The eIF4E-homologous protein 4EHP (nCBP) regulates thermotolerance by modulating heat-responsive mRNAs and the HSP repertoire in Arabidopsis thaliana

Translation initiation factors of the eIF4E family play a crucial role in regulating translation and the cellular metabolism of mRNAs. Research has addressed the role of canonical 4E family isoforms in development, stress response, and during viral infection. Nevertheless, the class-II eIF4E family member cap-binding protein 4EHP (nCBP), has remained poorly characterized in plant stress responses. In this study, we show that loss of 4EHP confers enhanced basal and acquired thermotolerance and causes a mild flowering delay without major root defects. Under heat stress, 4EHP-GFP re-localizes from a diffuse cytosolic pattern to cytoplasmatic foci, co-localizing with canonical stress granule (SG) markers. Transcriptomic analysis under control, acclimation and heat stress conditions reveals that 4EHP limits the accumulation of heat-responsive mRNAs, especially those encoding heat shock proteins (HSPs), which remain constitutively expressed in 4ehp-1 mutant under control and heat stress conditions. Proteomic analysis also indicates that the absence of 4EHP alters the repertoire of HSPs compared with wild type (Col-0), especially upon heat stress, without significantly impairing the recruitment of corresponding mRNAs to translationally active polysomes. Together, our results indicate that 4EHP negatively modulates the accumulation of a specific subset of heat-responsive mRNAs fine-tuning chaperone production, via heat-responsive SG regulatory pathways.