SlCAX3 drives the formation of crystal idioblasts for tomato ion compartmentalization under salt stress

This cell fate transition is orchestrated by enhanced cell wall remodeling and intensive microenvironmental crosstalk. Genetic analyses establish that the vacuolar transporter SlCAX3 is essential for CI formation. Sequence and structural evaluations indicate that SlCAX3 evolutionarily lost its conserved autoinhibitory N-terminal domain, a structural specialization that may support high-flux ion transport.

Although SlCAX3-driven CI formation does not reduce total foliar Na⁺ content, it facilitates localized ion sequestration within CI vacuoles, which is associated with mitigated oxidative damage and cytotoxicity in adjacent photosynthetic tissues. This study demonstrates that tissue-level salt adaptation in tomato involves spatially coordinated transcriptional responses and localized biomineralization. The identification of SlCAX3's atypical architecture provides a functional supplement to the conserved CAX1/3 transport system in land plants.

Our findings highlight localized cell-state transitions and ion sequestration as an effective tissue-level strategy for mitigating salt stress, offering strategic genetic targets for breeding climate-resilient crops.