Transcription activator, when associated with MYB75/PAP1, MYB90/PAP2 or TT2. Involved in epidermal cell fate specification. Regulates negatively stomata formation, but, in association with TTG1 and MYB0/GL1, promotes trichome formation, branching and endoreplication. Regulates also trichome cell wall maturation. Together with MYB66/WER, promotes the formation of non-hair cells in root epidermis cells in the N position. Whereas together with CPC, promotes the formation of hair cells in root epidermis cells in the H position by inhibiting non-hair cell formation. Seems also to play a role in the activation of anthocyanin biosynthesis, probably together with MYB75/PAP1. Activates the transcription of GL2. Efficient DNA binding requires dimerization with another bHLH protein (By similarity). Homodimer and heterodimer with BHLH2. Interacts directly with TTG1 and MYB0/GL1 to form a complex. Its interaction with TRY prevents MYB0/GL1 binding. Interacts with MYB75/PAP1, MYB90/PAP2, TT2, CPC, MYB23 and MYB66/WER. Interacts with MYB82 (PubMed:24803498). Moves from developing hair cells (trichoblasts) to developing non-hair cells (atrichoblasts). Also detected in trichome nucleus. Mostly expressed in roots and flowers. Also present in stems and leaves, and, to a lower extent, in hypocotyls. Expressed in epidermal root hair cells (trichoblasts) and moves to root hairless cells (atrichoblasts) by a cell-to-cell movement through plasmodesmata (at protein level). Localized in trichome developing region of leaves, prior to trichome initiation. Levels increase in initiating and young trichome cells, but dropped in the pavement cells between trichomes. Disappears in mature trichomes. By nitrogen deficiency and UV light. Negatively regulated by MYB66/WER, GL3 and BHLH2 in the developing non-hair cells, and positively regulated by CPC and TRY in the developing hair cells. Plants exhibit two-branched trichomes instead of three-branched trichomes.