HUB1 positively regulates salt tolerance in Arabidopsis through dynamic H2B monoubiquitination.

key messageHUB1 positively regulates salt tolerance in Arabidopsis by modulating H2Bub1 dynamic within the gene bodies of salt-responsive genes, thereby regulating their transcription reprogramming Soil salinity severely limits plant growth and agricultural productivity worldwide, driving plants to rely on rapid transcriptional reprogramming for stress adaptation. Histone H2B monoubiquitination (H2Bub1) is a conserved chromatin modification associated with active gene transcription. However, the role of H2Bub1 in response to salt stress remains unclear, and whether H2Bub1 occupancy work on the gene responsiveness upon salinity is obscure. Here, we demonstrate that HUB1 acts as a key positive regulator of salt tolerance. Loss of HUB1 results in pronounced salt hypersensitivity, characterized by excessive reactive oxygen species accumulation, disrupted Na⁺/K⁺ homeostasis, reduced osmolyte accumulation, and impaired growth under saline conditions, whereas overexpression HUB1 enhances salt tolerance. Transcriptome analyses reveal widespread misregulation of salt-responsive genes in hub1-7, accompanied by defects in metabolic processes, ABA- and MAPK-mediated signaling pathways. Genome-wide chromatin immunoprecipitation sequencing (ChIP-Seq) shows that salt stress induces a global redistribution of H2Bub1, with increased enrichment within gene bodies that positively correlates with transcriptional activation of salt-induced genes. Collectively, our findings establish HUB1-mediated H2Bub1 dynamics at gene bodies as an important chromatin-based mechanism for transcriptional regulation and salt stress adaptation in Arabidopsis, providing new insights into epigenetic control of plant stress responses.