In somatic cells during heat shock, HSBPs translocate from the cytosol to the nucleus to attenuate the activity of the HSF (heat shock factor) trimer. The activation‐attenuation cycle of HSF‐HSBP controls the transcription of heat shock protein genes (HSPs) and many other genes including HEI10.
In meiotic cells, during early meiosis, HSFs are highly expressed and activated by unknown developmental factors and signals, potentially including reactive oxygen species (ROS). Plant meiocytes are surrounded by multi‐layered cells and thick callose cell walls, which may induce hypoxia and ROS. Active HSFs contribute to the transcriptional induction of HEI10, in addition to many other genes. Simultaneously or subsequently, HSBP accumulates to high levels and moves to the nucleus during early meiosis. HSBP hexamers bind to HSF trimers and attenuate HSF activity, which decreases HEI10 transcription. The protein levels and activities of HSFs and HSBP are likely important for determining transcript levels of HEI10 during early meiosis.
In hsbp‐3 meiotic cells, HSBP levels are lower than in wild type during early meiosis, which leads to higher HEI10 transcripts, HEI10 protein levels, and class I crossovers. The lack of DNA methylation at the HEI10 5′ UTR contributes to the initiation of meiosis with higher HEI10 transcript levels in hsbp‐3.
