FLOWERING LOCUS C integrates carbon and nitrogen signaling for the proper timing of flowering in Arabidopsis

The timing of flowering in plants is modulated by both carbon (C) and nitrogen (N) signaling pathways. In a previous study, we established a pivotal role of the sucrose-signaling trehalose 6-phosphate pathway in regulating flowering under N-limited short-day conditions. In this work, we expand on our finding that wild-type plants grown under N-limited short days require an active trehalose 6-phosphate pathway to be able to flower. Both wild-type plants grown under N-limited conditions and knock-down plants of TREHALOSE PHOSPHATE SYNTHASE1 induce FLOWERING LOCUS C expression, a well-known floral repressor associated with the vernalization response. When exposed to an extended period of cold, a mutant of FLOWERING LOCUS C fails to respond to N availability, and flowers at the same time under N-limited and full-nutrition conditions. Our data suggest that SUCROSE NON-FERMENTING 1 RELATED KINASE 1-dependent trehalose 6-phosphate-mediated C signaling and a novel mechanism downstream of N signaling likely involving NIN-LIKE PROTEIN 7 impact the expression of FLOWERING LOCUS C. Collectively, our data underscore the existence of a multi-factor regulatory system in which both C and N signaling pathways jointly govern the regulation of flowering in plants.