To achieve a greater understanding of the regulation of cotton fibre differentiation, more fundamental information is needed on the signals and mechanisms associated with fibre initiation. The extensive genetic knowledge of Arabidopsis leaf trichomes could aid in the elucidation of the genetic mechanisms controlling cotton fibre differentiation. Trichomes are small hairs on the plant surface, originating from single epidermal cells in a developmental process that appears very similar to that of cotton fibres. Arabidopsis trichome development has been extensively investigated, and several genes that control the process have been characterised. One gene essential for trichome initiation is TRANSPARENT TESTA GLABRA1 (TTG1), and loss-of-function mutations in TTG1 result in an almost complete absence of leaf trichomes. TTG1 plays additional roles in numerous pathways in Arabidopsis, including root hair initiation, anthocyanin production and seed coat mucilage production. In order to isolate genes required for fibre initiation in cotton, functional homologues of Arabidopsis TTG1 in cotton have been sought.

Four putative homologues of Arabidopsis TTG1 have previously been isolated in this laboratory by RT-PCR of mRNA prepared from cotton fibres, and are termed GhTTG1-4. Sequence comparisons between the four cotton deduced proteins and Arabidopsis TTG1 showed that they form two groups, with GhTTG1 and GhTTG3 being closely related to each other (87% identical and 93% similar) and to TTG1 (79% and 80% amino acid identity respectively). GhTTG2 and GhTTG4 formed the second group, with 95% amino acid identity to each other and lower (approximately 62%) identity to TTG1. An analysis of the genomic originis of the GhTTG genes demonstrated that each is derived from the same ancestral diploid genome.