Abstract
BACKGROUND: Global warming intensifies climate extremes, with rising temperatures and more frequent heatwaves. This situation may make it more difficult for species in high-temperature regions, such as the Cycas panzhihuaensis. Introduction and domestication are vital for conservation, but low temperatures limit the spread of tropical and subtropical plants to higher latitudes and altitudes. Phytohormones mediate cold adaptation through complex signaling networks that regulate physiological and molecular responses. However, the hormonal regulation and molecular mechanisms underlying freezing tolerance in C. panzhihuaensis remain poorly understood. RESULTS: This study used C. panzhihuaensis as the research subject. We exposed the plant to freezing stress and measures leaf hormone levels under CK (control group), F1(-5 °C for 1.5 h), and F2(-5 °C for 6 h). Additionally, we conducted transcriptomic analysis to explore gene expression differences in plant hormone signal transduction pathways. The findings indicated that with prolonged freezing treatment, the contents of cis-12-oxophytodienoic acid (cis-OPDA), gibberellin A4 (GA4), and salicylic acid (SA) initially increased significantly but subsequently decreased markedly. After F2 treatment, abscisic acid (ABA) levels significantly decreased, whereas castasterone (CS), 1-aminocyclopropanecarboxylic acid (ACC), and cytokinin (CTK) exhibited notable increases. Through transcriptomic analysis, a total of 4,036 differentially expressed genes (DEGs) associated with freezing stress were identified. In the plant hormone signal transduction pathway, 69 DEGs were enriched as determined by KEGG enrichment analysis. Further analysis indicated that the altered gene expression in this pathway was closely associated with hormonal level variations and the freezing resistance of C. panzhihuaensis. This research offers essential understanding of the molecular processes behind the freezing resistance of C. panzhihuaensis and provides theoretical advice for its introduction and cultivation. CONCLUSIONS: This study revealed that C. panzhihuaensis adapted to freezing stress through dynamic hormonal regulation and transcriptional reprogramming. Key phytohormones (cis-OPDA, GA4, SA, ABA, ACC, CS, and CTK) exhibited stage-specific accumulation patterns, and the plant hormone signal transduction pathway may be involved in regulating the cold resistance mechanism in C. panzhihuaensis. These findings provide crucial insights into cold resistance mechanisms of C. panzhihuaensis and establish a preliminary theoretical foundation for introducing this species to higher latitudes.