# SRS2 is required for MUS81-dependent CO formation in zmm mutants

## TL;DR

This paper shows that the SRS2 helicase influences meiotic crossover patterns in Arabidopsis, shifting the balance between Class I and Class II crossovers.

## Contribution

The study reveals a novel role for SRS2 in regulating MUS81-dependent Class II crossover formation during meiosis in plants.

## Key findings

- SRS2 is dispensable for DNA repair and Rad51-dependent recombination in somatic cells.
- Absence of SRS2 increases Class I crossovers and reduces MUS81-dependent Class II crossovers during meiosis.
- SRS2 likely regulates the resolution of recombination intermediates into Class II crossovers.

## Abstract

Helicases are enzymes that use the energy derived from ATP hydrolysis to translocate along and unwind nucleic acids. Accordingly, helicases are instrumental in maintaining genomic integrity and ensuring genetic diversity. Srs2 is a multi-functional DNA helicase that dismantles Rad51 nucleofilaments and regulates DNA strand invasion to prevent excessive or inappropriate homologous recombination in yeast. Consistently, the deletion of Srs2 has significant consequences for the maintenance of genome integrity in mitotic cells. In contrast, its role in meiotic recombination remains less clear. We present here substantial evidence that SRS2 plays an important role in meiotic recombination in the model plant Arabidopsis thaliana. Arabidopsis srs2 mutants exhibit moderate defects in DNA damage-induced RAD51 focus formation, but SRS2 is dispensable for DNA repair and RAD51-dependent recombination in somatic cells. Meiotic progression and fertility appear unaffected in srs2 plants but, strikingly, the absence of SRS2 leads to increased genetic interference accompanied by increased numbers of Class I COs and a reduction in MUS81-dependent Class II COs. We propose that SRS2 plays a role in MUS81-mediated resolution of a subset of recombination intermediates into Class II CO. The absence of SRS2 would thus lead to the alternative channeling of these recombination intermediates into the Class I CO pathway, resulting in an increased proportion of Class I CO.

Helicases are enzymes that use ATP to unwind DNA. They play a crucial role in maintaining genomic stability. One such helicase, Srs2, is known to regulate homologous recombination in yeast by preventing excessive or inappropriate recombination events. While its function in mitotic cell division is well understood, its role in meiosis - the process that generates reproductive cells - remains less clear. We show here that SRS2 plays a significant role in meiotic recombination in the plant Arabidopsis thaliana. Although Arabidopsis plants lacking SRS2 do not exhibit major defects in DNA repair or fertility, they show modifications in meiotic crossover recombination patterns. Specifically, the absence of SRS2 shifts the balance between Class I and Class II crossovers, leading to an increase in Class I crossovers and a decrease in MUS81-dependent Class II crossovers. These findings provide new insights into the role of SRS2 in meiosis, suggesting that it has a role in the regulation of Class II crossover formation.