Synergistic Inoculation of Funneliformis mosseae and Pseudomonas putida Enhances Drought Resilience in Citrus reticulata Through Coordinated Physiological and Transcriptomic Responses.

Climate change and increasing drought conditions significantly impede citrus productivity in subtropical and tropical regions. This study explores the potential of combining arbuscular mycorrhizal fungi (AMF) Funneliformis mosseae and plant growth-promoting rhizobacteria (PGPR) Pseudomonas putida to enhance drought tolerance in Citrus reticulata (Red tangerine). Although AMF-mediated drought tolerance has been extensively documented, the interactive effect of PGPR and AMF on phytohormone signalling, photosynthetic efficiency, nutrient acquisition, and gene expression remains largely unexplored in citrus. An experiment was conducted under well-watered and drought conditions to assess the physiological and molecular responses to individual and co-inoculation with PGPR and AMF. Under drought condition, dual inoculated plants showed significantly improved leaf water potential, stomatal conductance, carbon assimilation and antioxidant defence. PGPR-AMF co-inoculation enhanced chlorophyll stability, osmotic adjustment and nutrient uptake, while significantly reducing lipid peroxidation and ROS accumulation. The turquoise module emerged from transcriptomic and gene co-expression network analysis (WGCNA) as a potential key regulator of stress adaptation, revealing key regulatory transcription factors (e.g., CrMYB4, CrZFP8, CrSOS5, CrRGFR2 and CrQUA1) upregulated under combined inoculation, highlighting their potential role in stress adaptation. Our findings demonstrate that the synergistic PGPR-AMF interaction improves antioxidant enzyme activities and modulates gene expression to promote drought tolerance, providing new insights into the microbiome's role in plant resilience. These results offer a potential strategy to boost citrus growth and yield under water scarcity, with broad implications for agricultural resilience to climate change.