Effects of exogenous calcium pretreatment on the cold resistance of Phoebe zhennan seedlings.

Phoebe zhennan is a high-quality timber tree species mainly distributed in the subtropical regions of China. It is very important to study and improve the cold resistance of P. zhennan from the mechanism and practice for expanding its introduction and cultivation range. However, there is a lack of research on the cold resistance mechanisms of Zhennan seedlings. The present study investigated the effects of exogenous Ca²⁺ on the cold resistance in Zhennan. The results showed that Ca²⁺ pretreatment increased the levels of abscisic acid, peroxidase, catalase, proline, and soluble sugar and decreased the levels of malondialdehyde and relative electrical conductivity. In addition, RNA sequencing was used to investigate the global transcriptome response to cold stress. Gene set enrichment analysis, Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis, and gene ontology analysis were used to compare the differentially expressed genes before and after calcium treatment and before and after cold stress. These analyses together with the short time sequence clustering analysis of transcriptome data and predictive protein interaction analysis showed that the transcription factors PzWRKY71, PzTAF, and PzMYB7 play key roles in the regulation of and balance between cold resistance and growth in immune system. Moreover, it was found that the mechanisms of protein phosphorylation and ubiquitin-mediated protein degradation significantly affected the calcium ion-mediated cold resistance mechanism, and there was a complex regulatory relationship between them. The results provide valuable insights into the Ca²⁺-mediated cold resistance mechanism and have potential applications for improving cold stress tolerance in Zhennan seedlings.