A process of generating transgenic plants or plant cells transformed on their plastome and being devoid of a selection marker, comprising the following steps: (a) transforming plastids of a plant or plant cell with a DNA comprising: (i) a nucleotide sequence conferring replication of said DNA in a plant cell, (ii) at least one sequence of interest, (iii) sequences flanking said at least one sequence of interest necessary for stable integration of said at least one sequence of interest into the plastid genome, and (iv) a selection marker outside of said sequences flanking said sequence(s) of interest; (b) allowing integration of said at least one sequence of interest into the plastome in the presence of selective pressure; (c) allowing loss of said selection marker sequence by releasing selective pressure; and (d) recovering cells and/or plants being genetically transformed on their plastomes and being devoid of said selection marker.