HIGH CROSSOVER RATE1 restricts the number of meiotic crossovers in Arabidopsis

Abstract

Meiotic crossover creates new combinations of genetic variation and ensures balanced chromosome transmission. Crossover numbers per meiosis are tightly restricted in most eukaryotes, despite a large excess of initiating DNA double-strand break precursors. The majority of crossovers in plants are dependent on the Class I interfering repair pathway. A minority of crossovers are formed by the Class II non-interfering pathway, which is normally limited by multiple anti-recombination pathways. However, similar pathways that limit Class I interfering crossovers are unknown. To identify regulators of crossover formation, we performed a forward genetic screen in Arabidopsis using fluorescent crossover reporters, to identify mutants with increased or decreased recombination frequency. This screen identified the HIGH CROSSOVER RATE1 (HCR1) gene as repressing crossovers. Using genome-wide analysis we show that hcr1 crossovers are most strongly increased in the distal euchromatic chromosome arms. We observe a significant increase in MLH1 foci in hcr1 and a decrease in the strength of crossover interference, which is consistent with a major effect on the Class I pathway. We used yeast two hybrid and in planta assays to demonstrate physical interaction between HCR1 and multiple proteins within the Class I interfering pathway, including HEI10, PTD, and MSH5. Our data identify HCR1 as limiting the number of interfering Class I crossovers in plants. We propose that HCR1 acts in opposition to pro-recombination DNA repair or cell division kinases, in order to limit crossover number per meiosis.