Meiotic crossover recombination—the reciprocal exchange between homologous chromosomes—is fundamental to genetic diversity and proper chromosome segregation. Crossovers are distributed non-randomly along chromosomes, and in many eukaryotes, both the physical organization of meiotic chromosomes and local chromatin states influence where recombination occurs. The authors ask whether meiotic chromosome architecture (the axis and synaptonemal complex) and DNA methylation genetically interact to control crossover placement and frequency across different chromosomal intervals in plants.
The study uses Arabidopsis thaliana as a model and combines mutations that perturb meiotic chromosome architecture with mutations that alter DNA methylation. Specifically, meiotic axis or synaptonemal complex function was disrupted by reducing ASY1 levels (asy1/+) or removing ZYP1 (zyp1). DNA methylation was altered by heterozygous met1/+ and cmt3 mutations, which reduce methylation in the CG and CHG contexts, respectively. These combinations allowed assessment of genetic interactions between structural meiotic components and epigenetic marks.
Crossovers were quantified in specific chromosomal intervals located near telomeres and centromeres using fluorescent seed–based reporter assays. These reporters provide interval-resolved readouts of recombination frequency in seeds, enabling the investigators to determine how different perturbations affect crossover rates in telomere-proximal versus centromere-proximal regions.
The analyses reveal that the meiotic chromosome axis protein (ASY1) and the synaptonemal complex component (ZYP1) can interact with DNA methylation states to control crossovers. In some chromosomal contexts these factors have distinct roles, while in others they act cooperatively. The study highlights a coordinated role for axis/SC components together with CG DNA methylation in controlling crossovers, particularly in centromere-proximal intervals.
Mutations that reduce CG methylation (met1/+) showed interactions with axis and synaptonemal complex perturbations in controlling crossovers, supporting a cooperative role for CG methylation with structural meiotic proteins. In contrast, loss of CHG methylation (cmt3) did not fully restore centromere-proximal recombination defects caused by depletion of ASY1 or ZYP1. This indicates that CHG hypomethylation alone is insufficient to compensate for loss of meiotic structural components in those intervals, emphasizing a context-dependent contribution of different DNA methylation contexts to recombination control.
A notable finding is that increasing the dosage of ASY1 promotes crossovers within the pericentromere. This result identifies a non-epigenetic route—modulating a chromosome axis protein—to upregulate recombination in regions that are typically recombination-suppressed. The observation points to the axis as a lever to modify recombination landscapes independently of DNA methylation changes.
Together, the data support a model in which meiotic chromosome architecture and DNA methylation jointly shape recombination landscapes in an interval- and context-dependent manner. CG DNA methylation appears to cooperate with axis and synaptonemal complex components to regulate centromere-proximal crossovers, whereas CHG methylation changes do not substitute for physical architecture in restoring recombination in those regions. The ability to increase pericentromeric crossovers by raising ASY1 dosage suggests potential strategies to manipulate recombination distribution for breeding or genetic studies, though practical applications would require further validation.
This work is presented as a bioRxiv preprint and has not been peer-reviewed. The summary here is based on the abstract and information provided in the preprint record. Specific experimental details, quantitative results, and statistical analyses are reported in the full preprint; those numerical outcomes are not reproduced in this summary. Further validation and peer review are needed to confirm and extend these conclusions.
The study reports that DNA methylation and meiotic chromosome architecture can act both distinctly and cooperatively to control crossover placement in Arabidopsis, with CG methylation cooperating with axis and synaptonemal complex components and increased ASY1 dosage providing a non-epigenetic mechanism to enhance pericentromeric recombination. These findings underline the interval-specific complexity of recombination control and suggest routes for modulating crossover landscapes.