ABSTRACT
The ability to transform M. truncatula via Agrobacterium tumefaciens was one of the original criteria used to select this legume as a model species (Barker et al., 1990). The Agrobacterium T-DNA transfer machinery generates simple, well-characterized insertion profiles consisting of a small number of T-DNA copies (Tinland, 1996). Conventional A. tumefaciens transformation generally comprises an initial coculture step involving T-DNA transfer to plant cells, followed by the selection and subsequent regeneration of the transformed cells. Since the limiting step is most often the in vitro regeneration of transformed cells into entire transgenic plants via organogenesis or embryogenesis, the regeneration capacity of a given genotype is of critical importance. In the case of M. truncatula, recurrent breeding for highly regenerative genotypes resulted in successful genetic transformation (Thomas et al., 1992). Since then, various improvements and alternative transformation protocols have been published and are presented in this chapter. We first detail the different techniques currently available for genetic transformation of M. truncatula using A. tumefaciens and subse-
quently describe an alternative approach using A. rhizogenes, which avoids in vitro plant regeneration. Examples are presented to illustrate the use of these different transformation techniques and we discuss how to choose the most appropriate method for a given experimental objective.
