Abstract
Maintenance of undifferentiated stem cells is one of the important functions of plant apical meristems. We isolated a novel mutant, named meristem disorganization1-1 (mdo1-1), exhibiting abnormal shoot morphogenesis. The mdo1-1 homozygous plants showed pleiotrophic shoot phenotypes, such as aberrant phyllotaxis and plastochrone, and frequent stem fasciation. In the mutant apical meristems, the canonical layer structure was disrupted and undifferentiated stem cells were not properly maintained, associated with cell death and cell differentiation. The mdo1-1 mutants also showed elevated level of DNA double-strand breaks and expression of DNA damage-induced genes. These results suggest that the enhanced level of DNA damage results in the disorganized meristems in the mdo1-1. Molecular cloning as well as complementation test indicated that the MDO1 gene encodes a relatively small protein found specifically in wide variety of land plants and that, in mdo1-1, tightly conserved amino acid in the orthlogs is substituted. These results, thus, suggest that the MDO1 gene function is crucial for maintenance of undifferentiated stem cells in apical meristems.
