A co-chaperone J3 limits crossovers by facilitating proteolysis of pro-crossover factors in Arabidopsis

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Meiosis-specific E3 ligase HEI10 controls crossovers in Arabidopsis thaliana

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HCR1 restricts the number of meiotic crossovers in Arabidopsis

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.1

HCR2 limits crossovers by repressing HEI10 transcription in Arabidopsis

Meiotic crossover creates new genetic variations and is produced by the repair of programmed DSBs (DNA double strand break sites). Despite excessive meiotic DSBs, crossover number is limited along each pair of homologous chromosomes. The majority of crossovers are interfering and formed by crossover-promoting ZMM proteins including HEI10, a dosage dependent E3 ligase. However, molecular mechanisms restricting number of interfering crossovers remain unexplored. We here identified HCR2 (HIGH CROSSOVER RATE 2) via a forward genetic screen using fluorescent reporter in Arabidopsis. Using genome wide crossover mapping and fluorescent reporter systems we found that the hcr2 and meiosis specific HCR2 knockdown plants display elevated crossover frequency in chromosome arms, with reduced crossover interference. The hcr2 mutation lead to increase the transcript level of HEI10, thereby elevating crossover number. Our data reveal a novel mechanism of limiting crossovers by which HCR2 transcription regulator represses HEI10 transcription.1

HIGH CROSSOVER RATE1 encodes PROTEIN PHOSPHATASE X1 and restricts meiotic crossovers in Arabidopsis

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.1

HIGH CROSSOVER RATE1 restricts the number of meiotic crossovers in Arabidopsis

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.1