Transcription factor that acts redundantly with NAC20 to regulate the expression of genes involved in the biosynthesis of starch and storage proteins in grain. Directly binds to the promoters of starch synthase 1 (SS1), pullulanase (PUL), glutelin A1 (GLUA1), glutelins B4 and B5 (GLUB4 and GLUB5), alpha-globulin and 16 kDa prolamin, and activates their expression (By similarity). Possesses transactivation activity in yeast (PubMed:27872632). Forms homodimers (PubMed:32989010). Forms heterodimers with NAC20 (PubMed:27872632, PubMed:32989010). Forms heterodimers with NAC23 (PubMed:27872632). Expressed in developing seeds. The NAC domain includes a DNA binding domain and a dimerization domain.