Abstract
BackgroundPairing and synapsis of homologous chromosomes is required for normal chromosome segregation and the exchange of genetic material via recombination during meiosis. Synapsis is complete at pachytene following the formation of a tri-partite proteinaceous structure known as the synaptonemal complex (SC). In yeast, HOP1 is essential for formation of the SC, and localises along chromosome axes during prophase I. Homologues in Arabidopsis (AtASY1), Brassica (BoASY1) and rice (OsPAIR2) have been isolated through analysis of mutants that display decreased fertility due to severely reduced synapsis of homologous chromosomes. Analysis of these genes has indicated that they play a similar role to HOP1 in pairing and formation of the SC through localisation to axial/lateral elements of the SC.ResultsThe full length wheat cDNA and genomic clone, TaASY1, has been isolated, sequenced and characterised. TaASY1 is located on chromosome Group 5 and the open reading frame displays significant nucleotide sequence identity to OsPAIR2 (84%) and AtASY1 (63%). Transcript and protein analysis showed that expression is largely restricted to meiotic tissue, with elevated levels during the stages of prophase I when pairing and synapsis of homologous chromosomes occur. Immunolocalisation using transmission electron microscopy showed TaASY1 interacts with chromatin that is associated with both axial elements before SC formation as well as lateral elements of formed SCs.ConclusionTaASY1 is a homologue of ScHOP1, AtASY1 and OsPAIR2 and is the first gene to be isolated from bread wheat that is involved in pairing and synapsis of homologous chromosomes.
Highlights
Pairing and synapsis of homologous chromosomes is required for normal chromosome segregation and the exchange of genetic material via recombination during meiosis
TaASY1 is a homologue of ScHOP1, AtASY1 and OsPAIR2 and is the first gene to be isolated from bread wheat that is involved in pairing and synapsis of homologous chromosomes
While low levels of expression were evident in leaf and root tips which were not detected in the tissue series northern, the results revealed significant levels of expression in anthers during the early stages of meiosis (Figure 4D), confirming the results obtained from the other two techniques used
Summary
Pairing and synapsis of homologous chromosomes is required for normal chromosome segregation and the exchange of genetic material via recombination during meiosis. Homologues in Arabidopsis (AtASY1), Brassica (BoASY1) and rice (OsPAIR2) have been isolated through analysis of mutants that display decreased fertility due to severely reduced synapsis of homologous chromosomes. Analysis of these genes has indicated that they play a similar role to HOP1 in pairing and formation of the SC through localisation to axial/lateral elements of the SC. Extensive cytological analysis of chromosome dynamics during early meiosis in normal bread wheat and mutants such as Ph1 and Ph2 (pairing homoeologous), which display reduced specificity of chromosome pairing to homologues, have provided valuable information on the control of chromosome pairing in this organism [1,2,3,4,5,6,7]. To date there are no individual proteins that have been identified and characterised from bread wheat that have been shown to have a role in homologous chromosome pairing and synapsis
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