Arabidopsis HEAT SHOCK FACTOR BINDING PROTEIN is required to limit meiotic crossovers and HEI10 transcription

The number of meiotic crossovers is tightly controlled and most depend on pro‐crossover ZMM proteins, such as the E3 ligase HEI10. Despite the importance of HEI10 dosage for crossover formation, how HEI10 transcription is controlled remains unexplored. In a forward genetic screen using a fluorescent crossover reporter in Arabidopsis thaliana , we identify heat shock factor binding protein (HSBP) as a repressor of HEI10 transcription and crossover numbers. Using genome‐wide crossover mapping and cytogenetics, we show that hsbp mutations or meiotic HSBP knockdowns increase ZMM‐dependent crossovers toward the telomeres, mirroring the effects of HEI10 overexpression. Through RNA sequencing, DNA methylome, and chromatin immunoprecipitation analysis, we reveal that HSBP is required to repress HEI10 transcription by binding with heat shock factors (HSFs) at the HEI10 promoter and maintaining DNA methylation over the HEI10 5′ untranslated region. Our findings provide insights into how the temperature response regulator HSBP restricts meiotic HEI10 transcription and crossover number by attenuating HSF activity. Synopsis Plant breeders have long sought to loosen natural constraints which meiosis imposes on the transfer of genetic information. This article highlights a negative regulator of crossover; in doing so, it identifies a potential target for making meiosis more tractable. A genetic screen and subsequent characterization of high crossover rate 2 (hcr2) in Arabidopsis revealed that HCR2 encodes HEAT SHOCK FACTOR BINDING PROTEIN (HSBP) Meiotic knockdowns show that HSBP regulates a major crossover pathway HSBP represses the transcription of HEI10 , encoding a crossover‐promoting E3 ubiquitin ligase HSBP is required to maintain DNA methylation in the 5′ untranslated region of HEI10 Graphical Abstract HSBP restrains crossover number in A. thaliana by repressing the transcription of HEI10 , encoding an E3 ligase which orchestrates the progression of meiosis.