Integrative Transcriptomics and Proteomics Analyses Provide Molecular Insights into High-Temperature Tolerance of Pitaya (Hylocereus polyrhizus)

High temperature (HT) is one of the most adverse environmental stresses altering the quality value of fruits. However, knowledge of the molecular responses of pitaya to HT stress remains elusive. Hence, the present study aimed to reveal key HT tolerance mechanisms of pitaya through an integrated transcriptome and proteome analysis of two contrasting varieties, C-130 (heat tolerant) and H17-10 (heat sensitive). We identified a total of 5783 DEGs (differentially expressed genes) and 2101 DEPs, of which 376 DEGs and DEPs were significantly correlated. Enrichment analyses unveiled biosynthesis of secondary metabolites, plant hormone signal transduction, MAPK-signaling pathway-plant, protein processing in endoplasmic reticulum, pyruvate metabolism, and cysteine and methionine metabolism as the key molecular responsive mechanisms. Particularly, heat shock transcription factors (HSFs), glutathione metabolism and brassinosteroids (BR) are essential for heat tolerance in pitaya. Major induced genes in these pathways were filtered out and examined. Furthermore, we uncovered 18 potential candidate genes for improving pitaya heat tolerance capability. Particular attention should be paid to the genes HU05G01771 and HU10G01257 encoding cytochrome P450 85A-like (related to BR synthesis) and HSF B-2a, respectively. Our findings disclose key molecular players responding to HT in pitaya, providing genetic resources for enhancing the crop heat tolerance.