Differences in Anthocyanin Biosynthesis Drive Flower Coloration Variations in Pansy (Viola × Wittrockiana Gams)

Pansies (Viola × wittrockiana Gams.) are widely cultivated ornamental plants due to their diverse flower colorations. However, the mechanisms underlying flower coloration remain unclear. In this study, the flower color characteristics of six lines-white (WP), light yellow (LYP), yellow (YP), orange (OP), blue (BP), and black purple (BPP)-pansies were evaluated. Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS/MS) was used to investigate the anthocyanin components of pansies. A total of 41 anthocyanins were identified, with BPP showing the largest variation and the highest anthocyanin contents. Delphinidin was the major anthocyanin in all six lines and was the predominant anthocyanin utilized in the four equations for determining color coefficients (L*, b*, C, and h). The expression patterns of anthocyanin structural genes were determined using real-time quantitative reverse transcription PCR (qRT-PCR). The anthocyanin biosynthesis pathway was restricted, starting from CHS and F3H in WP and LYP. The inhibition of CHI impaired anthocyanin accumulation and led to elevated chalcone content, resulting in the yellow color of YP and OP. The different expression levels of F3'H, F3'5'H, and DFR caused different anthocyanin branches in BP and BPP. Therefore, this study provides insights into the mechanisms of color diversity in pansies, as well as gene resources for flower color modification in ornamentals.