A method for producing a transformed plant cell, the method comprising the step: (i) transforming the plant cell with a genetic construct, wherein the genetic construct comprises first and second homologous recombination elements flanking a Transformation Cassette, wherein the first and second homologous recombination elements are capable of directing the integration of the Transformation Cassette into the genome of at least one plastid which is present in the plant cell, wherein the Transformation Cassette comprises: (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, wherein the Excision Cassette comprises: a first site-specific recombination element, an optional second promoter one or more nucleotide sequences encoding one or more plant-auxin biosynthetic polypeptides, wherein the plant-auxin biosynthetic polypeptides are selected from iaaH (indoleacetamide hydrolase) and iaaM (tryptophan mono-oxygenase), a second terminator element, a second site-specific recombination element, wherein the first and second site-specific recombination elements are lox sites and are capable of being recognised by a recombinase, wherein the recombinase is a Cre recombinase, preferably wherein the method additionally comprises the step: (ii) selecting for transformed plant cells on media which is lacking auxin, and/or (iii) expressing a recombinase in the plant cell, wherein the recombinase is one which recognises the first and second site-specific recombination elements. (i) transforming the plant cell with a genetic construct, wherein the genetic construct comprises first and second homologous recombination elements flanking a Transformation Cassette, wherein the first and second homologous recombination elements are capable of directing the integration of the Transformation Cassette into the genome of at least one plastid which is present in the plant cell, wherein the Transformation Cassette comprises: (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, wherein the Excision Cassette comprises: a first site-specific recombination element, an optional second promoter one or more nucleotide sequences encoding one or more plant-auxin biosynthetic polypeptides, wherein the plant-auxin biosynthetic polypeptides are selected from iaaH (indoleacetamide hydrolase) and iaaM (tryptophan mono-oxygenase), a second terminator element, a second site-specific recombination element, wherein the first and second site-specific recombination elements are lox sites and are capable of being recognised by a recombinase, wherein the recombinase is a Cre recombinase, (a) a first promoter which is operable in said plant cell, (b) an Excision Cassette, (c) one or more transgenes, (d) a first terminator element, a first site-specific recombination element, an optional second promoter one or more nucleotide sequences encoding one or more plant-auxin biosynthetic polypeptides, wherein the plant-auxin biosynthetic polypeptides are selected from iaaH (indoleacetamide hydrolase) and iaaM (tryptophan mono-oxygenase), a second terminator element, a second site-specific recombination element, (ii) selecting for transformed plant cells on media which is lacking auxin, and/or (iii) expressing a recombinase in the plant cell, wherein the recombinase is one which recognises the first and second site-specific recombination elements.