The maize LAG1-O mutant suggests that reproductive cell lineages show unique gene expression patterns early in vegetative development

Patterns of transposable element activity often provide useful information about how and when organisms regulate gene expression. The maize lowered Ac /Ds germinal reversion 1 (LAG1)-O mutation causes unusually low rates of ge rminal reversion by Ac/Ds-induced alleles even though these same alleles;ev ert frequently and early in somatic development. LAG1-O suppresses Ds trans position at multiple, unlinked loci, and does not affect Spm elements, indi cating that the mutation acts in trans and may be specific to Ac/Ds element s. Our data suggest that LAG1-O suppression gradually reduces Ac/Ds activit y in the meristem and newly formed leaves until, by the floral transition, transposition is undetectable even with PCR-based assays. This suppression persists during tassel development and does not appear to be released until some point after meiosis. Competitive RT-PCR results show no difference in Ac transposase mRNA levels between LAG1-O and lag1(+) tassels, suggesting that suppression is post-transcriptional. The pattern of LAG1-O expression is consistent with a model in which at least some gene expression specific to those meristem cells that will ultimately give rise to floral tissue and therefore gametes begins very early in plant development, and then persist s throughout development.