GLABROUS1 overexpression and TRIPTYCHON alter the cell cycle and trichome cell fate in Arabidopsis

Cellular competence, initiation cues, and inhibition signals control the distribution of trichomes on the Arabidopsis leaf. The GLABROUS1 (GLI) gene has a dual role in that it is required for trichome initiation, but GLI overexpression reduces trichome number. We have found that a mutation in the TRIPTYCHON (TRY) gene partially suppresses the GLI overexpression phenotype but not in a way that indicates that TRY directly controls an epidermal inhibition pathway. Surprisingly, cauliflower mosaic virus 35S::GLI try plants contain a subclass of trichomes derived from the subepidermal layer. Altered cell cycle control was also detected in 35S::GLI and try plants. A mutation in TRY led to increased epidermal and mesophyll cell number, a reduction in endoreduplication in the epidermis, and an increase in endoreduplication in trichomes. GL1 overexpression also reduced endoreduplication levels in both the epidermis and trichomes; however, in the presence of try, it synergistically enhanced trichome endoreduplication. Interactions with the COTYLEDON TRICHOME1 (COM) gene indicate that GLI and TRY control trichome development and may be involved in cell cycle control during leaf development.