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Figure 1. 

Phenotypes of VwTYDC-silenced Viola × wittrockiana. (a) Blank control; (b) flower phenotype after infection with pTRV2-VwCHS; (c) flower phenotype after infection with pTRV2-VwANS; (d) flower phenotype after infection with pTRV2-VwTYDC.

Figure 2. 

Effect of tyrosine treatment on non-blotched areas of Viola × wittrockiana petals. (a) ddH₂O treatment; (b) tyrosine treatment. The treated areas are marked by a red box.

Figure 3. 

Violin plot of anthocyanins in petals of Viola × wittrockiana treated with tyrosine or ddH₂O. The box in the middle represents the interquartile range. The black horizontal line in the middle is the median, and the outer shape represents the distribution of the data.

Figure 4. 

Heatmap of the contents of the 24 compounds detected in different Viola × wittrockiana samples analyzed by hierarchical clustering analysis. The horizontal axis shows the sample information, and the vertical axis shows the metabolite information. The tree on the left of the figure shows the metabolite clustering, and the scale is the metabolite content after standardization. A deeper red color indicates a higher content, and gray indicates that the compound was not detected. Groups indicate the different treatments. CK: ddH₂O treatment; Tyr: tyrosine treatment.

Figure 5. 

The relative expression levels of anthocyanin biosynthesis and transcription factor genes in Viola × wittrockiana petals that received tyrosine (Tyr) or ddH₂O (CK) treatment. * p ≤ 0.05, ** p ≤ 0.01, *** p ≤ 0.001.

Figure 6. 

ABA contents in Viola × wittrockiana from different treatment groups. ** p ≤ 0.01. CK, ddH₂O treatment. Tyr, tyrosine treatment.

Figure 7. 

Expression levels of anthocyanin biosynthesis genes and transcription factors in Viola × wittrockiana with and without ABA treatment. * p ≤ 0.05, ** p ≤ 0.01, ***p ≤ 0.001.

Figure 8. 

Possible pathways by which tyrosine treatment may promote anthocyanin biosynthesis in Viola × wittrockiana. The red color represents upregulation of genes and metabolites. The dashed arrow represents the possible pathway. PAL/TAL indicates that PAL may function like TAL in pansy, although this remains to be verified. PAL: phenylalanine ammonia-lyase; TAL: tyrosine ammonia-lyase; C4H: cinnamate 4-hydroxylase; 4CL: 4-coumarate-CoA ligase; HCT: shikimate O-hydroxycinnamoyltransferase; C3′H: 5-O-(4-coumaroyl)-D-quinate 3'-monooxygenase; CHS: chalcone synthase; F3H: naringenin 3-dioxygenase; F3′H: flavonoid 3'-hydroxylase; F3′5′H: flavonoid 3',5'-hydroxylase; DFR: flavanone 4-reductase; ANS: anthocyanidin synthase; UGT: UDP glucuronosyltransferase, falconoid 3-O-glycosyltransferase; CCoAOMT: caffeoyl-CoA O-methyltransferase; VwNCED: 9-cis-epoxycarotenoid dioxygenase; VwABA2: xanthoxin dehydrogenase; VwAAO3: abscisic-aldehyde oxidase; VwCYP707A: (+)-abscisic acid 8'-hydroxylase.