Agrobacterium-mediated transformation of the temperate grass Brachypodium distachyon (genotype Bd21) for T-DNA insertional mutagenesis

Brachypodium distachyon is a promising model system for the structural and functional genomics of temperate grasses because of its physical, genetic and genome attributes. The sequencing of the inbred line Bd21 ( http://www.brachypodium.org ) started in 2007. However, a transformation method remains to be developed for the community standard line Bd21. In this article, a facile, efficient and rapid transformation system for Bd21 is described using Agrobacterium -mediated transformation of compact embryogenic calli (CEC) derived from immature embryos. Key features of this system include: (i) the use of the green fluorescent protein (GFP) associated with hygromycin selection for rapid identification of transgenic calli and plants; (ii) the desiccation of CEC after inoculation with Agrobacterium ; (iii) the utilization of Bd21 plants regenerated from tissue culture as a source of immature embryos; (iv) the control of the duration of the selection process; and (v) the supplementation of culture media with CuSO₄ prior to and during the regeneration of transgenic plants. Approximately 17% of CEC produced transgenic plants, enabling the generation of hundreds of T-DNA insertion lines per experiment. GFP expression was observed in primary transformed Bd21 plants (T₀) and their progeny (T₁). The Mendelian inheritance of the transgenes was confirmed. An adaptor-anchor strategy was developed for efficient retrieval of flanking sequence tags (FSTs) of T-DNA inserts, and the resulting sequences are available in public databases. The production of T-DNA insertion lines and the retrieval of associated FSTs reported here for the reference inbred line Bd21 will facilitate large-scale functional genomics research in this model system.