Comparative transcriptomics and metabolomics analyses provide insights into thermal resistance in lettuce (Lactuca sativa L.)

High temperature poses a major threat to sustainable development of the lettuce industry. Investigation of the mechanisms that regulate heat stress responses has great significance. Four lettuce accessions-two thermoto-lerant and two thermosensitive cultivars-were selected for comparative analysis. Subsequently, the metabolic changes in lettuce in response to heat treatment were investigated using untargeted metabolomic analysis. Several discriminatory metabolites were identified, including three amino acids, one carbohydrate, eight phenolic compounds, one terpene, one alcohol and one lignin. Transcriptomics analysis was performed in parallel using the same four lettuce accessions. The integrated analysis suggested that a large number of metabolites and genes detected with measurable changes during the heat response are involved in flavonoid biosynthesis. Additionally, 25 of the 31 transcription factors identified, including MYBs, WRKYs, NACs, bHLHs, MADSs, AP2/ERFs and bZIP, were also upregulated. Thus, this study provides a comprehensive understanding of the complex molecular mechanisms underlying the thermal stress responses of lettuce.