Metabolome and transcriptome analyses for explore heat stress responses and adaptation mechanisms in Rhododendron henanense subsp. lingbaoense

In this study, we aimed to investigate the heat tolerance mechanism in Rhododendron henanense subsp. lingbaoense (Rhl). Rhl seedlings were treated at 40℃ (RLH), 32℃ (RLM), and 24℃ (RLC), and the changes in transcriptome and metabolome were compared. Overall, 78 differentially expressed metabolites were detected, and 8450 differentially expressed genes (DEGs) were identified. KEGG analysis revealed that the DEGs in RLH vs. RLC were mainly enriched in photosynthesis, secondary metabolic biosynthesis, and flavonoid biosynthesis. Most genes encoding glutathione-S-transferase were upregulated, whereas genes related to heat shock proteins were significantly downregulated. 31 genes related to photosynthesis were significantly upregulated (P-value < 0.001). It was speculated that these DEGs are related to the response of Rhl to high temperature stress (HTS). Overall, 9 TF families might be the key regulators of Heat stress response pathways in Rhl. Mining of DEGs revealed that the expression of some genes related to heat stress function increased highly significantly, e.g., the Rhe008987 related to Glutathione-S-transferase, Rhe016769 encoding peroxidase, and Rhe001827 encoding chalcone and stilbene synthases. Metabolome and transcriptome correlation analysis revealed that three comparison groups (RLH vs. RLC, RLH vs. RLM, and RLM vs. RLC) shared 12 metabolic pathways in which the DEMs were enriched. HTS inhibited or induced expression of genes in flavonoid biosynthesis pathway and led to decreace in kaempferol content and quercetin accumulation. HT induced expression of genes in ABC pathway, which may be one of the reasons for the significant accumulation of L-isoleucine, L-leucine, and L-proline. In this study, DEGs mining found that the expression of some genes related to heat stress function increased highly significantly. And two omics correlation analysis revealed that 12 metabolic pathways were enriched in three comparison groups. These results helped in elucidating the molecular mechanisms of response of Rhl to HTS.