Control of meiotic crossovers for plant breeding

Abstract

During meiosis, homologous chromosomes pair and undergo reciprocal genetic exchange, called crossover. Crossovers have a profound effect on genetic diversity and are a critical process during crop improvement, generating new allele combinations. Meiotic crossovers are tightly restricted between one and three along chromosomes in most eukaryotes, which is a main bottleneck for plant breeding. The majority of plant crossovers are dependent on class I interfering repair pathway, with a minority formed via the class II non-interfering pathway. Class II crossover is limited by three anti-recombination pathways; however, similar pathways repressing class I crossovers have not been identified. We performed a forward genetic screen in Arabidopsis using fluorescent crossover reporters to identify high crossover rate (hcr) mutants. We identified new anti-crossover factors HCR1, HCR2 and HCR3 as repressing class I crossovers. Using genetic, cytological analyses, genome wide crossover mapping and high-throughput fluorescence reporter assays we revealed that HCR1 and HCR3 restrict crossover number by controlling protein phosphorylation and protein interactions with pro-crossover factors in class I pathway while HCR2 represses transcription of HEI10 encoding a meiotic E3 ligase that promotes crossover formation in a dosage dependent manner. Our findings provide insights into how HCR anti-crossover factors limit class I interfering crossovers. In addition, genetic disruption of HCR genes will help to accelerate diverse plant breeding and mapping of desirable quantitative trait loci.