The developmental and genetic basis of explosive pod-shatter in cardamine hirsuta

Dispersal is a key trait across biology. Within plants, a variety of explosive seed dispersal mechanisms are seen. Whilst ecological and mechanical studies have described this important evolutionary adaptation in many species, a genetic and developmental understanding of explosive seed dispersal is lacking. In this thesis, the morphology and development of the explosive seed pods of Cardamine hirsuta – a member of the Brassicaceae – are characterised in detail, with reference to its close relative, the model organism A. thaliana. Comparison of fruit morphology between these two species and across other Brassicacean species generated hypotheses regarding the function and polarity of morphological features. In order to identify genes that are necessary for C. hirsuta fruit development, a genetic screen was conducted and a range of mutants identified and subsequently characterised. Analysis of the indehiscent valveless (val) mutant revealed a loss of valve tissue and an expansion of valve margin identity in the silique. Mapping and sequencing identified a mutation in the MADS-box gene FRUITFULL (FUL), which results in a truncated protein, as the likely cause of the val phenotype. Consideration of ful mutants in C. hirsuta and A. thaliana allowed comparison of the genetic patterning of the fruit dehiscence zone in these two species. The genetic interactions between fruit mutants characterised in this thesis and mutants in shoot patterning genes revealed common regulatory networks underlying leaf and fruit development in C. hirsuta. Together, comparison of wild-type and mutant C. hirsuta siliques with those of A. thaliana and other Brassicacean species suggests that specialised cell layers within the valve silique region are of key importance to C. hirsuta’s explosive dehiscence mechanism.