Phenotypic and Genetic Characterization of Brassinosteroid-Deficient Mutants in Barley (Hordeum vulgare L.)

Plant height and culm sturdiness are quantitative characters important for securing cereal crop yield in adverse weather conditions with strong winds and torrential rain. Brassinosteroids, a class of growth-promoting hormones, are known to regulate culm architecture and height in plants. We recently identified a unique combination of phenotypic characters, including short and sturdy straw, specific for brassinosteroid deficiency in the barley BRASSINOSTEROID-INSENSITIVE 1 (BRI1) mutant uzu1.a. Identical combinations of phenotypes (short culm, dense spike basis, erect leaves, and undulated leaf margins) were found in wild type barley grown in presence of the brassinosteroid inhibitor propiconazole. A comprehensive phenotyping screen of historic barley mutant collections identified more than 20 morphologically identical mutants in the barley complementation groups BRACHYTIC, BREVIARISTATUM and ERECTOIDES. In silico genome mapping of brassinosteroid biosynthesis and signaling genes in combination with re-sequencing of historic barley mutants, identified HvBRI1, HvBRD (BRASSINOSTEROID-6-OXIDASE), HvCPD (CONSTITUTIVE PHOTOMORPHOGENIC DWARF) and HvDIM (DIMINUTO DWARF) as major controllers of plant height and culm robustness in barley. The identified mutants represent alternatives to the widely used but highly temperature-sensitive uzu1.a allele of HvBRI1 for the development of sturdy and climate-tolerant barley cultivars.