Expression Analysis of the Anthocyanin Genes in Pink Spathes of Anthurium with Different Color Intensities

Anthurium ( Anthurium andraeanum ) is a tropical ornamental valued for its colorful spathe (modified bract) that subtends the inflorescence. The present genetic model for spathe color inheritance in anthurium does not account for differences among the red- and pink-spathed cultivars or for differences in the shades of pink among pink cultivars. To identify the mechanisms responsible for the variation in color and intensity, five genetically defined pink-spathed cultivars, with respect to the O , R , and M loci, with varying shade intensities, along with a genetically defined red-spathed cultivar (control), were analyzed at the mRNA, protein, chemical, and phenotypic levels at different spathe development stages. Spathe color values were recorded based on CIE L*a*b* system. Intensity of color ( L* , which represents lightness) correlated with the anthocyanin content, with L* showing a strong negative relationship with anthocyanin abundance. Additionally, the red spathe accumulated anthocyanin throughout the spathe developmental stages, whereas the pinks either produced anthocyanin at early stages of development, which decreased as the spathe matured or showed a marked delay in anthocyanin accumulation. The level of anthocyanin closely mirrored flavonoid 3′-hydroxylase ( F3 ′ H ) expression but did not correspond with the expression of any of the other genes assayed, chalcone synthase ( CHS ), flavanone 3-hydroxylase ( F3H ), dihydroflavonol 4-reductase ( DFR ), and anthocyanidin synthase ( ANS ). It was found that earlier the expression and higher the rate of expression of F3 ′ H during spathe development, the greater the accumulation of anthocyanin in the spathe. Differences in the a* color space parameter among cultivars also suggests that qualitative differences in color could be mediated through F3 ′ H . Other ancillary mechanisms that down regulate F3H , ANS , and DFR expression levels, evident in some pink cultivars, are discussed.