Uzu, a barley semi-dwarf gene, suppresses plant regeneration in calli derived from immature embryos

Barley includes semi-dwarf varieties, called uzu, which are localized in parts of southwestern Japan, the southern Korea peninsula, and coastal areas of China. The uzu phenotype possesses dark green leaves and short coleoptiles, awns, and panicles. It is controlled by a single recessive gene: uzu. Uzu results from a mutation in the brassinosteroid receptor kinase gene (HvBRI1). Brassinosteroid synergistically acts with auxin on plant morphology, which is an important plant hormone for tissue culture. For this study, tissue culture traits, including callus growth and shoot regeneration capability, were examined in F₂ populations derived from crosses between normal and uzu lines, and in isogenic lines for the uzu gene. The uzu genotype shows a lower percentage of shoot regeneration than the normal genotype in F₂ populations and isogenic lines. The uzu gene negatively affects shoot regeneration. No significant differences were found in callus growth capability between uzu and normal genotypes. Uzu isogenic lines show higher sensitivity to exogenous auxin for callus initiation than normal lines, when immature embryos were incubated on media supplemented with several concentrations of 2,4-D under culture at higher temperature (25°C). Tissue culture traits of uzu might be regulated through cross-talk between brassinosteroid and auxin.