Knocking-out the brassinosteroid biosynthesis genes DWARF1 or DWARF4 produces upright canopy architecture in wheat

The wheat dwf4 brassinosteroid biosynthesis mutation confers an erect canopy architecture without yield penalties, unlike dwf1, and is a promising target to develop ideotypes suitable for high-density planting. Brassinosteroids (BR) regulate multiple agronomic traits in plants, including leaf angle. BR depletion promotes an upright canopy architecture, which can improve vertical light distribution and grain yields in cereals under high planting densities. However, broad reductions in BR activity often negatively impact fertility and grain size. Spatially restricted modification of BR metabolism through targeting specific genes could, therefore, provide an erect canopy while minimising negative pleiotropic effects. In the BR biosynthesis pathway, DWARF1/DIMINUTO (DWF1/DIM) encodes a C-24 reductase that catalyses the production of the first committed sterol BR precursor, while DWF4 and DWF11 encode 22α-hydroxylase enzymes that act later in the pathway and exhibit partial functional redundancy. Using ethyl-methanesulphonate (EMS)-induced mutations that introduce premature stop codons, we generated wheat lines lacking functional copies of all three homoeologues of DWF1 and DWF4 in the Cadenza background. The dwf4-abd mutant displayed upright leaves and a slight height reduction but showed no differences in grain size or weight when tested in glasshouse and field conditions. The dwf1-abd mutant also produced an upright canopy, but tiller number, grain size and grain weight were reduced compared to the wild-type. The dwf1-abd mutant was hypersensitive to exogenous BR application. Metabolite profiling showed that concentrations of the BR precursors campesterol (CR), campestanol (CN) and 6-oxocampestanol (6-oxoCN) were significantly reduced in dwf1-abd seedlings compared to wild-type controls, whereas precursor levels were not reduced in dwf4-abd seedlings, consistent with gene redundancy.