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. Contents Summary 9 I. Introduction 10 II. Cuticle structure 10 III. Cuticular waxes 10 IV. Cell patterning in the epidermis 11 V. Stomatal development 12 VI. Stomatal development in dicotyledonous plants 12 VII. Mutants in stomatal development 14 VIII. Control of Stomatal Development 14 IX. Cuticle composition affects stomatal development 14 X. The HIC - HI gh Carbon dioxide gene 15 XI. Fatty acid elongases 17 XII. The cuticle: an alternative signalling medium? 17 XIII. Trichome development 18 XIV. Cuticle composition affects trichome development 19 XV. Cuticle composition affects pollen germination 20 XVI. Conclusions 20 Acknowledgements 21 References 21.