Tapetum and middle layer control of male fertility in kiwifruit

Kiwifruit (Actinidia deliciosa) male-sterile anthers abort at the microspore-stage, but the role sporophytic tissues in controlling male-sterility is unknown. Falasca et al. show that the tapetum and middle-layer exhibit secretory activity and degenerate by programmed cell death (PCD), but PCD is later in male-sterile than in male-fertile anthers. Calcium accumulates in cell walls of the middle layer and tapetum and in the exine of microspores and pollen, reaching higher levels in male-sterile anthers. They conclude that male sterility in kiwifruit is induced by anther wall tissues through prolonged secretory activity caused by a delay in PCD, in the middle layer in particular. In vitro culture results support the sporophytic control of male fertility and open the way to applications to overcome dioecism and optimize kiwifruit production.