Abstract: A method of controlling a genetically-modified plant or plant cells, said method comprising the following steps: (a) providing a genetically-modified plant or plant cells, said plant or plant cells containing a heterologous nucleic add encoding a first polypeptide containing or consisting of a first fragment of a protein, (b) introducing a second polypeptide into cells of said genetically-modified plant or plant cells, said second polypeptide containing (i) a second fragment of said protein and (ii) a peptide sequence enabling the introduction of said second polypeptide into cells of said genetically-modified plant or plant cells, whereby said first fragment and said second fragment jointly generate a predetermined function of said protein only when jointly present.