Mu Element-Generated Gene Conversions in Maize Attenuate the Dominant Knotted Phenotype

Abstract

The knotted1 gene was first defined by dominant mutations that affect leaf morphology. The original allele, Kn1-O, results from a 17-kb tandem duplication. Mutator (Mu) insertions near the junction of the two repeats suppress the leaf phenotype to different degrees depending on the position of the insertion. The Mu insertions also increase the frequency of recombination at Kn1-O to create derivative alleles in which the Mu element and one copy of the repeat are lost. These derivatives are normal in appearance. Here we describe two derivatives that retained the tandem duplication but gained insertions of 1.7 and 3 kb in length in place of the Mu element. In each case, the inserted DNA is a sequence that normally flanks the distal repeat unit. Thus, each derivative consists of a tandem duplication in which the repeat unit has been extended at its distal end by the length of the new insertion. The 1.7-kb insertion dampens the phenotype, as did the original Mu insertion, whereas the 3-kb insertion completely suppresses the knotted phenotype. We propose that gene conversion, stimulated by the double-strand break of the Mu excision, gave rise to these derivatives.

Meiotic recombination profiling of interspecific hybrid F1 tomato pollen by linked read sequencing

“…Interestingly, interrupted GC was shown to generate truncated Mu elements in maize. The interruption was proposed to result from hybridizing direct repeats, upon which the gap resolution would lead to a deletion (Mathern and Hake, 1997). In our data we occasionally detected GCs associated with small deletions in recombinant molecules overlapping transposon related repeats.…”

“…Furthermore, the involvement of tomato transposable elements as drivers of meiotic recombination cannot be ruled out, since we observed putative GC in recombinant molecules overlapping with repeats and transposon copies. Previously, meiotic recombination and GC induced by the Mutator (Mu) transposon in maize, resulted in deletions affecting gene function of the knotted 1 gene (Mathern and Hake, 1997). A study on the trans-acting regulatory MuDR transposon revealed increasing GC and intragenic meiotic recombination in the vicinity of a nonautonomous Mu transposon (Yandeau-Nelson et al, 2005).…”

Independent evolution of transposase and TIRs facilitated by recombination between Mutator transposons from divergent clades in maize

“…This targeting tendency for Mu elements leads to frequent insertions in the 5′-untranslated region (UTR) and upstream regulatory sequences of genes where they can alter expression without disrupting coding sequences ( 13 , 14 , 44 ). Mu insertions in or near genes can have diverse effects, including increased or decreased gene expression ( 22 , 45 ) along with increased rates of recombination and gene conversion ( 46 , 47 ). These impacts contrast with the highly abundant retrotransposons, which do not preferentially target genic regions and appear to be recombinationally inert ( 48 – 50 ).…”

Meiotic recombination in natural and experimental plant populations

“…Furthermore, the involvement of tomato transposable elements as drivers of meiotic recombination cannot be ruled out, since we observed putative GC in recombinant molecules overlapping with repeats and transposon copies. Previously, meiotic recombination and GC induced by the Mutator (Mu) transposon in maize, resulted in deletions affecting gene function of the knotted 1 gene (Mathern and Hake, 1997). A study on the trans-acting regulatory MuDR transposon revealed increasing GC and intragenic meiotic recombination in the vicinity of a nonautonomous Mu transposon (Yandeau-Nelson et al, 2005).…”