Transcription activator of genes involved in biosynthesis of secondary walls. Together with NST2 and NST3, required for the secondary cell wall thickening of sclerenchymatous fibers, secondary xylem (tracheary elements), and of the anther endocethium, which is necessary for anther dehiscence. May also regulate the secondary cell wall lignification of other tissues. Expressed in various aboveground tissues undergoing thickening of the lignified secondary wall such as anthers, filaments of stamens, the base of carpels, styles, the boundaries between siliques and pedicels, the midrib of leaf veins, and inflorescence stems, specifically in interfascicular fibers (sclerenchyma), cells differentiating into vascular vessels, and xylary fibers (secondary xylem). The NAC domain includes a DNA-binding domain and a dimerization domain.