TRA1: a locus responsible for controllingAgrobacterium-mediated transformability in barley

AbstractIn barley (Hordeum vulgareL.),Agrobacterium-mediated transformation efficiency is highly dependent on genotype with very few cultivars being amenable to transformation. Golden Promise is the cultivar most widely used for barley transformation and developing embryos are the most common donor tissue. We tested whether barley mutants with abnormally large embryos were more or less amenable to transformation and discovered that mutant M1460 had a transformation efficiencies similar to that of Golden Promise. The large-embryo phenotype of M1460 is due to mutation at theLYS3locus. There are three other barley lines with independent mutations at the sameLYS3locus, and one of these, Risø1508 has an identical missense mutation to that in M1460. However, none of thelys3mutants except M1460 were transformable showing that the locus responsible for transformation efficiency,TRA1, was notLYS3but another locus unique to M1460. To identifyTRA1, we generated a mapping population by crossing M1460 to the cultivar Optic, which is recalcitrant to transformation. After four rounds of backcrossing to Optic, plants were genotyped and their progeny were tested for transformability. Some of the progeny lines were transformable at high efficiencies similar to those seen for the parent M1460 and some were not transformable, like Optic. A region on chromosome 2H inherited from M1460 is present in transformable lines only. We propose that one of the 225 genes in this region isTRA1.