Abstract
Angiosperm gametophytes are generated from germ-line cells established from somatic-line cells in the final phase of the plant life cycle. During the course of the study on the meristem disorganization1 (mdo1) mutation, affecting the genome maintenance, we found a quite intriguing phenomenon. While the mdo1 homozygous seeds generated from mdo1 heterozygotes germinated and grew normally, albeit with the morphological abnormality, almost the mdo1 homozygous seeds generated from mdo1 homozygotes did not. In other words, germination phenotype depends not on the zygotic genotype, but on the genotype of the parental sporophytes. Microscopic observations suggested that embryogenesis of the mdo1 homozygotes is affected in early stages. In contrast, any histological abnormalities in female and male gametophytes produced by the mdo1 homozygous plants were not detected. The result obtained from genetic cross excluded a possibility that the mdo1 phenotype on embryogenesis is due to the maternal effect. These results, taken together, suggested that the MDO1 gene is involved in a novel mechanism generating embryogenesis-competent gametophytes during gametogenesis in parental sporophytes.
