Transcription factor involved in auxin response. Functions in auxin signal transduction and modulates lateral root growth. Interacts with ARF response factors to promote auxin-responsive gene expression (PubMed:17675404). In response to auxin, binds sequence-specific motifs in the promoter of the auxin-responsive gene IAA19, and activates IAA19 transcription. The IAA19 transcription activation by MYB77 is enhanced by direct interaction between MYB77 and PYL8 (PubMed:24894996). Interacts with ARF1, ARF7 and IAA19 (PubMed:17675404). Interacts with PYL8 (PubMed:24894996). Expressed in roots, stems and flowers. Expressed in dry seeds (PubMed:9678577). Expressed in root vasculature, root tips and lateral root (PubMed:17675404). Expressed in leaves from the third leaf to rosette leaves from six-week old plants. Expression follows a development-dependent gradient in successive leaves. Induced by auxin (PubMed:17675404). Down-regulated by potassium deprivation (PubMed:15173595). No visible phenotype under normal growth conditions. Plants overexpressing MYB77 exhibit stunted roots and shoots.