Discovery of a novel meiotic E3 ubiquitin ligase by characterisation of the barley desynaptic mutant DES12.W

  • Sybille Ursula Mittmann

Student thesis: Doctoral ThesisDoctor of Philosophy

Abstract

Economically important cereals, such as barley and wheat, have been shown to have a skewed distribution of meiotic crossovers towards the telomeric ends of the chromosomes. We, and others, hypothesise that this must affect breeding progress because natural variation in interstitially located genes cannot be easily accessed. In order to better understand this skewed distribution of crossing over, and gain more knowledge about meiosis and recombination in cereals crops, the barley desynaptic mutant des12.w was fine mapped, identified and characterised. The des12.w allele is a spontaneous mutation, causing severe semi-sterility. It is characterised by an abnormal synaptonemal complex during prophase I leading to improper chromosome segregation due to ‘sticky’ chromosomes causing chromosomal bridges and fragments. Immunocolocalisation experiments showed this to be a result of distal chromosomal entanglements appearing at the telomere bouquet initiation stage that also cause the formation of a novel ZYP1 polycomplex-like structure. The entanglements cannot be resolved throughout meiosis as indicated by abnormal anaphase II bridges. This indicates problems with DNA break repair which is visible as extended Topoisomerase 2a foci that are usually responsible for removing entanglements. Using a large F2 population derived from a cross between near-isogenic line (NIL) BW233(des12.w) and cv. Barke, des12.w was fine mapped to a sub-centiMorgan region on chromosome 7HL. Sequencing the 10 genes contained in this region revealed a one basepair insertion in an 8bp microsatellite in an unannotated RING zinc finger gene (from here on referred to as STicky Telomere Polycomplex 1 (STTP1). In-vitro ubiquitination assays and phylogenetic analyses revealed that STTP1 is a cereal-specific E3 ubiquitin ligase. Cytological analysis indicated that loss of STTP1 causes a loss of recombination, but a detailed recombination assay exposed that there is, on the contrary, a significant increase in recombination towards the distal chromosome arms in des12.w. The increase in distal recombination could be used to improve mapping of the distal chromosome arms and for breeding to break existing linkages as well as create interesting new allele assortments. Overall this is an exciting finding as the discovery of this novel E3 ligase could lead to understanding what skews barley crossovers towards the telomeric ends.
Date of Award2017
Original languageEnglish
SponsorsThe James Hutton Institute
SupervisorRobbie Waugh (Supervisor), Isabelle Colas (Supervisor) & Luke Ramsay (Supervisor)

Keywords

  • Meiosis
  • Barley
  • Recombination
  • Fine mapping

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