Transcription factor that acts as molecular switch in the NAC012/SND1-mediated transcriptional network regulating secondary wall biosynthesis. Is directly activated by NAC012/SND1 and its close homologs, including NAC043/NST1, NAC066/NST2, NAC101/VND6 and NAC030/VND7. Is required for functional expression of a number of secondary wall-associated transcription factors and secondary wall biosynthetic genes involved in cellulose, xylan and lignin synthesis. Functions redundantly with MYB46 in the transcriptional regulatory cascade leading to secondary wall formation in fibers and vessels (PubMed:19808805). Transcription activator that binds to the DNA consensus sequence 5'-ACC[AT]A[AC][TC]-3', designated as the secondary wall MYB-responsive element (SMRE). Regulates directly numerous transcription factors and a number of genes involved in secondary wall biosynthesis that contain SMRE elements in their promoters (PubMed:22197883). Expressed specifically in fiber and vessel cells that are undergoing secondary wall thickening in floral stems. Expressed in vessels but not in xylary fibers in the developing secondary xylem of roots. No visible phenotype under normal growth conditions, but the double mutant plants myb48 and myb83 nearly lack secondary wall thickening, stop growing after developing one to two pairs of small leaves and subsequently die. Extended C-terminus.