Integrated physio-biochemical and transcriptomic analysis reveals mechanism underlying salt tolerance in walnut

Walnut, an essential oilseed tree, is widely cultivated in regions such as Xinjiang, China. However, extensive saline-alkali land has significantly reduced the walnut field. Consequently, breeding salt-tolerant walnut rootstocks is crucial to development of industry. In this study, two walnut varieties (Cd and Xw) were subjected to NaCl salinity (0, 50, 100, 150 mM) to investigate physiological and molecular mechanisms of salt stress resistance. Our results revealed that salinity stress reduced growth parameters (shoot biomass, root biomass, relative ground and height growth) and photosynthetic pigments (Pn, Tr, and Cond) in both Cd and Xw compared to control plants. Additionally,as stress duration increased, proline content and antioxidant enzyme activity decreased. Transcriptomic analysis identified 9077 differentially expressed genes (DEGs), with Gene Ontology(GO) analyses indicating their involvement in hormone signaling, photosynthesis, light harvesting, and photosystems (I and II). WGCNA analysis identified hub genes highly associated with salt response, focusing on the light-harvesting chlorophyll protein complex (JrLHCb5, JrLHCa), MAPK signaling pathway (JrSAPK2), and hormone signaling processes (JrPYL4, JrSCL13). This study provides scientific evidence for further exploration of physiological and molecular mechanisms of salt tolerance in walnuts.