R2R3-MYB gene family: Genome-wide identification provides insight to improve the content of proanthocyanidins in Trifolium repens.

The R2R3-MYB family is one of largest transcription factor families in plants playing significant roles in regulating anthocyanin and proanthocyanidin biosynthesis. Proanthocyanidins are one of major objectives to improve the quality of white clover (Trifolium repens L.), which have a beneficial effect on ruminant to prevent the lethal pasture bloat. A total of 133 TrR2R3-MYB genes were identified and distributed on all 16 chromosomes based on the whole genome information of white clover. Also, by exploring the gene structure, motifs and duplication events of TrR2R3-MYBs, as well as the evolutionary relationship with TrR2R3-MYB genes of other species, 10 TrR2R3-MYB genes with the potential to regulate the anthocyanins and proanthocyanidins biosynthesis were screened. These TrR2R3-MYB genes responded significantly to low temperature in white clover. In addition, they have different expression patterns in leaves, petioles and inflorescences of white clover. Importantly, TrMYB116 and TrMYB118 may positively regulate anthocyanin accumulation and low temperature response in white clover. TrMYB118 may also be associated with anthocyanin pigmentation pattern in Purple leaves. This study provides a basis for verifying the function of TrR2R3-MYB and breeding white clover cultivars with high proanthocyanidins.