Transcriptional regulation of the Arabidopsis transportome by salt stress and symbiosis with Serendipita indica

Serendipita indica , a widely studied beneficial root-colonizing fungal endophyte, promotes plant growth under saline conditions by reducing Na + accumulation in host plants, including Arabidopsis thaliana . This reduction in Na + levels likely contributes to salt detoxification, but the underlying mechanisms remain unclear. Previous studies have demonstrated that SOS1, a key Na + transporter and major determinant of salt tolerance in plants, is not involved in this reduction. To explore whether other plant transporters might participate in Na + reduction, we first characterized the full Arabidopsis transportome, with putative substrates and subcellular localizations, and performed a comprehensive transcriptomic analysis of the full set of transporter proteins. In this study, we investigated and excluded the possible contribution of HKT1, another relevant Na + transporter implicated in salt adaptation in Arabidopsis. By examining differentially expressed transporters under salt stress, we identified a subset of candidate genes potentially involved in Na + transport. Among these, we evaluated the role of CNGC10 and CNGC13 using mutant lines under both S. indica - and non-colonized conditions. Interestingly, both transporters appeared to be involved in the endophyte-induced decrease in Na + accumulation although, other, yet-unidentified transporters may also contribute to this phenomenon. • Integration of the Arabidopsis transportome with root RNA-seq data revealed transporter regulation under salt stress and Serendipita indica symbiosis. • Symbiosis markedly buffered salt-induced transcriptional reprogramming of root transporters. • CNGC10 and CNGC13 emerged as key contributors to the S. indica -mediated reduction in Na + accumulation, supported by mutant phenotyping. • Symbiotic plants exhibited coordinated regulation of Na + /K + , Ca 2+ , and other nutrient transporters under salt stress conditions. • This work provides a comprehensive framework linking transporter regulation with fungal-enhanced salt tolerance in Arabidopsis.