Gene Expression and Secondary Metabolic Regulation Underlying Variegated Leaf Formation in Sweetpotato

Variegated sweetpotato leaves are of interest for ornamental and functional-food applications, yet the molecular and metabolic basis of their coloration remains poorly understood. A sweetpotato accession with variegated leaves was found incidentally in the field, with rare and vivid Pink-purple coloration in the apical leaves. To investigate the mechanism underlying this interesting phenotype, this material was maintained in the laboratory, and variegated and normal green leaves from this plant were analysed by transcriptome profiling, miRNA sequencing and metabolome analysis. By integrating differential mRNA expression analysis, target-gene prediction, miRNA sequencing and metabolite identification, we screened candidate miRNA-mRNA modules associated with this leaf-colour formation. Using FDR < 0.05 and |log2FC| ≥ 1 as thresholds, 49 differentially expressed miRNAs and 692 regulatory relationships involving differentially expressed target mRNAs associated with these miRNAs were identified. Functional annotation indicated that the iba_638_x1- G10133|TU16655 and iba_730_x1- G3592|TU5891 modules were associated with anthocyanin/flavonoid biosynthesis and vacuolar transport, respectively. Metabolome analysis showed that the total relative abundance of flavonoids in Pink leaves was 2.98-fold higher than that in CK, and 28 flavonoids accumulated to more than 2-fold higher levels in Pink than in CK. The differentially accumulated metabolites mainly included anthocyanin glycosides, such as petunidin-3-O-glucoside, delphinidin-3-O-glucoside and cyanidin-3,5-O-diglucoside, and flavonol glycosides, such as quercetin-3-O-sophoroside, isorhamnetin-3-O-glucoside and kaempferol-3-O-sophoroside-7-O-glucoside. These results indicate that the variegated phenotype of Pink leaves is mainly associated with differential accumulation of anthocyanin glycosides and flavonol glycosides.