Roles of the GLABROUS1 and TRANSPARENT TESTA GLABRA Genes in Arabidopsis Trichome Development.

Arabidopsis trichomes are branched, single-celled epidermal hairs. These specialized cells provide a convenient model for investigating the specification of cell fate in plants. Two key genes regulating the initiation of trichome development are GLABROUS7 (GL7) and TRANSPARENT TESTA GLABRA (TTG). GL7 is a member of the myb gene family. The maize R gene, which can functionally complement the Arabidopsis ttg mutation, encodes a basic helix-loop-helix protein. We used constitutively expressed copies of the GL7 and R genes to test hypotheses about the roles of GL7 and TTG in trichome development. The results support the hypothesis that TTG and GL7 cooperate at the same point in the trichome developmental pathway. Furthermore, the constitutive expression of both GL7 and R in the same plant caused trichomes to develop on all shoot epidermal surfaces. Results were also obtained indicating that TTG plays an additional role in inhibiting neighboring cells from becoming trichomes.