A HEAT-SHOCK PROMOTER FUSION TO THE AC TRANSPOSASE GENE DRIVES INDUCIBLE TRANSPOSITION OF A DS ELEMENT DURING ARABIDOPSIS EMBRYO DEVELOPMENT

A heat-shock promoter fusion to the Ac transposase gene (hs::TPase) wa s constructed and introduced into Arabidopsis. In five transformants c ontaining the fusion the abundance of transposase mRNA increased appro ximately 120-fold on exposure to high temperatures. Hybrid plants cont aining hs::TPase and a Ds element inserted in a streptomycin resistanc e gene (Ds::SPT) were made and these plants were self-fertilized eithe r after heat shocking at different stages in development or without ex posure to high temperature. The progeny of these plants were sown on s treptomycin-containing medium and the frequency with which variegated or streptomycin-resistant (strep(R)) seedlings occurred was used as an indication of the frequency of Ds excision. Very few of the progeny o f plants not exposed to heat shock or of those heat shocked only durin g vegetative development were variegated or strep(R). However, plants that were heat shocked after the appearance of flower buds and during seed development produced high frequencies (approaching 100%) of varie gated, but very few strep(R), progeny. Furthermore, when variegated se edlings were grown to maturity and self-fertilized without further exp osure to heat shock then strep(R) seedlings often occurred at high fre quency among their progeny. Southern analysis indicated that the major ity of these strep(R) plants contained a transposed Ds at a new locati on. These data indicate that in response to heat shock Ds excision fre quently occurs in embryonic cells which ultimately give rise to the ga metes, as well as in cells of the developing cotyledons. The importanc e of an inducible transposon system for transposon tagging is discusse d.