Figure 11.

A Model for the Role of DEK1, CR4, and SAL1 in Aleurone Cell Specification.

DEK1 at the surface of the endosperm is activated by an unknown mechanism (a), its calpain domain in the cytosol cleaving a postulated substrate (b) that leads to the specification of aleurone cell fate. DEK1 in all other positions is inactive (c). In cells with active DEK1 signaling, CR4 concentrates on plasmodesmata between aleurone cells (pda) and increases the plasmodesma exclusion limit, allowing the activated DEK1 substrate to move laterally between aleurone cells, thereby reinforcing the signal for aleurone cell fate specification (d). Plasmodesmata in cell walls between starchy endosperm cells are narrow (pds), whereas plasmodesmata in cell walls between aleurone cells and starchy endosperm cells are intermediary in width (pdi). DEK1 and CR4 are internalized by endocytosis (e) and traffic through endosomes. Whereas some DEK1 and CR4 molecules may be recycled back to the plasma membrane (f), others are sorted for degradation in the vacuole in a process that requires SAL1. Some endosomes are recycled back to the plasma membrane (f).