GSK3‐mediated phosphorylation of DEK3 regulates chromatin accessibility and stress tolerance in Arabidopsis

Chromatin dynamics enable the precise control of transcriptional programmes. The balance between restricting and opening of regulatory sequences on the DNA needs to be adjusted to prevailing conditions and is fine‐tuned by chromatin remodelling proteins. DEK is an evolutionarily conserved chromatin architectural protein regulating important chromatin‐related processes. However, the molecular link between DEK‐induced chromatin reconfigurations and upstream signalling events remains unknown. Here, we show that ASKβ/AtSK31 is a salt stress‐activated glycogen synthase kinase 3 (GSK3) from Arabidopsis thaliana that phosphorylates DEK3. This specific phosphorylation alters nuclear DEK3 protein complex composition and affects nucleosome occupancy and chromatin accessibility that is translated into changes in gene expression, contributing to salt stress tolerance. These findings reveal that DEK3 phosphorylation is critical for chromatin function and cellular stress response and provide a mechanistic example of how GSK3‐based signalling is directly linked to chromatin, facilitating a transcriptional response.