Complex haploinsufficient interaction between APC11 and CYCLIN A1;2/TARDY ASYNCHRONOUS MEIOSIS in embryo development and seed germination in Arabidopsis

Background: Complex haploinsufficiency is characterized by individuals with two heterozygous loci producing a phenotype that is not seen in either of the corresponding single-locus heterozygous individuals. The mutants of the anaphase-promoting complex/cyclosome (APC/C) subunit gene APC11 and the mitotic cyclin gene CYCLIN A1;2 / TARDY ASYNCHRONOUS MEIOSIS ( TAM ) in Arabidopsis thaliana are embryo-lethal and defective in meiosis, respectively, but their heterozygous single mutants do not exhibit defective embryo development and seed germination. Methods: Crosses between two heterozygous apc11 mutant alleles and two homozygous tam mutant alleles, and between two heterozygous apc11 mutant alleles and a TAM:TAM-GFP line were conducted. Phenotypes of the F 1 seeds were analyzed by light microscopy. Results: We found that F 1 embryos from the crosses between heterozygous apc11-1 ( APC11/apc11-1 ) and homozygous tam-2 (tam-2 / tam-2 ) or between APC11 / apc11-2 and tam-2 / tam-2 were morphologically normal but all the seeds failed to germinate. F 1 embryos from the crosses between APC11 / apc11-2 and tam-1 / tam-1 (weaker allele than tam-2 ) produced morphologically normal seeds that germinated to form mature plants. However, F 1 embryos from the crosses between APC11/apc11-1 and tam-1 / tam-1 were abnormal and the seeds failed to germinate. Moreover, F 1 embryos from the crosses between APC11/apc11-1 and a TAM:TAM-GFP line were arrested at early developmental stages while F 1 embryos from the crosses between APC11 / apc11-2 and the TAM:TAM-GFP line appeared fully developed but the seeds failed to germinate. Conclusions: Our observations indicate that the apc11 and tam mutants have an allele-dependent complex haploinsufficient relationship in embryo development and seed germination.