PlantView Supports Transcription Factor Function Research: FhMYB4: a dual-pathway repressor coordinating floral color and scent in Freesia hybrida

New progress has been made in the functional characterization of FhMYB4, a dual-pathway repressor coordinating flower color and fragrance in freesia.

Professor Xiang Gao's research team from Northeast Normal University published their findings in “New Phytologist” (IF = 8.1, top journal).

This study identifies the transcription factor FhMYB4 as a key repressor that coordinately regulates anthocyanin pigmentation and linalool biosynthesis in freesia. The findings reveal the molecular mechanism underlying the coordinated regulation of flower color and fragrance and provide a promising strategy for the precise breeding and trait improvement of ornamental plants.

To improve pollination efficiency and reproductive success, flowering plants have evolved a series of convergent floral traits known as pollination syndromes, among which flower color and floral fragrance are two of the most important characteristics. The researchers found that the transcription factor FhMYB4 acts as a key repressor coordinating the regulation of flower color (anthocyanin biosynthesis) and floral fragrance (linalool biosynthesis) in freesia. FhMYB4 suppresses both metabolic pathways through two distinct mechanisms. It directly binds to the promoters of anthocyanin biosynthetic genes, such as FhDFR3, and linalool biosynthetic genes, such as FhTPS1, thereby repressing their transcription. In addition, in the anthocyanin pathway, FhMYB4 interacts with bHLH proteins to disrupt the formation of the MBW activation complex, thereby indirectly suppressing anthocyanin biosynthesis.

FhMYB4 itself is transcriptionally activated by the flower color activator FhPAP1 and the floral fragrance activator FhMYB21L2, forming a negative feedback regulatory loop. While these activators promote metabolite biosynthesis, they simultaneously induce the expression of the repressor FhMYB4, thereby preventing excessive resource consumption and maintaining metabolic homeostasis.

The study further demonstrated that engineering FhMYB4, such as mutating its EAR repression motif or fusing it with a transcriptional activation domain, converts it into a potent activator capable of simultaneously enhancing the expression of genes involved in flower color and fragrance biosynthesis. This approach provides a new molecular tool for the precise breeding and trait improvement of ornamental plants.

Experiments using Plantview

In this study, the authors used D-luciferin potassium salt, a multifunctional imaging system, and a tube luminometer from Guangzhou Biolight Biotechnology to investigate the interaction between FhMYB4 and FhTT8L.

The luciferase complementation assay (LCA) demonstrated that FhMYB4 competitively binds to FhTT8L, thereby inhibiting the formation of the FhPAP1–FhTT8L complex. However, compared with FhPAP1, FhMYB4 exhibits a weaker binding affinity for FhTT8L.

FhMYB4 represses the FhPAP1–FhTT8L complex through its interaction with FhTT8L. (c) The LCA confirmed the interaction between FhMYB4 and FhTT8L. (e) FhMYB4 inhibited the formation of the FhPAP1–FhTT8L complex. (f) Compared with samples expressing FhPAP1-nLUC and cLUC-FhTT8L, weaker luciferase activity was observed in Nicotiana benthamiana leaves and Arabidopsis protoplasts co-expressing FhMYB4-nLUC and cLUC-FhTT8L.

DOI: org/10.1111/nph.71266