Exogenous spermidine (Spd) improves the tolerance to alkaline-salt stress in potato

Potato (Solanum tuberosum L.) is the world's fourth most important staple crop, but its production is increasingly threatened by soil salinization, particularly alkaline-salt stress caused by excessive NaHCO₃. Although exogenous spermidine (Spd) has been reported to alleviate abiotic stresses in various plants, its physiological and molecular mechanisms in conferring alkaline-salt tolerance in potato remain largely unknown.

The results demonstrated that exogenous Spd enhances alkaline-salt tolerance in potato by increasing antioxidant enzyme activities and maintaining osmotic balance. RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA) revealed obvious tissue-specific transcriptional reprogramming in potato under Spd-combined alkaline-salt stress, with 5,968 differentially expressed genes (DEGs) identified in leaves and only 187 in roots. KEGG pathway analysis indicated that Spd mainly regulates plant hormone signal transduction, carbon metabolism and photosynthesis pathways in leaves, as well as ribosome and energy metabolism-related pathways in roots. Three candidate hub genes, StHK4, StbZIP27 and StERF106, were screened from key Spd-responsive modules. Among them, StHK4 exhibited the highest upregulation ( Log₂FC = 3.40) and positively mediates the cytokinin-ABA signaling pathway, StbZIP27 functions in bZIP-dependent regulatory pathways to promote osmotic adjustment and antioxidant defense, and StERF106 integrates ethylene signaling and reactive oxygen species (ROS) scavenging pathways. These pathways jointly improve membrane stability, maintain osmotic balance and enhance ROS-scavenging capacity, ultimately improving potato tolerance to alkaline-salt stress.

This study demonstrates that exogenous Spd enhances alkaline-salt tolerance in potato by modulating multiple physiological processes and transcriptional networks. The screened candidate hub genes (StHK4, StbZIP27, and StERF106) serve as potential pivotal regulators responsible for Spd-induced stress tolerance, providing valuable gene resources and novel mechanistic insights for understanding polyamine-mediated stress adaptation in potato.