SmMYB113 Is a Key Transcription Factor Responsible for Compositional Variation of Anthocyanin and Color Diversity Among Eggplant Peels

Abstract

To understand the color formation mechanism in eggplant (Solanum melongena L.) peel, a metabolomic analysis was performed in six cultivars with different peel colors. A total of 167 flavonoids, including 16 anthocyanins, were identified based on a UPLC-MS/MS approach. Further analysis revealed that the delphinidins/flavonoids ratio was consistent with the purple coloration of eggplant peels, and SmF3'5'H expression level was consistent with the delphinidin 3-O-glucoside and delphinidin 3-O-rutinoside contents, the main anthocyanins in the purple-peels eggplant cultivars identified in this study. SmMYB113 overexpression promoted anthocyanins accumulation in eggplant peels and pulps. Metabolomic analysis revealed that delphinidins were still the main anthocyanins class in the peels and pulps of SmMYB113-OE4, but most anthocyanins were glycosylated at the 5-position of the B-ring. Our results provide new insights into the anthocyanin composition of eggplant peels and demonstrate the importance of SmMYB113 in stimulating anthocyanin biosynthesis in eggplant fruits.

Keywords: MYB transcription factor; anthocyanin biosynthesis; eggplant; metabolome; peels color.

FIGURE 1

Overviews of the flavonoid-targeted metabolism data from the peels of six eggplant cultivars. (A) The identified number of total flavonoids and anthocyanins; (B) the relative contents of total flavonoids and anthocyanins; (C) the ratio of anthocyanins in the total flavonoids; (D) the ratio of cyanidins, delphinidins, and pelargonidins in the total flavonoids, respectively. Values are means ± SD (n = 3), same as following. Means denoted by the same letter did not differ significantly at P < 0.05 according to Duncan’s multiple range test.

FIGURE 2

Veen analysis and heat map analysis of the identified anthocyanins, and the expression analysis of SmF3′H and SmF3′5′H in the peels of six eggplant cultivars. (A) Four-way Venn diagram analysis of the identified anthocyanins in the purple-peels colored eggplant cultivars with the sum of identified anthocyanins in the other three eggplant cultivars without purple peels color; (B) heat map of anthocyanins biosynthesis pathway. This pathway is constructed based on the KEGG pathway and literary references. Each colored row represents the log10 (content) of a metabolite; (C) the transcript ratio of SmF3′H and SmF3′5′H, and the relative expression level of SmF3′5′H in the peels of six eggplant cultivars at fruiting, growth and maturity stages. * represents significance at P < 0.05 comparing with those in No. 108.

FIGURE 3

SmMYB113 controls anthocyanin biosynthesis in eggplants. (A) The process of eggplant transformation and phenotypes of SmMYB113-OE eggplant line; PCR verification (B) and expression analysis (C) of SmMYB113 in the four SmMYB113-OE eggplant lines. M represents 2,000 bp marker; P represents positive control using the pRII-SmMYB113 vector; WT represents negative control using the DNA of No. 108; (D) the anthocyanin content in the peels and pulps of WT and the four SmMYB113-OE eggplant lines. Asterisk represents significance at P < 0.05 comparing with WT.

FIGURE 4

Overviews of the flavonoid-targeted metabolism data from the peels and pulps of SmMYB113-OE4, and heat map of flavonoid biosynthesis pathway. (A) The number of flavonoids different accumulated in the peels and pulps of SmMYB113-OE4 compared with WT at a level of |log₂^{(fold change)}| ≥ 1 and VIP ≥ 1; (B) Venn diagrams of different accumulated flavonoids by overexpression SmMYB113 in the peels and pulps of eggplants; (C) the changed ratio of eight flavonoids classes by overexpression SmMYB113; (D) the ratio of cyanidins, delphinidins, and pelargonidins in the total flavonoids, respectively; (E) heat map of flavonoids biosynthesis pathway. This pathway is constructed based on the KEGG pathway and literary references. Each colored row represents the log10 (content) of a metabolite.

FIGURE 5

Comprehensive comparison of the two metabolomic data in eggplant. (A) The ratio of anthocyanins in the peels or pulps of three purple peels colored cultivars and SmMYB113-OE4 compared with those in No. 108; (B) the ratio of flavonoids (without anthocyanins) in the peels or pulps of three purple peels cultivars and SmMYB113-OE4 compared with those in No. 108; the ratio of cyanidins, delphinidins, and pelargonidins in the total anthocyanins in the peels three purple peels colored cultivars (C) and in the peels and pulps of SmMYB113-OE4 (D).