A simple <Emphasis Type="Italic">Agrobacterium tumefaciens</Emphasis>-mediated transformation method for rapid transgene expression in <Emphasis Type="Italic">Medicago truncatula</Emphasis> root hairs

Medicago truncatula is widely used as a model legume for symbiotic and pathogenic microbial interaction studies. Although a number of Agrobacterium-mediated transformation methods have been developed for M. truncatula, a rapid root transformation system was not yet available for this model plant. Here, we describe an easy method for rapid transgene expression in root hairs of M. truncatula, using young seedlings co-cultivated with the disarmed hypervirulent A. tumefaciens strain AGL1. This method leads to efficient expression of various GUS and fluorescent reporters in M. truncatula root hairs. We showed that transgene expression is detected as soon as 2 days following co-culture, in root hairs of a particular responsive zone lying 0.5–2 cm behind the root tip. This method can be used with a variety of M. truncatula genotypes, and is particularly useful for rapid investigation of the sub-cellular localization of fluorescent fusion proteins. Moreover, combining distinct Agrobacterium strains during the initial co-culture step efficiently generates co-transformed root hairs, suitable for co-localization of different fluorescent fusion proteins in the same cell.