Analysis of the function of CYCLING DOF FACTORS in flowering time control in Medicago truncatula

Abstract

Flowering time control is an important trait that is essential for the survival, world-wide adaptation and reproductive success of angiosperms. Flowering time also strongly affects crop quality and yield. Flowering time control has been intensely study in the model plant, Arabidopsis thaliana (Arabidopsis). In Arabidopsis, flowering time control is regulated by pathways that converge on key flowering time genes, such as FLOWERING LOCUS T (FT). Arabidopsis’ CYCLING DOF FACTORS (CDFs) are one of the crucial gene sets controlling photoperiod flowering time control. AtCDFs regulate flowering in several ways, most importantly by repressing a crucial flowering time regulator gene, CONSTANTS (CO) and by directly associating at the FT promoter. Like Arabidopsis, temperate legumes require a long day photoperiod to induce flowering. Conversely, no CO-like genes functioning in photoperiod flowering time control have been discovered in temperate legumes. Consequently, photoperiod flowering time control in legumes remains a mystery. However, CDF homologs have been identified in pea and Medicago truncatula (Medicago). In pea, the PsCDFc1 has been demonstrated to be involved in photoperiod flowering time control. As a result, the Medicago CDF homologs have been of interest. A previous student overexpressed MtCDF5 in Arabidopsis, which caused late flowering. In this thesis, MtCDF5 was overexpressed in Medicago by transformation by somatic embryogenesis. From the ten 35S:MtCDF5 lines created, plants from three of those lines flowered later than the wildtype regeneration controls. Additionally, another three CDF homologs, MtCDFa-c were overexpressed in Arabidopsis by floral dipping. All the 35S: MtCDFa-c transformants produced late flowering plants. Overexpression of MtCDFb and MtCDFc caused extreme late flowering. Additionally, several of the 35S: MtCDFc late flowering plants produced unusual phenotypes such as reverting back to vegetative state and producing aerial rosettes, similar to other Arabidopsis late flowering mutants. This further demonstrates that CDFs are likely to be important regulators of photoperiod flowering time control in plants and specifically in temperate legumes.