NOVEL, DEVELOPMENTALLY SPECIFIC CONTROL OF DS TRANSPOSITION IN MAIZE

Plants form their gametes late in somatic development and, as a result , often pass somatic mutations on to their progeny. Classic examples o f this process are the germinal revertants of unstable, Ac/Ds transpos on-induced kernel mutations in maize: frequent and early reversion eve nts during somatic development are generally correlated with a high fr equency of revertant gametes. We have characterized a Ds allele of the maize waxy (wx) gene, wx-m5:CS7, for which the correlation between so matic and germinal reversion frequencies no longer holds. The ability of wx-m5:CS7 (CS7) to produce revertant gametes is suppressed similar to 100-fold in comparison with a second Ds allele, wx-m5:CS8 (CS8), wh ich has an identical insertion at Wx and the same frequent and early s omatic reversion pattern in endosperm. The excision of Ds from wx is n ot reduced 100-fold in the somatic tissues of CS7 plants as compared w ith CS8 plants. Suppressed formation of CS7 revertant gametes is indep endent of the Ac transposase source and is heritably passed to the emb ryos of progeny kernels; however, frequent and early somatic reversion is observed again in endosperms of these progeny kernels. This suppre ssion appears to be caused by a dominant mutation in a trans-acting pr oduct that can suppress the germinal reversion of other Ds-induced all eles as well; the mutation is tightly linked to Wx but is not in the C S7 Ds itself. Taken together, the data suggest a novel mode of develop mental control of Ac/Ds elements by the host plant, suppressing elemen t excision in the shoot meristem.