Integrated transcriptomics and metabolomics elucidate how arbuscular mycorrhizal fungi alleviate drought stress in Juglans sigillata.

Walnut (Juglans sigillata), an economically significant ecotype of the Juglans genus in the Juglandaceae family, is cultivated mainly in southwest China, a region prone to seasonal drought. Drought significantly reduced both the yield and quality of walnuts in this area. Arbuscular mycorrhizal fungi (AMF) are symbiotic fungi that colonize plant roots and play crucial roles in enhancing plant drought resistance. This study investigated the effects of AMF on the alleviation of drought stress. Compared to non-inoculated drought-stressed plants, AMF inoculation improved plant growth, increased photosynthetic capacity, enhanced reactive oxygen species (ROS) scavenging ability, and significantly activities of superoxide Dismutase, peroxidase, and catalase were significantly increased by 19.90 %, 18.43 %, and 8.39 %, respectively. malondialdehyde, Superoxide anion, and Hydrogen peroxide levels decreased by 18.39 %, 20.75 %, and 21.44 %, respectively, and soluble sugar and proline concentrations also significantly increased (P < 0.05), helping to maintain the osmotic balance. In addition, transcriptome results showed that ATP-binding cassette transporter related to drought resistance were significantly enriched in plants inoculated with AMF, and genes related to growth, such as IAA and CKT synthesis, transcription factors (BZIP, WRKY, and GTE), and related antioxidant enzymes. The mitogen-activated protein kinases pathway-related genes were upregulated in the inoculated drought treatment group, whereas pinobanksin and homoeriodictyol were upregulated in the inoculated drought treatment group, both of which provide support for drought resistance. In summary, AMF alleviated drought stress and promoted Juglans sigillata growth by modulating key physiological, biochemical, and molecular mechanisms involved in drought resistance. This study offers important theoretical insights that support the application of AMF in sustainable agricultural practices.