Transcriptomics Reveals the Effect of Freezing on Signal Transduction and Galactose Metabolism of Sugar Beet

Freezing temperatures severely restrict plant growth and can cause serious damage or death to sugar beet seedlings in early spring. In this study, seedlings of two sugar beet genotypes, KWS1197 (K, freezing-tolerant) and SX1512 (S, freezing-sensitive), were subjected to RNA sequencing (RNA-seq) after exposure to −4 °C for 0, 1, 3, and 5 h. GO and KEGG enrichment and expression pattern analyses were performed to identify differentially expressed genes (DEGs) associated with freezing stress. The results showed that plant hormone signal transduction and the MAPK signaling pathway were the primary pathways involved in the freezing response in both genotypes. Notably, the galactose metabolism pathway may play an important role in freezing tolerance in KWS1197. Genes involved in galactose metabolism, including inositol 3-α-galactosyltransferase (GolS), raffinose synthase (RafS), invertase (INV), and α-galactosidase (GLA), were significantly up-regulated under freezing conditions, as confirmed by both RNA-seq and RT-qPCR analyses. These results suggest that rapid regulation of soluble sugar synthesis may represent an important mechanism contributing to freezing tolerance in sugar beet. Overall, this study provides a molecular basis for understanding freezing tolerance in sugar beet and identifies candidate genes for improving freezing resistance.