The ESCRT component FYVE4 modulates salt-stress response by strengthening the SOS1–SOS2 interaction in Arabidopsis

The plant-specific FYVE-domain-containing protein FYVE4, a component of the endosomal sorting complex required for transport III (ESCRT-III), participates in membrane protein sorting. However, the mechanism by which FYVE4 coordinates plant growth responses to environmental stress remains unclear. In this study, we reveal a novel function of FYVE4 in positively regulating plant salt resistance by modulating the Salt Overly Sensitive (SOS) signaling pathway. FYVE4 enhances SOS1 phosphorylation by promoting SOS1-SOS2 interactions during salt stress. Loss of FYVE4 reduces the SOS1-SOS2 association, leading to decreased SOS1 phosphorylation and increased plant sensitivity to salt stress. Notably, overexpression of SOS1 does not rescue the salt-sensitive phenotype of fyve4-1, whereas SOS2 overexpression does. In summary, our findings highlight the critical role of FYVE4 in promoting SOS1-SOS2 interactions to mitigate salt stress and reveal a previously unrecognized function of FYVE4 in abiotic stress responses, extending beyond its established role in membrane trafficking regulation.