The maternal chromosome set is the target of the T-DNA in the in planta transformation of Arabidopsis thaliana

In planta transformation methods are now commonly used to transform Arabido psis thaliana by Agrobacterium tumefaciens. The origin of transformants obt ained by these methods has been studied by: Inoculating different floral st ages and examining gametophytic expression of an introduced beta-glucuronid ase marker gene encoding GUS. MTC observed that transformation can still oc cur after, treating flowers where embryo sacs hare reached the stage of the third division. No GUS expression was observed in embryo sacs or pollen of plants infiltrated with an Agrobacterium strain bearing a GUS gene under t he control of a gametophyte-specific promoter. To identify the genetic targ et we used an insertion mutant in which a gene essential for male gametophy tic development has been disrupted by a T-DNA bearing a Basta resistance ge ne (B-R). In this mutant the BR marker is transferred to the progeny only b y die female gametes. This mutant was retransformed with a hygromycin resis tance marker and doubly resistant plants were selected. The study of 193 pr ogeny of these transformants revealed 25 plants in which the two resistance markers were linked in coupling and only one plant where they were linked in repulsion. These results point to the chromosome set of the female gamet ophyte as the main target for the T-DNA.