Abstract:
Flowering is important to the sexual reproduction of angiosperm plants, and this division of the plant kingdom has evolved molecular pathways for sensing a variety of exogenous and endogenous cues to determine when to flower. This thesis research was aimed to analyse the function and conservation of two genes involved in the regulation of flowering in the legume (Fabaceae family) plant species Medicago truncatula: MtSVP-1 and MtSVP-2. In the model plant Arabidopsis thaliana (Brassicaceae family), the SHORT VEGETATIVE PHASE (SVP) gene encodes a MADS-box transcription factor that represses the floral transition and is influenced by the autonomous pathway, ambient temperature, the circadian clock and the plant hormone, gibberellin. SVP also has a partially redundant role after the floral transition, repressing homeotic floral patterning genes in the early floral meristem. Previous work has shown that MtSVP-1 overexpression in A. thaliana causes delayed flowering and an abnormal floral phenotype, similar to SVP overexpression phenotypes. To analyse whether MtSVP-2 function was also conserved, it was cloned into an overexpression vector and transformed into A. thaliana wild-type and non-functional svp lines via the floral dip method. Results were promising; T1 generations of MtSVP-2 overexpressors had moderate floral abnormalities and some T2 progeny had strong delays in flowering time. To analyse the endogenous function of the MtSVP genes, it was proposed to overexpress them in M. truncatula via tissue culture. Since MtSVP-2 had not yet been cloned, it could not be transformed into M. truncatula as the tissue culture process takes 5 – 7 months. However an MtSVP-1 overexpression construct had been cloned previously, and in parallel to MtSVP- 2 cloning this overexpression construct was transformed into M. truncatula. Analysis of the T0 transformants and their progeny showed that MtSVP-1 overexpression caused a mild delay in flowering time and slight alteration of floral patterning in M. truncatula. The phenotypes of the MtSVP-1 and MtSVP-2 overexpression lines in this thesis and previous work suggests that although both Medicago homologs have SVP-like function when overexpressed in A. thaliana, MtSVP-1 overexpression does not cause a major change to flowering in M. truncatula. This could suggest that MtSVP-1 function is already saturated in this species, or that MtSVP-1 has diverged in function compared to its A. thaliana homolog.