Transcription repressor that negatively regulates root hair growth by directly binding RSL4 promoter and repressing RSL4 expression (PubMed:29439132). Required for the synthesis of seed coat mucilage (PubMed:22735692, PubMed:25658798). No visible phenotype under normal growth conditions, but the double mutant seedlings gtl1-1 and df1-1 exhibit increased root hair length (PubMed:29439132). Reduced amount of seed coat mucilage (PubMed:22735692, PubMed:25658798). Plants overexpressing DF1 exhibit very short root hairs.