Fig. 5
CO1 negatively regulates FTL9 in B. distachyon. a qPCR analysis of FTL9 expression in four-week-old wild-type Bd21-3 and two independent CO1-RNAi (CO1-R) lines under LDs. Error bars indicate s.d. (Student’s t test, *P < 0.05). b qPCR analysis of FTL9 expression in four-week-old wild-type Bd21-3 and two independent CO1 overexpressing (CO1-O) transgenic lines under SDs. Error bars indicate s.d. (Student’s t test, **P < 0.01, ***P < 0.001). c Examination of CO1 repressive activity to FTL9 in N. benthamiana leaves. Left: Representative photograph of firefly luciferase fluorescence signals when the indicated reporter and effectors were introduced in N. benthamiana leaves. Right: Relative reporter activity (LUC/REN) in N. benthamiana leaves expressing the indicated reporters and effectors. Error bars indicate s.d. (Student’s t test, **P < 0.01). d A working model for the regulatory pathway of flowering initiation in B. distachyon under different day lengths. FTL9 can constitute a FAC with FD1 to trigger flowering, but the flowering inductive efficiency of FTL9-FAC is much lower than that of FT1-FAC, thereby resulting in a positive role of FTL9 in plant reproductive transition when FT1 is not expressed, while a dominant-negative role when FT1 is accumulated. The transcription and stabilization of CO is largely dependent on light in plants. In temperate grass, a CO ortholog, CO1, functions as a activator of FT1 whereas a repressor of FTL9. The decrease of CO1 mRNA and protein under SDs leads to an inhibition of FT1 and a release of FTL9, which makes plants a delay but an eventual floral onset in the non-inductive photoperiod. When plants grow under LDs, the accumulation of CO1 mRNA and protein is able to lead to a significant increase of FT1 and a dramatic reduction of FTL9, which triggers a rapid flowering
