Cell-to-cell translocation of florigen is inhibited by low ambient temperature through abscisic acid signaling in Arabidopsis thaliana

In Arabidopsis thaliana , the FLOWERING LOCUS T ( FT ) gene encodes florigen, a floral stimulus that integrates multiple environmental cues to optimize the timing of flowering, which is crucial for reproductive success. The FT protein is synthesized in the phloem companion cells of leaves but exerts its function in the shoot apical meristem (SAM) to initiate floral morphogenesis. While the environment-dependent regulation of FT transcription in leaves is well studied, the mechanisms underlying FT transport, particularly its cell-to-cell translocation within the SAM, remain poorly understood. In this study, we employed an in vivo bimolecular fluorescence complementation assay to elucidate the molecular mechanisms regulating FT intercellular translocation in the SAM. We demonstrate that low ambient temperature inhibits the cell-to-cell movement of FT in the SAM through abscisic acid signaling pathways, resulting in flowering delay. We further show that the permeability of plasmodesmata (PD) is involved in FT transport; in particular, CALLOSE SYNTHASE ( CalS ) 1 and CalS7 are induced at low temperature, leading to reduced permeability of PD and inhibition of symplastic FT translocation in the SAM. Collectively, our findings provide insights into the molecular mechanisms that regulate the intercellular translocation of FT in the SAM in response to environmental conditions and lead to a framework for the understanding of flowering.