Abstract
The CONSTANS (CO) gene in the long-day plant, Arabidopsis, and Hd1, the ortholog of CO in the short-day plant, rice, control mRNA expression of FT-group floral inducer genes and play a central role in photoperiodic flowering. CO induces FT mRNA in long-days, whereas Hd1 inhibits and induces mRNA expression of rice FT orthologs (Hd3a etc.) in long-days and short-days, respectively. Here, we analyzed the effects of CO /Hd1 on FT /Hd3a promoters by transient assays using rice protoplasts and Arabidopsis seedlings. We demonstrated that both CO and Hd1 act as a suppressor for Hd3a promoter in rice and act as an activator for FT promoter in both rice and Arabidopsis. Hd3a promoter was inactive in Arabidopsis. Therefore, the difference in FT/Hd3a promoters is a key in the regulation of FT/Hd3a genes by Hd1/CO. Responsible cis-elements in FT/Hd3a promoters are now being investigated.
