Salt-responsive SSN1 condensation in nucleus facilitates PIF4 degradation to regulate Arabidopsis salt tolerance

Soil salinity is detrimental to crop yield and global food security. The most well-known adaptation strategy for plant salt tolerance is to activate the plasma membrane localized salt sensing and signaling pathway to extrude Na⁺ from cytosol to apoplast. Here, we identify Arabidopsis transcriptional repressor protein SALT SIGNALING IN NUCLEUS 1 (SSN1) forms salt bodies in the nucleus through liquid-liquid phase separation upon salt stress. As a negative regulator in salt tolerance, the rapid salt-induced SSN1 condensation in the nucleus is required for SSN1 degradation. SSN1 also co-condenses with another negative regulator PHYTOCHROME-INTERACTING FACTOR 4 (PIF4) through assembling the SALT OVERLY SENSITIVE 2 (SOS2)-PIF4 complex in the same salt body. We propose that in addition to the cell surface salt extrusion pathway, the formation of the salt body by SSN1 in the nucleus is essential for plant survival under salt stress.