Arbuscular Mycorrhiza Induce the Regulation of Ca²⁺, ROS, and SOS Pathways Under Salt Stress in Tomato Roots

Tomato (Solanum lycopersicum L.) is a globally important horticultural crop, but its growth and productivity are limited by soil salinity. Arbuscular mycorrhizal fungi (AMF) are known to enhance salt tolerance in tomato, yet the underlying molecular mechanisms remain unclear. To explore this, we analysed the transcriptional response of non-mycorrhizal and AMF-inoculated tomato roots under salt stress. AMF-inoculated roots showed altered regulation of genes involved in Ca²⁺ signalling and salt-stress sensing, including SlMOCA1 and components of the salt overly sensitive pathway such as SlSOS3, SlTFT, and SlGI. AMF also promoted ion homeostasis by altering the regulation of K⁺ transporters and SlNHX genes encoding vacuolar H⁺/Na⁺ exchangers, contributing to improved Na⁺/K⁺ ratios. Additionally, AMF enhanced the expression of genes involved in reactive oxygen species detoxification, including catalases and ascorbate peroxidases. These findings indicate that AMF inoculation supports salt-stress tolerance in tomato roots through improved stress sensing, ion regulation, and antioxidant responses. This study provides new insights into the complex molecular interactions between tomato roots and AMF under salt stress, offering potential targets for breeding or gene-editing strategies to improve crop resilience.