A dirigent family protein confers variation of Casparian strip thickness and salt tolerance in maize

Plant salt-stress response involves complex physiological processes. Previous studies have shown that some factors promote salt tolerance only under high transpiring condition, thus mediating transpiration-dependent salt tolerance (TDST). However, the mechanism underlying crop TDST remains largely unknown. Here, we report that ZmSTL1 (Salt-Tolerant Locus 1) confers natural variation of TDST in maize. ZmSTL1 encodes a dirigent protein (termed ZmESBL) localized to the Casparian strip (CS) domain. Mutants lacking ZmESBL display impaired lignin deposition at endodermal CS domain which leads to a defective CS barrier. Under salt condition, mutation of ZmESBL increases the apoplastic transport of Na+ across the endodermis, and then increases the root-to-shoot delivery of Na+ via transpiration flow, thereby leading to a transpiration-dependent salt hypersensitivity. Moreover, we show that the ortholog of ZmESBL also mediates CS development and TDST in Arabidopsis. Our study suggests that modification of CS barrier may provide an approach for developing salt-tolerant crops. Most crops are farmed under high transpiring environments, but our understanding of transpiration-dependent salt tolerance (TDST) remains limited. Here, the authors report a dirigent family protein is responsible for TDST by affecting lignin deposition at Casparian strip barrier and transportation of Na+ across the endodermis.

Automated summary

The study reveals that ZmSTL1 plays a crucial role in conferring salt tolerance in maize by affecting lignin deposition and Na+ transport. The findings suggest that modifying the Casparian strip barrier could be a potential approach for developing salt-tolerant crops.