Control of Meiotic Recombination
MAPPING TRANS-ACTING CROSSOVER MODIFIERS
One of the goal of our research is to identify trans-acting modifiers of meiotic recombination. This can be achieve in different ways, however we use two approaches to map such factors: Quantitative Trait Loci (QTL) mapping and Genome Wide Association Studies (GWAS). For both approaches we use genetic system based on segregation of fluorescent reporters, GFP and dsRED, expressed in seeds (Melamed-Bessudo et al. Plant J 2005).
Using QTL mapping, we identified a new crossover modifier, SNI1, which is a component of the cohesin/condensin-related SMC5/6 complex. The sni1 mutants exhibit a modified pattern of recombination across the genome and affects mostly noninterfering crossovers. Our study reveals the importance of the SMC5/6 complex in ensuring the proper progress of meiotic recombination in plants (Zhu et al. PNAS 2021).
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INTERHOMOLOG POLYMORPHISM AND CROSSOVER FORMATION
The initial step in crossover (CO) is double strand break (DSB) formation. However, only a small portion of DSBs will be repaired by crossover with majority being repaired by non-crossover (NCO) pathways. We seek to find how the CO/NCO decision is made and how it affects chromosomal distribution of crossover. In particular, we investigate how DNA polymorphisms affect crossover formation. Together with Ian Henderson group from Cambridge, we documented an unexpected pro-crossover role of mismatch repair factor MSH2 in regions of higher sequence diversity in Arabidopsis (Blackwell & Dluzewska et al. EMBO J 2020). We showed that the heterozygosity juxtaposition effect depends on MSH2 complexes: in mutants with impaired MSH2 interhomolog polymorphism pattern does not effect crossover formation.
The effect of DNA polymorphism on crossover formation remains not fully understood, especially at the recombination hotspot level. We developed a new approach to study hotspot activity in Arabidopsis. Using natural variation as well as Cas9-induced genome editing we found that there is no hotspot short-distance competition in A. thaliana. More interestingly, we found that crossovers occur mainly in polymorphism-free hotspot centres, however SNPs in the neighbourhood (+/-3kb) stimulate crossover activity of these hotspots. This process is fully dependent on MSH2 complexes (Szymanska-Lejman et al. Nat. Commun 2023).
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Epigenetic Regulation of Gene Expression
We also study factors that control gene expression at the chromatin level. In particular, we are interested how environmental stresses affects chromatin stage to regulate gene expression. In this respect we investigated the role of histone H2A.Z, which is a variant of H2A histone involved in the control of gene transcription. We found that H2A.Z may adopt both promoting and repressing roles in regulating gene expression, dependently on its location (Sura et al. Plant Cell 2017). At the transcription start site (TSS), H2A.Z is required for transcriptional activation of many genes, while in the gene body high levels of H2A.Z repress transcription. This may prevents unwanted expression of stress responsive genes in non-inductive conditions.
Another extensive research in our group focuses on histone acetylation, especially by histone acetyltransferase NuA4. We recently identified key components of this complex in Arabidopsis and found that by controlling both the acetylation and deposition of H2A.Z, NuA4 contributes to the switch between the stress response and autotrophic growth (Bieluszewski, Sura & Dziegielewski et al. Nat Commun 2022).
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