Explosive seed launch requires ABCG32 for cuticle formation
Résumé
Exploding seed pods of the common weed Cardamine hirsuta have the remarkable ability to launch their seeds far from the plant. During explosive seed dispersal, the kinetic energy in the coiling fruit valves is transferred to launch the seeds. But how this is achieved is unknown. We took a genetic approach to address this question by screening for seed launch mutants. We identified an ATP-binding cassette G32 (ABCG32) mutant with explosive fruit that often failed to launch seeds. ABCG32 was expressed in the epidermis of aerial organs and loss of ABCG32 resulted in a permeable cuticle. By TEM, we observed perforations in the seed coat cuticle, associated with a significant decrease in cutin monomers. We found that pectin epitopes in the cell wall were exposed at the seed surface where the cuticle is discontinuous. It required more force to pull these 'sticky' seeds away from the fruit, suggesting that a continuous cuticle is needed to effectively launch seeds in C. hirsuta.