Ectopic expression of the Anthurium andraeanum (Hort.) R2R3-MYB genes AaMYB4 and AaMYB5 enhance the flower color in transgenic tobacco

Abstract

Anthocyanin coloration is crucially important for ornamental traits in Anthurium andraeanum. However, the molecular mechanisms responsible for anthocyanin accumulation in this important ornamental plant are poorly understood. Here, we isolated and functionally characterized two R2R3-MYB transcription factor genes AaMYB4 and AaMYB5 from A. andraeanum. Analysis of amino acid sequences indicate that both AaMYB4 and AaMYB5 share homology with the C1 subgroup R2R3-MYBs from monocots. AaMYB4 and AaMYB5 proved to be nucleus-localized proteins. Spatial and temporal expression analysis of AaMYB4 and AaMYB5 suggested that AaMYB4 was mainly expressed in the spathe and young leaves, whereas AaMYB5 was mainly expressed in the young leaves and the spadix. Although the expression patterns of AaMYB4 and AaMYB5 did not correlate with anthocyanin accumulation in the spathe and spadix of cultivar Vitara and Topical, they were positively correlated with anthocyanin concentration in the developing leaves of ‘Tropical’ and were coordinately expressed with key anthocyanin biosynthesis pathway genes. The ectopic expression of AaMYB4 and AaMYB5 in tobacco triggered the accumulation of anthocyanins in the corolla limbs of T1 transgenic progeny, and induced the up-regulation of expression of the key enzyme genes in the anthocyanin biosynthesis pathway of tobacco. Overexpression of AaMYB5 in tobacco also markedly up-regulated the expression of the endogenous MYB regulator gene NtAn2 involved in anthocyanin biosynthesis. Our findings suggest that both AaMYB4 and AaMYB5 from A. andraeanum are involved in the regulation of anthocyanin biosynthesis and have potential value in the metabolic engineering of anthocyanin biosynthesis in plants. AaMYB4 and AaMYB5 are R2R3-MYB transcription factors from Anthurium andraeanum. Overexpression of the two genes in tobacco resulted in large anthocyanin accumulation in the corolla limbs.