Abstract
Floral anthocyanin has multiple ecological and economic values, its biosynthesis largely depends on the conserved MYB-bHLH-WD40 (MBW) activation complex and MYB repressors hierarchically with the MBW complex. In contrast to eudicots, the MBW regulatory network model has not been addressed in monocots because of the lack of a suitable system, as grass plants exhibit monotonous floral pigmentation patterns. Presently, the MBW regulatory network was investigated in a non-grass monocot plant, Freesia hybrida. FhMYB27 and FhMYBx with different functional manners were confirmed to be anthocyanin related R2R3 and R3 MYB repressors, respectively. Particularly, FhMYBx could obstruct the formation of positive MBW complex by titrating bHLH proteins, whereas FhMYB27 mainly defected the activator complex into suppressor via its repression domains in C-terminus. Furthermore, the hierarchical and feedback regulatory loop was verified, indicating the synergistic and sophisticated regulatory network underlying Freesia anthocyanin biosynthesis was quite similar to that reported in eudicot plants.
Highlights
Floral anthocyanin has multiple ecological and economic values, its biosynthesis largely depends on the conserved MYB-bHLH-WD40 (MBW) activation complex and MYB repressors hierarchically with the MBW complex
Repressors FhMYB27 and FhMYBx from monocot F. hybrida, and demonstrated that they could down-regulate anthocyanin metabolism based on both transgenic Freesia petals or protoplasts and transient expression or promoter activation assays, revealing the hierarchical and feedback anthocyanin regulation might be relatively conservative in angiosperm plants
Bioinformatic and phylogenetic analysis inferred that FhMYB27 and FhMYBx were orthologs of petunia MYB27 and MYBx, respectively (Fig. 1)
Summary
Floral anthocyanin has multiple ecological and economic values, its biosynthesis largely depends on the conserved MYB-bHLH-WD40 (MBW) activation complex and MYB repressors hierarchically with the MBW complex. Since the elegant work with petunia MYB27 and MYBx illuminated the network of anthocyanin related transcription activators and repressors, increasing MYB repressors have been characterized in model and crop dicotyledons to negatively regulate anthocyanin biosynthesis in relatively conserved ways[10,15,23,25,26,27,28,29,30,31,32]. The MBW regulatory network responsible for floral anthocyanin biosynthesis in monocots has not been addressed to our knowledge, which needs attentions, because floral pigmentation is crucial for signaling to insect and animal pollinators and is an important trait to determine the ornamental values of horticultural plants[34]
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