Integration of transcriptome and metabolome reveals key regulatory defense pathways associated with high temperature stress in cucumber (Cucumis sativus L.)

Abstract

High temperature stress seriously affects the quality and yield of vegetable crops, especially cucumber (Cucumis sativus L.). However, the metabolic dynamics and gene regulatory network of cucumber in response to high temperature stress remain poorly studied. In this study, we identified a heat-tolerant cucumber Gy14 and a heat-sensitive cucumber 32X. RNA-seq analysis of Gy14 and 32X under high temperature stress showed that some differentially expressed genes (DEGs) were related to the biosynthesis of secondary metabolites. Metabolomic analysis revealed that there were more phenylpropanoids and their downstream derivatives in Gy14 compared to that in 32X under Re_2d condition (2 normal days recovery after heat). Integrated analysis of transcriptome and metabolome revealed that these upregulated genes played a pivotal role in flavonoid biosynthesis. Moreover, high temperature stress significantly induced the expression of the gibberellin (GA) biosynthesis genes and exogenous application of GA₃ alleviated the damage of high temperature to cucumber seedlings. Together, these findings provided new insights into the transcriptome response and metabolomic reprogramming of cucumber against high temperature stress.

Keywords: Cucumber; Flavonoids; High temperature stress; Metabolome; Transcriptome.

Fig. 1

Phenotypic characterization of different cucumber accessions under high temperature stress. A The representative phenotype of different cucumber accessions exposed to high temperature stress in the field. NT, normal temperature. HT, High temperature. Bar, 5 cm. B The survival rate and (C) the chlorophylls content of different cucumber accessions under high temperature stress in the field

Fig. 2

Phenotypic characterization of Gy14 and 32X under high temperature stress conditions in glasshouse. A The representative morphology of Gy14 and 32X under high-temperature stress in glasshouse. Bar, 5 cm. B Schematic diagram of the leaf angle 1 and leaf angle 2. C Leaf angle 1 and (D) leaf angle 2 of Gy14 and 32X were measured after high-temperature stress. E The chlorophyll content and (F-G) the hypocotyl length of Gy14 and 32X at different high-temperature conditions. Data are presented as means ± SD (n = 10). Asterisks indicate the significant difference compared with control group (*, P < 0.05; **, P < 0.01; Student’s t-test)

Fig. 3

Transcriptome analysis of Gy14 and 32X cucumbers under high temperature stress. A PCA plot of transcriptome profiles from Gy14 and 32X under different temperature treatments. B The Number of DEGs in Gy14 and 32X under high temperature stress conditions. C-E The DEGs in Gy14 and 32X were shown by Venn diagrams. C Venn diagram of total DEGs between Gy14 and 32X under different high temperature stress conditions, (D) Co-upregulated DEGs between Gy14 and 32X at HS_1d condition, (E) Co-upregulated DEGs between Gy14 and 32X at Re_2d condition. F-G KEGG enrichment analysis of DEGs in Gy14 (F) and 32X (G) at Re_2d condition. Detailed data are shown in Supplemental Data S3

Fig. 4

Metabolome profile analysis of cucumber seedlings under high temperature stress. A Heatmap of all detected metabolites in Gy14 and 32X under Re_2d condition. B-C Differentially accumulated metabolites (DAMs) in Gy14 (B) and 32X (C) at Re_2d condition. D Clustering grouped the expression profiles of the metabolites in the Gy14 and 32X cucumber

Fig. 5

Metabolome analysis of Gy14 and 32X leaves under high temperature stress. A PCA plot of metabolome profiles of Gy14 and 32X under high temperature stress. B The number of DAMs in Gy14 and 32X. C Classification of DAMs in each comparison. D, F Classification of DAMs upregulated in Gy14 (D) and 32X (F) under high temperature stress. E, G KEGG pathway enrichment of DAMs in Gy14 (E) and 32X (G) under high temperature stress

Fig. 6

Summarized transcript and metabolite changes of phenylpropanoid pathway between Gy14 and 32X under high temperature stress. A Schematic representation of flavonoid biosynthesis pathway. B Heatmap of flavonoid biosynthetic genes filtered out from transcriptome data. Data are represented as log2 fold-change. C Summarized flavonoid biosynthetic metabolites changes. Data are represented as peak area

Fig. 7

Gibberellins (GAs) improve the high temperature tolerance of cucumber seedlings. A Expression pattern of gibberellin biosynthetic genes filtered out from transcriptome. Data are represented as log₂ fold-change. CPS, ent-copalyl diphosphate synthase; KS, ent-kaurene synthase; KO, ent-kaurene oxidase; KAO, ent-kaurenoic acid oxidase; GA20ox, GA3ox, GA oxidases. B The morphology of Gy14 and 32X seedlings treated by GA under high temperature stress. Bar, 5 cm. C-D The fresh weight (C) and plant height (D) of Gy14 and 32X under high temperature stress. E–H Changes of the leaf angle 1 and leaf angle 2 in Gy14 (E, F) and 32X (G, H). Asterisks indicate the significant difference compared with control group (*, P < 0.05; **, P < 0.01; Student’s t-test)