ABI5-BINDING PROTEIN2 Coordinates CONSTANS to Delay Flowering by Recruiting the Transcriptional Corepressor TPR2.

ABI5-BINDING PROTEIN2 (AFP2) negatively regulates the abscisic acid signal by accelerating ABI5 degradation during seed germination in Arabidopsis (). The abscisic acid signal is reported to delay flowering by up-regulating expression, but the role of AFP2 in regulating flowering time is unknown. Here, we found that flowering time was markedly delayed and () expression was reduced in a transgenic Arabidopsis line overexpressing under LD conditions. Conversely, the loss-of-function mutant showed slightly earlier flowering, with higher expression. These data suggest that negatively regulates photoperiod-dependent flowering time by modulating the CO signal. We then found that exhibited circadian expression rhythms that peaked during the night. Furthermore, the C-terminus of AFP2 interacted with CO, while its N-terminal ethylene response factor-associated amphiphilic repression motif interacted with the transcriptional corepressor TOPLESS-related protein2 (TPR2). Thus, AFP2 bridges CO and TPR2 to form the CO-AFP2-TPR2 complex. Biochemical and genetic analyses showed that AFP2 mediated CO degradation during the night. AFP2 also recruited histone deacetylase activity at chromatin through its interaction with TPR2. Taken together, our results reveal an elaborate mechanism by which AFP2 modulates flowering time through coordinating the activity and stability of CO.