Loss of copy number and expression of transgene during meiosis in Pyropia tenera

Pyropia is a genus of red algae that is cultivated as a commercial food and is a model organism in marine biotechnology. Its habitat is threatened by global climate change, resulting in considerable interest in developing productive strains that are tolerant to the changing climate. Such strains will be valuable only if they are genetically stable, but introduced genetic traits often are either weakened or completely lost in progeny. To determine and understand the likely fate of a newly acquired trait in Pyropia, we generated PyGUS transgenic P. tenera and analyzed the expression of the transgene and its copy number through its sexual life cycle. The vegetative and diploid cells of parent lines showed stable expression of the PyGUS gene, but approximately 30% of progeny had no histochemical staining for GUS and reduced levels of PyGUS mRNA, even though the transgene was present. Genomic qPCR analysis revealed that the copy number of the PyGUS gene was reduced in gametophyte thalli, which were generated after meiosis. We conclude that the PyGUS gene was markedly unstable during meiosis, and that loss of gene copies and the altered expression of the transgene occurred mostly during meiotic recombination. We anticipate that these results will benefit understanding of molecular mechanisms that confer stability to genetic traits in P. tenera and related species.