The overexpression of high-molecular-weight glutenin subunit Bx7 improves the dough rheological properties by altering secondary and micro-structures of wheat gluten

•This study clarified the effects of Bx7 subunit expression levels on wheat gluten.•Micro-structures of gluten at three stages during dough mixing were analysed.•Bx7OE subunit speeds up the accumulation of glutenin polymers during grain filling.•Bx7OE increases the contents of β-sheets and intermolecular β-sheets in wheat gluten.•Bx7OE gives larger protein area, and makes the micro-structure of gluten much denser.