the seed quality and maintaining desirable genetic traits of Chinese fir, but the underlying molecular mechanize still remains unknown. Here, we investigated the function of our newly identified spermatophyte specific transcriptional co-activator TAC3 (Transcriptional Activator in Chinese fir 3) and its homologues (TAL1) in the model plant Arabidopsis. Both TAC3 and TAL1 can negatively regulate flowering, and activate miR156 expression to delay the phase transition. Moreover, we found that HDA9 and its its homologues in Chinese fir, ClHDA9, can directly binding to the promoter region of MIR156A and ClMIR156A, respectively. Directly interaction with ClHDA9 and HDA9 are necessary for the transcriptional activation of TAC3 and TAL1 on miR156, respectively. TAC3 and TAL1 also involve in the chromatin remodeling, shown as up-regulated H3K27ac level within the promoter region of ClMIR156A and MIR156A. Together, this work shows that TAC3 and its homologues are a new group of transcriptional co-activator that involving in aging-dependent flowering signal pathway of both angiosperms and gymnosperms. ### Competing Interest Statement The authors have declared no competing interest.