CsMYB5a and CsMYB5e from Camellia sinensis differentially regulate anthocyanin and proanthocyanidin biosynthesis

Area of Science:

• Plant Molecular Biology
• Biochemistry
• Genetics

Background:

• Tea (Camellia sinensis) is a globally popular beverage rich in polyphenols.
• While many genes for polyphenol biosynthesis are known, the transcriptional regulation of pathways like proanthocyanidin (PA) synthesis remains poorly understood.
• R2R3-MYB transcription factors (TFs) are crucial regulators in plant secondary metabolism.

Purpose of the Study:

• To investigate the role of R2R3-MYB TFs in regulating PA and anthocyanin biosynthesis in tea plants.
• To identify specific MYB TFs involved in the late steps of the PA pathway.
• To elucidate the regulatory mechanisms controlling PA accumulation in tea.

Main Methods:

• Screening of tea transcriptome databases to identify R2R3-MYB TFs.
• Functional analysis of candidate TFs (CsMYB5a and CsMYB5e) through overexpression in *Nicotiana benthamiana* (tobacco).
• Analysis of anthocyanin and PA content in transgenic plants.
• Gene expression analysis using RNA-sequencing (RNA-seq) and quantitative real-time PCR (qRT-PCR).

Main Results:

• Overexpression of CsMYB5a led to decreased anthocyanin and increased polymeric PA in tobacco flowers.
• Overexpression of CsMYB5e increased dimethylaminocinnamaldehyde-stained PA content without affecting anthocyanin levels.
• Both CsMYB5a and CsMYB5e significantly upregulated genes involved in PA and anthocyanin biosynthesis pathways in transgenic flowers.
• Three UGTs and four GSTs were identified as potentially involved in PA and anthocyanin glycosylation and transport.

Conclusions:

• CsMYB5a and CsMYB5e are key regulators of proanthocyanidin biosynthesis in *Camellia sinensis*.
• These MYB TFs play distinct roles in modulating PA and anthocyanin accumulation.
• The study provides novel insights into the transcriptional control of secondary metabolite pathways in tea plants.