HCR1 restricts the number of meiotic crossovers in Arabidopsis

Abstract

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, consistent with a major effect on Class I repair. Yeast two-hybrid and in planta assays demonstrate interaction between HCR1 and Class I proteins, including HEI10, PTD, and MSH5. We propose that HCR1 acts in opposition to pro-recombination kinases to limit crossover numbers in Arabidopsis.