Abstract
Unlike most flowering plant species, kiwifruit (Actinidia species) are dioicous having separate male and female plants. Female kiwifruit flowers contain ovaries which develop into fruit (the commercial product) and produce non-viable pollen. Conversely, male kiwifruit flowers produce viable pollen to fertilize the eggs of female kiwifruit but have no ovary and therefore cannot produce fruit. As such, male kiwifruit vines have largely unknown fruiting genetics. The generation of a kiwifruit vine with known high quality fruiting genetics which also produces viable pollen would greatly benefit kiwifruit breeding programmes. One of the routes proposed is to restore pollen viability to female kiwifruit plants generating a male-fertile female kiwifruit vine.
Friendly Boy (FrBy) has been identified as the male fertility factor in kiwifruit and is only inherited by male kiwifruit plants. Female kiwifruit plants transformed to express FrBy are male fertile producing pollen capable of fertilising egg cells. Therefore, the application of signalling molecules downstream of FrBy has been hypothesised to be able to restore pollen viability to female kiwifruit plants without genetic modification. To develop such a treatment, further understanding of how FrBy promotes correct pollen development is required.
This research project further characterised the kiwifruit FrBy protein (KFrBy) and the Arabidopsis thaliana homologue AFrBy through in silico analysis. Both KFrBy and AFrBy were predicted to contain signal peptides and GPI-anchors. These features lead to the hypothesis that mature FrBy proteins anchor to the plasma membrane facing into the apoplast (extra cellular space). This hypothesis was supported for AFrBy through the generation and transient expression AFrBy-GFP fusion protein constructs.
In this research, FrBy overexpression experiments were conducted in A. thaliana. These experiments showed that constitutive overexpression expression of AFrBy in A. thaliana leads to total pollen abortion. As only half of the developing pollen grains would contain the transgene, AFrBy has been hypothesised to act within a signalling cascade regulating all pollen. KFrBy and AFrBy have further been hypothesised to signal through protein-protein interactions via the predicted Fasciclin 1 domains which are conserved across the two homologues.