TaPBF1-5A promotes starch biosynthesis and regulates seed storage protein composition to increase grain weight in wheat

Grain weight is primarily determined by the accumulation of storage compounds during grain filling, and elucidation of the underlying regulatory networks will help yield improvement. In this study, we identified TaPBF1-5A, a Dof-type transcription factor, and showed that it is a key positive regulator of grain development and thousand-grain weight (TGW). Knockout of TaPBF1 caused a significant reduction in both starch content and TGW, and altered SSP composition, particularly changes in glutenin subunits and gliadin fractions. We demonstrated that TaPBF1-5A directly activates starch biosynthesis genes including SSIIa-7D , GBSSI-7D , and SBEI-7D , and regulates the key regulatory factor TaNAC019-3B . Protein interaction assays revealed that TaPBF1-5A forms a nuclear complex with TaSPA-1B, which exerts differential regulatory effects on SSP-related genes, including Glu-1By and Gli-γ-7700 . Furthermore, we identified a favourable haplotype, TaPBF1-5A-Hap1 , associated with higher TGW and present evidence of positive selection during wheat breeding. Collectively, this work reveals that TaPBF1-5A promotes wheat grain weight mainly by regulating starch biosynthesis and provides a diagnostic marker for breeding.