Integrated metabolome analysis and transcript profiles revealed a potential role of SWEETs in sugar accumulation during Carrot taproot development

Abstract

Background: Carrot is a root vegetable abundant in numerous nutritional values. Sugar is one of the most important carbohydrates in horticultural products that play important roles in plant growth and development and response to biotic and abiotic stresses. However, the dynamics of the metabolites including sugar during carrot root development still remain unclear. Here, the differential metabolites in carrot roots at different developmental stages were measured using an UPLC-ESI-MS/MS system. The accumulation profiles of metabolites, especially sugars, as well as the transcript patterns of Sugars Will Eventually be Exported Transporter (SWEET) genes were intensively examined.

Results: The results identified 727 metabolites over all the samples detected, of which, 539 metabolites were found to be differential accumulated. A total of 34 differentially accumulated sugar metabolites were identified over the period of root development. Furthermore, 17 DcSWEET genes were detected to be specifically expressed in the roots, indicating a potential for root enlargement and sugar accumulation in carrot root.

Conclusions: The results from the current study would help carrot breeding focused on yield and quality improvement.

Keywords: Daucus carota; Metabolites; Root development; SWEET; Sugar accumulation; Transcript profiles.

Fig. 1

Carrot taproots utilized for metabolomics analysis. Carrot roots were harvested at 25 (stage 1), 40 (stage 2) and 90 (stage 3) days after sowing. The scale bars represented 5 cm

Fig. 2

PCA plot of the root samples at three stages. Stage 1, 2, and 3 indicated carrot taproot samples collected at 25, 40, and 90 days after sowing, respectively

Fig. 3

Comparison of differential metabolites between samples. Blue and orange represented up- and down-regulated metabolites, respectively

Fig. 4

Venn diagram of metabolites among three comparison groups

Fig. 5

KEGG pathway analysis of differential metabolites identified during carrot development. Top 20 pathway enrichment categories were displayed

Fig. 6

Heatmap map visualization of the differential metabolites detected. Red indicates high abundance, whereas low relative metabolites are marked in green

Fig. 7

Clustered metabolite change profiles from developing carrot roots

Fig. 8

Differential accumulated sugar metabolites identified during carrot taproot development. Red and green represent high and low accumulation, respectively

Fig. 9

The phylogenetic tree of SWEET family members from rice, Arabidopsis, and carrot. At, Arabidopsis thaliana; Os, Oryza sativa; Dc, Dacus carota. AtSWEET, OsSWEET, and DcSWEET proteins are represented by blue triangles, red squares, and green dot, respectively

Fig. 10

The distribution of conserved motifs of DcSWEET family members. The colored bars correspond to ten different conserved sequences

Fig. 11

The heatmap of expression levels for DcSWEET genes during carrot development. Red and green represent high and low expression, respectively

Fig. 12

Expression profiles of DcSWEET genes during carrot root development. The data were expressed as mean ± standard deviation