A rapid and efficient transformation protocol for the grass Brachypodium distachyon

A fast and efficient microprojectile bombardment-mediated transformation protocol is reported for the grass species Brachypodium distachyon, a proposed alternative model plant to Oryza sativa for functional genomics in grasses. Embryogenic calli derived from immature embryos were transformed by a construct containing the uidA (coding for beta-glucuronidase) and bar (coding for phosphinothricin acetyl transferase) genes, and bialaphos, a non-selective herbicide, was used as the selection agent throughout all phases of the tissue culture. Average transformation efficiencies of 5.3% were achieved, and for single bombardments transformation efficiencies of up to 14% were observed. The time frame from the bombardment of embryogenic callus to the harvesting of transgenic T1 seeds was 29 weeks and 25 weeks for the diploid and two tetraploid accessions used, respectively. Since the seed-to-seed life cycle is 19 weeks for the diploid and 15 weeks for the tetraploid accessions, our B. distachyon transformation system allows testing of both the T0 and the T1 generation as well as production of T2 seeds within 1 year.