Functionality of the MYB1 Transcription Factor in the Transactivation of Leucoanthocyanidin Reductase (LAR) Promoters of Fragaria × Ananassa and Fragaria Chiloensis

MYB transcription factors (TFs) are involved in the regulation of flavonoid biosynthesis in both Chilean white strawberry (Fragaria chiloensis) and commercial strawberry (Fragaria × ananassa). There is evidence that MYB1 TF repress anthocyanin biosynthesis, but would also be participating in the regulation of the proanthocyanidin (PA) polymer synthesis, either in the activation or repression of the expression of PA-related genes. We investigated the role of the MYB1 TF in the regulation of the PA-associated structural gene leucoanthocyanidin reductase (LAR). The promoter regions of LAR were isolated from F. chiloensis and F. × ananassa genomes and named as pFcLAR and pFaLAR, respectively. Promoter analysis revealed several putative binding sites for MYBs and bHLH TFs. Then, dual luciferase assays were conducted to investigate whether MYB1 can act as a transactivator of LAR promoters in both species. In the long version of LAR promoters of both species (1381 bp upstream of ATG), the addition of MYB1 to the MYB10-bHLH3 complex repressed the activation. However, when using the medium version of the pFcLAR (815 bp upstream of ATG), MYB1 alone significantly activated the promoter, and no repression was observed when MYB1 was added to the MYB10-bHLH3 complex in the short pFa/FcLAR promoters (316 bp upstream of ATG). We propose that the FcMYB1 TF could regulate PA biosynthesis, and that its role, as either a repressor or activator, is dependent of other partners and the DNA sequence context of the promoter regions.