Investigating Synaptonemal Complex Morphogenesis in Polyploid Wheat

The synaptonemal complex is a tripartite proteinaceous structure consisting of two filamentous lateral elements, joined by zipper-like transverse filaments and central elements that assemble to join homologous chromosomes and ensure recombination by formation of crossovers during meiotic prophase I. In polyploid wheat, components of the synaptonemal complex and its installation process are still elusive. The application of several distinct methodologies, such as Sanger sequencing, cloning and bioinformatics was conducted to analyse gene expression contribution and transcript variants for the Triticum aestivum ASYNAPTIC 1 (ASY1) and ZYPPER-LIKE 1 (ZYP1) genes. Mutant TILLING lines provided a valid strategy to functionally analyse asy1 and zyp1 and to characterize putative meiotic genes in polyploid wheat, identified via a computational screening.

Molecular analysis demonstrated a balanced expression level among the ASY1 and ZYP1 sub-genomes of hexaploid wheat, being also expressed in non-meiotic tissues, and uncovered the presence of de-novo transcript isoforms within their 3’ UTRs. Cytological analysis revealed that ASY1 is involved in chromosome homology search, since asy1 hypomorphic mutants showed multivalent associations, and is required for formation of the obligate crossover, mirroring the ph1 phenotype. Preliminary data of zyp1 single knockouts suggested a conserved role of ZYP1 in mantaining obligate crossovers, and in controlling the timing of synaptonemal complex assembly in tetraploid wheat. Furthermore, a wheat SWITCH1 (SWI1) orthologue was identified using co-expression bioinformatics tools. Lastly, a method to implement FISH-based single copy oligo-probes to discriminate individual wheat chromosomes was developed. This work provides advanced directions for studying meiosis in polyploid wheat, expanding the opportunities to manipulate crossovers and introgress agronomically important genes.