State IIDissociationElement Formation FollowingActivatorExcision in Maize

Abstract

Active Activator (Ac) elements undergo mutations to become nonautonomous Dissociation (Ds) elements at a low frequency. To understand the mechanism of Ds formation, we have developed high-throughput genetic and molecular screens to identify these rare Ds derivatives generated from any Ac insertion in the maize genome. Using these methods we have identified 15 new Ds elements derived from Ac insertions at eight different loci. Approximately half of the Ds elements contain filler DNA inserted at the deletion junction that is derived from sequences within or adjacent to Ac. In contrast to previous reports, several of these Ds elements lack direct repeats flanking the deletion junctions and filler DNA in the donor Ac. To accommodate our findings and those of others, we propose a model of slip mispairing during error-prone repair synthesis to explain the formation of state II Ds elements in maize. We discuss the use of these lines and molecular techniques developed here to capture somatic Ds transposition events in two-component Ac/Ds tagging programs in maize.

Spatial Configuration of Transposable ElementAcTermini Affects Their Ability to Induce Chromosomal Breakage in Maize

“…In the presence of Ac, chromosome-breaking Ds elements (Ds, state I) can convert to a different state (Ds, state II) that rarely causes chromosome breakage (McClintock, 1949). State II Ds elements have been cloned from a number of loci; sequence analysis revealed that many of these were internally deleted versions of Ac (Weil et al, 1992;Yan et al, 1999;Conrad et al, 2007). A smaller number of State I Ds elements have also been cloned; their structures include doubleDs (a state II Ds inserted into another copy of the same element in the opposite orientation; Doring et al, 1984;Weck et al, 1984) and sesquiDs (an internal deletion derivative of doubleDs; Martinez-Ferez and Dooner, 1997).…”

The Activator/Dissociation Transposable Elements Comprise a Two-Component Gene Regulatory Switch That Controls Endogenous Gene Expression in Maize

“…To eliminate TPase expression from ps1(Ac), a genetic scheme was used to recover five Ds derivatives from the Ac insertion at ps1(Ac) (Conrad et al 2007). Four of the five ps1(Ds) alleles were identified as internal deletion derivatives that do not produce functional TPase protein but retain the element at the original genomic location as the donor Ac.…”

“…One base pair of the target site duplication adjacent to this Ds insertion was also deleted. In addition to the 3563-bp deletion in ps1(Ds2), filler DNA was also present at the deletion junction, which originated from both Ac and ps1 59-UTR sequences that flanked the insertion site (Conrad et al 2007).…”

“…Line ps1(Ac), originally defined as ps1-m8TAc, was discovered through an Ac regional mutagenesis of the ps1 locus from donor site bti97156TAc as previously described . Ds insertional alleles ps1(Ds1), ps1(Ds2), ps1(Ds3), ps1(Ds4), and ps1(Ds5) were derived from ps1(Ac) through a two-step genetic selection scheme as previously described (Conrad et al 2007).…”

“…The one viable insertion allele, ps1(Ac), carries a single Ac insertion in the 59-untranslated region (UTR) 16 bp upstream of the predicted Ps1 start codon in a 39 to 59 orientation relative to Ps1 transcription ). This single insertion allele and the nonautonomous Ds deletion derivatives generated from this allele (Conrad et al 2007) are the focus of this report.…”