Evaluation of cold tolerance in maize diversity panel and transcriptome analysis of two extreme genotypes under cold...

Low temperature is a crucial factor limiting the growth and geographical distribution of maize. Screening cold-tolerant maize is of great significance for identifying cold tolerance-related genes and improving maize performance under low, sub-optimal temperature conditions. In the present study, a total of 205 maize genotypes with diverse genetic backgrounds to cold stress were evaluated for cold tolerance at the seedling stage under low-temperature stress. Five physiological indices (relative electrical conductivity (REC), seedling plant height (PH), root length (RL), shoot fresh weight (FW), and shoot dry weight (DW)) were used to assess cold tolerance. A comprehensive evaluation of cold tolerance based on the use of D value was conducted, in which By813 with the highest D value, was considered as the cold-resistant genotype and CML454 with the lowest D value was considered as the cold-sensitive genotype. Transcriptomic analysis revealed that the number of differentially expressed genes (DEGs) in By813 was slightly higher than in CML454. The two maize genotypes exhibited 10,682 DEGs at control temperature (28 °C, CK) and 8852 DEGs under low-temperature stress (4 °C, LT). Gene Ontology (GO) enrichment analysis of these DEGs revealed a significant enrichment of specific biological processes and molecular functions associated with ethylene synthesis, steroid metabolism, and secondary metabolism and biosynthesis pathways of secondary metabolites such as flavonoids production. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis further revealed that the DEGs were involved in flavonoid biosynthesis and plant hormone signal transduction pathways, both of which are linked to cold stress response. To validate the accuracy of transcriptome sequencing data, quantitative real time PCR (qRT-PCR) analysis was performed on 10 selected DEGs. The expression patterns on these genes determined by qRT-PCR were consistent with the transcriptome sequencing results. Overall, this study provides valuable insights into the physiological and molecular mechanisms of cold tolerance in maize and provides a basis for the application of cold-tolerant maize germplasm resources and cold-responsive genes in maize breeding programs.