Poly(A)-binding proteins act as a thermosensory switch to control flowering via cytoplasmic retention of RNA-binding...

Poly(A)-binding proteins (PABPs) are canonically recognized for their roles in mRNA-dependent processes through binding to the poly(A) tail of mRNA. However, whether PABPs possess functions distinct from their action on mRNA, particularly in controlling major developmental transitions, has remained unexplored. Here, we uncover a hitherto unknown role for two PABPs, PAB2 and PAB8, in flowering time control in Arabidopsis thaliana. We demonstrate that PAB2 and PAB8 interact with RNA-binding protein 45C (RBP45C) and determine its cytoplasmic retention. This prevents nuclear entry of RBP45C and its function in promoting the transcription and splicing of the key floral repressor FLOWERING LOCUS C (FLC). Furthermore, low ambient temperature attenuates the interaction between PAB2 and RBP45C, resulting in late flowering attributable to compromised cytoplasmic retention of RBP45C and elevated FLC expression. Our findings identify a non-canonical role of PABPs as a cytoplasmic anchor for RBP45C, which serves as a thermosensory switch of FLC expression to fine-tune flowering in response to cool ambient temperature.