An unusual maize mutation, Lowered Ac/Ds Germinal reversion (LAG1-0) has been identified and partially characterized in this laboratory. It will be used to address specific questions of the regulation of the frequency of Ac/Ds transposon excision and how it is affected by the different stages of development of the plant. Ds transposon-induced alleles that revert frequently in the endosperm of the maize typically revert frequently in gametes of the plant from that kernel. But in the presence of LAG1-), these same Ds alleles revert germinally about 100-fold less often than in non-mutant lag1+ plants, while reversion in endosperm remains unchanged. LAG1-0 is tightly linked to the waxy locus on chromosome 9, is a dominant mutation in a trans-acting product and affects Ds excision regardless of Ac transposase source. The degree to which LAG1-0 suppresses Ac/Ds excision becomes more severe in somatic tissues as development progresses. Whether LAG1-0 suppression is imposed on Ac/Ds specifically in the slowly dividing cells of the meristem at the beginning of development will be tested. The specific aims are: 1) to isolate and characterize the LAG1-0 mutation, 2) to define more clearly when and where in development the suppression of Ac/Ds excision occurs, 3) to more clearly define the genetic mechanisms involved in the suppression, 4) to identify other genes and factors that regulate this unusual pattern of gene expression.
Meristems of higher plants are dome-shaped populations of actively dividing, relatively undifferentiated cells that are, ultimately, the source of all cells in the plant. How these cells become differentiated during development must be a function of regulated gene expression but it is, as yet, not understood at the molecular level. The LAG1-0 mutation characteristics suggest that an Ac or Ds element has inserted into a gene relevant to this process and this hypothesis will be tested by further experimentation. The results of this study could provide greater insight into the molecular mechanisms involved in plant development.
