Transcription factor that acts redundantly with NAC20 to regulate the expression of genes involved in the biosynthesis of starch and storage proteins in grain (PubMed:32989010). 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 (PubMed:32989010). Forms homodimers (PubMed:32989010). Forms heterodimers with NAC20 (PubMed:27872632, PubMed:32989010). Forms heterodimers with NAC23 (PubMed:27872632). Expressed in developing seeds (PubMed:27872632). Expressed in developing endosperm (PubMed:18813954, PubMed:32989010). The NAC domain includes a DNA binding domain and a dimerization domain. No visible phenotype under normal growth conditions (PubMed:32989010). The double mutant nac20 and nac26 exhibit a floury grain phenotype due to decreased starch and storage protein content (PubMed:32989010).