Photoperiodic control of floral transition in Arabidopsis thaliana
Final Report Abstract
The induction of flowering is a central event in the life cycle of plants. When timed correctly, it helps ensure reproductive success, and therefore has adaptive value. Because of its importance, flowering is under the control of a complex genetic circuitry that integrates endogenous and environmental signals. The later include temperature, both ambient growth temperature and exposure to prolonged period of cold (vernalization) and light. It has been long proposed that photoperiod (day length) is perceived in leaves where it leads to the induction of a flower-forming substance, or ʻflorigenʼ. The florigen is then transmitted to the growing tip of the plant, the shoot apex, where it induces the transition to flowering. The molecular nature of florigen has eluded characterization for 70 years. An important aspect of this project has been to analysis of the function of the FLOWERING LOCUS T (FT) protein and its potential as a ʻflorigenʼ. Our results indicate that movement of the FT protein from the phloem companion cells to the shoot meristem is both necessary and sufficient to induce flowering in Arabidopsis thaliana, making FT a very likely ʻflorigenʼ. At the shoot meristem, FT is known to interact with the bZIP transcription factor FD. Using 2nd generation sequencing coupled to chromatin-immunoprecipitation (ChIP-seq) in conjunction with transcriptome analyses (RNA-seq; microarrays) we have identified direct transcriptional targets of FD across the Arabidopsis genome. Among these targets of FD are many known regulators of flowering time and floral patterning, suggesting that FT/FD regulate flowering rather directly. In addition to our work on the function of FT and FD in regulating the floral transition, we have also studied the role of two repressors of flowering, SCHALFMÜTZE (SMZ) and APETALA 2 (AP2) in regulating the expression of FT and other known flowering time genes. Here we could show that the A-class homeotic protein AP2 and related transcription factors such as SMZ directly control expression of numerous flowering time and flower development genes. Furthermore, SMZ apparently requires the function of the type II MADS-domain transcription factor FLOWERING LOCUS M to repress flowering.
Publications
- (2007). Export of FT protein from phloem companion cells is sufficient for floral induction in Arabidopsis. Curr. Biol., 17, 1055-1060
Mathieu, J., Warthmann, N., Küttner, F., Schmid, M.
- (2009). Just say no: floral repressors help Arabidopsis bide the time. Curr. Opin. Plant Biol., 12, 580-586
Yant, L. J., Mathieu, J., Schmid, M.
- (2009). Repression of flowering by the miR172 target SMZ. PLoS Biol., 7, e1000148
Mathieu, J., Yant, L. J., Mürdter, F., Küttner, F. Schmid, M.
- (2010). Orchestration of the floral transition and floral development in Arabidopsis by the bifunctional transcription factor APETALA2. Plant Cell, 22, 2156-2170
Yant, L. J., Mathieu, J., Dinh, T. T., Ott, F., Lanz, C., Wollmann, H., Chen, X., Schmid, M.
