Multi-layered apoplastic barrier underlying the ability of Na⁺ exclusion in Vigna marina.

This article focuses on the mechanisms of salt tolerance in the wild coastal legume species Vigna marina, highlighting its ability to suppress sodium (Na⁺) uptake through the formation of a multi-layered lignified apoplastic barrier around root endodermis. Comparative transcriptome and histological analyses showed that under salt stress, V. marina uniquely upregulates genes involved in Casparian strip (CS) formation and develops a thicker, multi-layered lignin barrier compared to its relative Vigna luteola, which forms only typical or spot-like CS structures. Disruption of this lignified barrier increased Na⁺ transport to shoots and caused salt damage symptoms, while essential nutrient transport (K⁺, Mg²⁺, Ca²⁺) was maintained, likely via enhanced symplastic pathways and upregulated ion transporters. The study suggests that the multi-layered lignified apoplastic barrier is a key trait for salt exclusion in V. marina and represents a promising target for improving salt tolerance in crop species through genetic approaches.