Signals from the cuticle affect epidermal cell differentiation

Studies of Arabidopsis wax biosynthesis mutants indicate that the control of cell fate in the aerial epidermis is dependant upon the synthesis of the waxy cuticle that overlies the epidermal layer. Several cer mutants, originally isolated as wax deficient, not only affect cuticular wax composition but also exhibit large increases in stomatal numbers. Stomatal numbers are also affected in hic mutant plants, but despite HIC encoding a putative wax biosynthetic enzyme the hic phenotype of increased stomatal numbers is more subtle, and only seen at elevated CO2 concentrations. This suggests that environmental effects on stomatal number may be mediated through cuticular wax composition. Other putative wax biosynthetic genes, FDH and LCR, have effects on the number of trichomes that develop in the epidermis, indicating that trichome development may also be affected by cuticle composition. Thus signals from the cuticle may influence how trichome and stomatal numbers in the epidermis are determined. Wax components could be the developmental signalling molecules, or could be the mediating medium for such signals, stimulated by environmental cues, which affect epidermal cell fate.