Meiotic crossovers are tightly restricted in most eukaryotes, despite an excess of initiating DNA double-strand breaks. The majority of plant crossovers are dependent on Class I interfering repair, with a minority formed via the Class II pathway. Class II repair is limited by anti-recombination pathways, however similar pathways repressing Class I crossovers are unknown. We performed a forward genetic screen in Arabidopsis using fluorescent crossover reporters, to identify mutants with increased or decreased recombination frequency. We identified
HIGH CROSSOVER RATE1
(
HCR1
) as repressing crossovers and encoding PROTEIN PHOSPHATASE X1. Genome-wide analysis showed that
hcr1
crossovers are increased in the distal chromosome arms. MLH1 foci significantly increase in
hcr1
and crossover interference decreases, demonstrating an effect on Class I repair. Consistently, yeast two-hybrid and
in planta
assays show interaction between HCR1 and Class I proteins, including HEI10, PTD, MSH5, and MLH1. We propose that HCR1 plays a major role in opposition to pro-recombination kinases to restrict crossovers in Arabidopsis.