Spontaneous Brassinolide-insensitive Barley Mutants ‘uzu’ Adapted to East Asia

The uzu gene shows typical semi-dwarf plant type and has resulted in lodging resistance and improved canopy structure in barley (Hordeum vulgare L.). The geographic distribution of ‘uzu’ lines is limited in East Asia including Japan, Korean peninsula and China. For many years, majority of cultivated six-rowed barley varieties in southern Japan were ‘uzu’ type. Inheritance of the uzu gene, located on chromosome 3H, is monogenic recessive and the expression is pleiotropic during developmental process. In cereal crop plants, several semi-dwarf genes have been widely used in breeding programs to increase productivity and it is known that several of these semi-dwarf genes were derived from gibberellin (GA)-related mutations. The barley dwarfing gene uzu is independent to GA. This characteristics are known earlier. In this study, we characterized uzu gene in molecular aspects. As the result of comprehensive study using several pairs of isogenic lines, we found the morphological and physiological similarities of barley uzu gene to rice dwarf mutant, d61. D61 encodes OsBRI1, which is homologous gene for Brassinosteroid insensitive 1 in Arabidopsis. We also found that ‘uzu’ lines specific single nucleotide polymorphism (SNP) contributed for amino acid substitution in barley homologous sequence of OsBRI1, HvBRI1. Linkage analysis using a segregating population for uzu showed the co-segregation between uzu and HvBRI1. Furthermore, as the results of derived cleaved amplified polymorphic sequences (dCAPS) marker analysis using more than 260 ‘uzu’ landraces and the genomic sequencing analysis of HvBRI1 gene derived from 19 barley accessions, all the ‘uzu’ lines investigated in this study had the same SNP in putative kinase domain of HvBRI1. On the basis of these findings, we discussed the phylogeny of ‘uzu’ landraces in East Asia.