During meiotic prophase I, homologous chromosomes become tightly associated with each other along their entire length by polymerization of a proteinaceous structure known as the synaptonemal complex (SC). The SC was first observed more than 65 years ago and since then has been shown to be widely conserved; however, finding its components is a difficult task in many species, notably due to the limited sequence conservation of known SC proteins. The SC has a tripartite structure, comprising two lateral elements (LE) that act as scaffolds for chromosomes, and a central region composed of ladder-like filaments formed by ZYP1 proteins stabilized by central element (CE) proteins. To date, plants have been an intriguing exception, as no plant CE proteins have been identified. We undertook a new transcriptomic screen to answer the question of whether CE proteins were part of the SC in the model plant Arabidopsis thaliana. We selected 80 genes that presented a meiotic-like expression profile and ran Alphafold2 on the candidate genes to search for small coiled coil proteins — a common structure described for CE proteins in other species. We identified two small coiled-coil proteins, SCEP1 and SCEP2, that interact with each other in yeast two-hybrid and both localize to the center of the SC. In scep1 and scep2 mutants, homologous chromosomes align but do not synapse, and no loading of another key SC protein, ZYP1, can be detected; scep1 and scep2 exhibit chromosome mis-segregation and aneuploidy in their progeny. We found orthologs of SCEP1 and SCEP2 in at least one representative species of all vascular plants except gymnosperms. These data suggest that SCEP1 and SCEP2 are the first CE proteins to be identified in plants. Preliminary results obtained on new meiotic players identified in the screen and under characterization will be presented.

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Vrielynck N, Peuch M, Durand S, Lian Q, Chambon A, Hurel A, Guérin J, Guérois R, Mercier R, Grelon M, Mézard C. 2023. SCEP1 and SCEP2 are two new components of the synaptonemal complex central element. Nat Plants. 12:2016-2030. doi: 10.1038/s41477-023-01558-y. Epub 2023 Nov 16. PMID: 37973938.