Mutations of the brassinosteroid biosynthesis gene HvDWARF5 enable balance between semi-dwarfism and maintenance of grain size in barley.

Brassinosteroids (BRs) are phytohormones which regulate various developmental processes in plants. They are exceptional phytohormones, as they do not undergo long-distance transport between plant organs. However, knowledge about the function of the enzymes that catalyse BR biosynthesis (particularly its early stages) in cereal crops remains limited. Therefore, this study identifies and analyses the function of the HvDWARF5 (HvDWF5) gene, involved in the early stage of BR biosynthesis in barley (Hordeum vulgare), an important cereal crop, using the TILLING (Targeting Induced Local Lesions IN Genomes) approach. The detailed functional analysis allowed for the identification of various mutations in different gene fragments. The influence of these mutations on plant architecture, reproduction, and yield was characterised. Moreover, effects of the missense and intron retention mutations on sequence and splicing of the HvDWF5 transcript, sequence and predicted structure of the encoded HvDWF5 enzyme, and accumulation of endogenous BR were determined. Some of the barley mutants identified in this study showed semi-dwarfism, a trait of particular importance for cereal breeding and yield. However, unlike other BR mutants in cereals, this did not negatively affect grain size or weight. It indicated that mutations in this gene allow for a balance between plant height reduction and maintenance of grain size. Thus, the results of this study provide a novel insight into the role of the HvDWF5 gene in the BR biosynthesis-dependent regulation of architecture and reproduction of the important cereal crop - barley.