Transcription repressor that binds specific DNA sequence such as GT3 box 5'-GGTAAA-3' in the SDD1 promoter (PubMed:21169508). Negative regulator of water use efficiency (WUE) via the promotion of stomatal density and distribution by the transcription repression of SDD1 (PubMed:21169508). Regulates the expression of several cell cycle genes and endoreduplication, especially in trichomes where it prevents ploidy-dependent plant cell growth (PubMed:19717615). Regulates negatively root hair growth by directly binding RSL4 promoter and repressing RSL4 expression (PubMed:29439132). Present within the nucleus during the postbranching stages of trichome development. A number of isoforms are produced. According to EST sequences. Mostly expressed in siliques, and, to a lower extent, in growing root hairs, leaves, stems, and flowers (PubMed:9501260). Present in abaxial epidermal cells, predominantly in guard cells, pavement cells, and meristemoids (PubMed:21169508). Down-regulated by water stress. Increased water deficit tolerance and higher integrated water use efficiency (WUE) by reducing daytime transpiration associated with a higher expression of SDD1 (PubMed:21169508). Increased trichome cell size with normal patterning and branching accompanied with an increase in the nuclear DNA content only in trichomes that have completed branching (PubMed:19717615). No visible phenotype under normal growth conditions, but the double mutant seedlings gtl1-1 and df1-1 exhibit increased root hair length (PubMed:29439132). Plants overexpressing GTL1 fail to develop root hairs. Probable cloning artifact.