Metabolomic and Transcriptomic Analyses Reveal the Effects of Grafting on Nutritional Properties in Eggplant

Abstract

Grafting has a significant impact on the botany properties, commercial character, disease resistance, and productivity of eggplants. However, the mechanism of phenotypic modulation on grafted eggplants is rarely reported. In this study, a widely cultivated eggplant (Solanum. melongena cv. 'Zheqie No.10') was selected as the scion and grafted, respectively, onto four rootstocks of TOR (S. torvum), Sa (S. aculeatissimum), SS (S. sisymbriifolium), and Sm64R (S. melongena cv. 'Qiezhen No. 64R') for phenotypic screening. Physiological and biochemical analysis showed the rootstock Sm64R could improve the fruit quality with the increasing of fruit size, yield, and the contents of total soluble solid, phenolic acid, total amino acid, total sugar, and vitamin C. To further investigate the improvement of fruit quality on Sm64R, a transcriptome and a metabolome between the Sm64R-grafted eggplant and self-grafted eggplant were performed. Significant differences in metabolites, such as phenolic acids, lipids, nucleotides and derivatives, alkaloids, terpenoids, and amino acids, were observed. Differential metabolites and differentially expressed genes were found to be abundant in three core pathways of nutritional qualities, including biosynthesis of phenylpropanoids, phospholipids, and nucleotide metabolism. Thus, this study may provide a novel insight into the effects of grafting on the fruit quality in eggplant.

Keywords: fruit quality; grafted eggplant; metabolome; rootstocks; transcriptome.

Figure 1

Metabolomic analyses between Sm64R-grafted eggplant and self-grafted eggplant SG. (a) Principal component analysis of the metabolites in Sm64R-grafted eggplant and self-grafted eggplant SG. (b) Volcano plot analysis of different abundances of metabolites. Red color indicates high abundance, gray color indicates middle value, and green color indicates low abundance. (c) The number of different abundances of metabolites in each class. (d) Statistics of the different abundances of metabolites in each class. Orange color represents the number of higher accumulated metabolites; blue color represents the number of lower accumulated metabolites.

Figure 2

Transcriptomic analyses between Sm64R-grafted eggplant and self-grafted eggplant SG. SG. (a) Volcano plot analysis of DEGs. Red color shows high expression level, blue color shows middle value, and green color shows low expression value. (b) Principal component analysis of eggplant fruit samples. (c) Number of differentially expressed genes (DEGs) between Sm64R-grafted eggplant and self-grafted eggplant. (d) Circos plot analysis of the distribution of the DEGs along the physical map of the eggplant genome.

Figure 3

Functional enrichment analysis of DEGs. (a) GO classification of all DEGs in Sm64R-grafted eggplant and self-grafted eggplant SG. (b) GO enrichment analysis of DEGs. The size of the point indicates the number of enriched DEGs. (c) KEGG classification in the main class and subclass of all DEGs. (d) KEGG pathway enrichment analysis of DEGs.

Figure 4

Integrated transcriptomic and metabolomic analyses. (a) Heatmap demonstrating the clustering of DEMs and DEGs based on their correlation coefficients. (b) The 9-quadrant plot of DEMs and DEGs demonstrates the fold changes in metabolites and genes with Pearson correlation coefficients >0.8 in each group; the plot is divided from left to right and top to bottom into quadrants 1–9 with black dashed lines. (c) Classification plot of the top 20 DEMs with the highest change. (d) Correlation analysis was performed using Cytoscape and String, with p values > 0.001.

Figure 5

Map of differences in the metabolic pathways between Sm64R-grafted eggplant and self-grafted eggplant SG in phenylpropanoid biosynthesis, lipid metabolism, and nucleotide metabolism. Upregulated and downregulated metabolites/genes are highlighted in red and green, respectively.