Generation of a homozygous fertilization-defective gcs1 mutant by heat-inducible removal of a rescue gene.

Key message: New gametic homozygous mutants. In angiosperms, a haploid male gamete (sperm cell) fuses with a haploid female gamete (egg cell) during fertilization to form a zygote carrying paternally and maternally derived chromosomes. Several fertilization-defective mutants in Arabidopsis thaliana, including a generative cell-specific 1 (gcs1)/hapless 2 mutant, the sperm cells of which are unable to fuse with female gametes, can only be maintained as heterozygous lines due to the infertile male or female gametes. Here, we report successful generation of a gcs1 homozygous mutant by heat-inducible removal of the GCS1 transgene. Using the gcs1 homozygous mutant as male, the defect in gamete fusion was observed with great frequency; in our direct observation by semi-in vivo fertilization assay using ovules, 100 % of discharged sperm cells in culture failed to show gamete fusion. More than 70 % of ovules in the pistil received a second pollen tube as attempted fertilization recovery. Moreover, gcs1 mutant sperm cells could fertilize female gametes at a low frequency in the pistil. This strategy to generate homozygous fertilization-defective mutants will facilitate novel approaches in plant reproduction research.