A method of introducing multiple expression constructs into two or more target loci of a eukaryotic cell, said method comprising. (a) transforming a population of the eukaryotic cell with one or more first constructs and one or more second constructs, wherein the eukaryotic cell comprises one or more first target loci each comprising a pair of a first recombination recognition site and a second recombination recognition site, and one or more second target loci each comprising a first fragment of a first selectable marker lacking a selectable function; wherein the one or more first constructs each comprises one or more first expression cassettes each comprising a first polynucleotide encoding a first protein of interest, wherein in each of the first constructs the one or more first expression cassettes are flanked on one side by the first recombination recognition site and on the other side by the second recombination recognition site corresponding to the same recombination recognition sites of the first target loci; and wherein the one or more second constructs each comprises one or more second expression cassettes each comprising a second polynucleotide encoding a second protein of interest, and wherein in each of the second constructs the one or more second expression cassettes are flanked on one side by a homologous region of the corresponding second target locus and on the other side by a second fragment of the first selectable marker that lacks the selectable function, wherein the second fragment comprises a sequence overlapping homologously the corresponding sequence of the first fragment of the first selectable marker of the second target loci; and (b) selecting a transformant using each of the first selectable markers wherein the first fragment and the second fragment of each of the first selectable markers undergo recombination to become functional and the homologous region of the second constructs undergo homologous recombination with the same corresponding region of the second target loci, wherein each of the second expression cassettes are integrated at the corresponding second target loci, and wherein the first and second recombination recognition sites of the first constructs undergo recombination at the corresponding first and second recombination recognition sites of the first target loci driven by at least one recombinase integrating each of the first expression cassettes at the corresponding first target loci. (a) transforming a population of the eukaryotic cell with one or more first constructs and one or more second constructs, wherein the eukaryotic cell comprises one or more first target loci each comprising a pair of a first recombination recognition site and a second recombination recognition site, and one or more second target loci each comprising a first fragment of a first selectable marker lacking a selectable function; wherein the one or more first constructs each comprises one or more first expression cassettes each comprising a first polynucleotide encoding a first protein of interest, wherein in each of the first constructs the one or more first expression cassettes are flanked on one side by the first recombination recognition site and on the other side by the second recombination recognition site corresponding to the same recombination recognition sites of the first target loci; and wherein the one or more second constructs each comprises one or more second expression cassettes each comprising a second polynucleotide encoding a second protein of interest, and wherein in each of the second constructs the one or more second expression cassettes are flanked on one side by a homologous region of the corresponding second target locus and on the other side by a second fragment of the first selectable marker that lacks the selectable function, wherein the second fragment comprises a sequence overlapping homologously the corresponding sequence of the first fragment of the first selectable marker of the second target loci; and (b) selecting a transformant using each of the first selectable markers wherein the first fragment and the second fragment of each of the first selectable markers undergo recombination to become functional and the homologous region of the second constructs undergo homologous recombination with the same corresponding region of the second target loci, wherein each of the second expression cassettes are integrated at the corresponding second target loci, and wherein the first and second recombination recognition sites of the first constructs undergo recombination at the corresponding first and second recombination recognition sites of the first target loci driven by at least one recombinase integrating each of the first expression cassettes at the corresponding first target loci.