AaMYB3 interacts with AabHLH1 to regulate proanthocyanidin accumulation in (Hort.)-another strategy to modulate pigmentation.

Proanthocyanidins (PAs), also known as "condensed tannins", are colorless metabolites produced through the flavonoid pathway that are involved in stress resistance in plants. Because PAs are involved in the anthocyanin biosynthetic pathway, they play a role in the modification of pigmentation conferred by anthocyanins in ornamental organs. In this study, we isolated the gene and functionally characterized an R2R3-MYB transcription factor (TF), AaMYB3, and a basic helix-loop-helix TF, AabHLH1, from (Hort.), a typical tropical flower. is primarily expressed in the spathe and negatively correlates with anthocyanin accumulation. A complementation test in an mutant showed that AabHLH1 successfully restores the PA-deficient seed coat phenotype. The ectopic overexpression of alone or its coexpression with 1 in transgenic tobacco resulted in light pink or even pale-pink corolla limbs by reducing their anthocyanin levels and greatly enhancing their accumulation of PAs. This overexpression of the anthurium TF genes upregulated the late anthocyanin enzyme-encoding genes ( and ) and the key PA genes ( and ) in transgenic tobacco. The interaction between AaMYB3 and the AabHLH1 protein was confirmed using yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays. In the developing red spathes of the cultivars "Vitara" and "Tropical", the expression of was closely linked to PA accumulation, and was coexpressed with , , , , , and . The expression pattern of was similar to that of . Our results suggest that AaMYB3 and AabHLH1 are involved in the regulation of PA biosynthesis in anthurium and could potentially be used to metabolically engineer PA biosynthesis in plants.