Transcriptional profiling of anthocyanin biosynthesis in variegated and non-variegated dorsal petal regions of Impatiens uliginosa.

backgroundPetal variegation is an important ornamental trait in flowering plants and has major implications for both evolutionary biology, because it can promote speciation and diversity, and horticulture, because it enhances aesthetic appeal and commercial value. Here, we used Impatiens uliginosa as a model system and combined morphological, anatomical, physiological, biochemical, transcriptomic, and molecular approaches to investigate the mechanisms underlying petal variegation.

resultsFreehand sectioning revealed that pigments were predominantly localized in the upper epidermal cells. Compared with the non-variegated dorsal petal regions, the variegated dorsal petal regions contained approximately three times as many pigment-accumulating cells; these cells were smaller, more densely arranged, and exhibited higher pigment density per unit area, collectively contributing to the darker coloration of the variegated regions. Pigment-content analysis showed that the variegated dorsal petal regions accumulated significantly higher levels of total carotenoids, anthocyanins, and flavonoids than the non-variegated dorsal petal regions. Semi-quantitative analysis further indicated that anthocyanin-related compounds, particularly delphinidin, pelargonidin, and peonidin derivatives, were enriched in the variegated dorsal petal regions. To investigate the molecular basis of this differential pigmentation, we performed comparative RNA-seq analysis of the variegated and non-variegated dorsal petal regions and identified a suite of candidate genes potentially involved in variegation formation. Functional validation of one candidate, IuMYB114, was carried out using virus-induced gene silencing (VIGS). Silencing of IuMYB114 resulted in a significant reduction in both the size and color intensity of the variegated dorsal petal regions. qRT-PCR analysis confirmed that IuMYB114 expression in silenced plants was only 11% of that in wild-type plants. Moreover, the expression of several key anthocyanin-biosynthetic genes, including IuANS, IuUFGT, and IuF3'5'H, was significantly downregulated in the silenced lines.

conclusionsTaken together, these results suggest that IuMYB114 is likely associated with the positive regulation of anthocyanin biosynthesis and may play an important role in the formation of variegated and non-variegated dorsal petal regions in I. uliginosa, potentially through the regulation of anthocyanin biosynthetic genes. The spatially restricted expression of IuMYB114 may therefore contribute to differential anthocyanin deposition and, consequently, to petal variegation.