The calla lily (Zantedeschia hybrida) is a valued ornamental plant due to its unique shape and color variations. To determine the mechanisms responsible for color development in the calla lily spathe, we conducted a comparative transcriptomic analysis of the spathes of the black [Black Girl (B)], pink [Romantic (P)], and white [Ventura (W)] cultivars. The gene expression patterns in six spathe colors, including the preceding three colors as well as the amaranth [Promise (N)], red [Figo (F)], and yellow [Sun Club (Y)] cultivars were analyzed by real-time quantitative polymerase chain reaction (PCR). Transcriptomic analysis identified 25,165 differentially expressed genes. The transcription abundance and expression level of genes annotated as anthocyanidin reductase (ANR1, ANR2), basic-helix-loop-helix (bHLH1), and glutathione S-transferases (GST1) were significantly upregulated in B, and the expression of anthocyanidin synthase (ANS) was highest in B except for N. However, chalcone isomerase (CHI2) and dihydroflavonol 4-reductase (DFR1, DFR2) were expressed at significantly lower levels in P, W, and Y. Correlation analysis revealed that bHLH1 might act as a positive regulator of ANS expression, promoting anthocyanin synthesis. Moreover, GST1-encoded proteins may be related to the accumulation and transport of both anthocyanin and procyanidin in the calla lily spathe. It is speculated that the formation of the black spathe is related to the accumulation of anthocyanins and procyanidins. However, the low expression of CHI2, DFR1, and DFR2 may result in the inhibition of anthocyanin synthesis, which may lead to lightening of the spathe color. This preliminary study revealed the mechanism responsible for calla lily spathe color, identifying the key genes involved, thus providing effective gene resources and a theoretical basis for flower color molecular breeding.
The plant Zantedeschia hybrida is colorful and suitable for cut flowers and potted plants. This study employed a colorimetric method for the determination of spathe color phenotypes in 27 Z. hybrida cultivars and classified them into six major color classes. To characterize the coloration mechanism of the Z. hybrida spathe, this study explored the main colorants and pigment distribution using high-performance liquid chromatography (HPLC) with photodiode array detection (DAD) and electrospray ionization mass spectrometry (ESI-MS), ultra-performance liquid chromatography/hybrid triple quadrupole linear ion trap mass spectrometry (UPLC-Q-TRAP-MS), and tissue sections. The results showed that flavonoids were colorants in the spathes of different color groups and that cyanidin (Cy) was the main colorant, whereas carotenoids were not detected in the spathe. Total anthocyanin (TA) content was negatively correlated with lightness (L*) of coloration, such that a spathe with a higher TA and thicker pigmented cell layer showed a deeper color; however, there was no correlation between deep coloration in a spathe and flattened upper epidermal cells. The difference in TA was the main reason for the color variation among Z. hybrida of different color groups, whereas the total flavones and flavonols (TF) played a key role in the coloration of the orange and yellow group.