Transcriptional activator of genes involved in biosynthesis of secondary walls. Together with NST1, required for the secondary cell wall thickening and lignification of sclerenchymatous fibers and secondary xylem vessels (tracheary elements). Seems to repress the secondary cell wall thickening of xylary fibers. May also regulate the secondary cell wall lignification of other tissues. Binds to and activates the promoter of MYB46. Stems and roots, specifically in interfascicular fibers (sclerenchyma), cells differentiating into vascular vessels (cambium), and xylem. The NAC domain includes a DNA-binding domain and a dimerization domain.