Molecular Mechanisms of Growth and Salt Tolerance in Diverse Rice Cultivars Balanced by Rhodobium marinum RH-AZ.

Salt stress severely limits rice productivity, and plant-microbial interaction offer a sustainable solution. This study investigated the molecular mechanisms by which Rhodobium marinum RH-AZ treatment enhances salt tolerance in salt-sensitive cultivar 9311 and moderately salt-tolerant cultivar 3931 rice cultivars. An integrated transcriptomic and physiological analysis revealed that RH-AZ treatment significantly alleviated salt-induced growth inhibition and oxidative damage in both cultivars. Crucially, the regulatory mechanisms exhibited distinct cultivar-dependent patterns. In the moderately tolerant cultivar 3931, RH-AZ treatment mobilized a broader array of stress-responsive genes and optimized the trade-off between growth and defense by modulating the IAA/ABA balance and fine-tuning JA/SA signaling. In contrast, the salt-sensitive cultivar 9311 showed a more limited transcriptional response with less effective hormonal regulation. Furthermore, Weighted Gene Co-expression Network Analysis (WGCNA) identified a core module associated with diterpenoid biosynthesis as a key conserved pathway enhanced by RH-AZ traetment. Collectively, these findings suggest that RH-AZ treatment enhances rice salt stress adaptation by integrating basal defense potentiation, hormonal homeostasis fine-tuning, and secondary metabolism activation, with the moderately tolerant cultivar 3931 possessing a superior genetic plasticity to leverage these microbial stimuli.