Two basic-helix-loop-helix genes (MYC-146 and GL3) from Arabidopsis can activate anthocyanin biosynthesis in a white-flowered Matthiola incana mutant

Basic helix-loop-helix (bHLH) proteins, similar to mammalian Myc transcription factors, regulate the anthocyanin biosynthetic pathway in both monocots and dicots. Two Arabidopsis bHLH genes, GLABRA3 (GL3) and MYC-146, encode proteins that are similar throughout the predicted amino acid sequence to R and DELILA, which regulate anthocyanin production in maize and snapdragon, respectively. Northern blot analysis indicates that MYC-146 is most highly expressed in flower buds and flowers. Expression of a MYC-146 cDNA from the CaMV 35S promoter was unable to complement the anthocyanin deficiency in a ttg1 mutant of Arabidopsis and resulted in no obvious phenotypic change in Columbia plants. However, transient expression of GL3 and MYC-146 upon microprojectile bombardment of petals of a white-flowered mutant of Matthiola incana was able to complement anthocyanin deficiency. The lack of anthocyanin-deficient Arabidopsis mutants mapping to the locations of GL3 and MYC-146 suggests that the two bHLH proteins may be partially redundant and overlap in function.