Activation Tagging Identifies a Conserved MYB Regulator of Phenylpropanoid Biosynthesis

TLDR

Plants synthesize diverse natural products that are often present at low levels and limited to specific tissues, impeding their evaluation. The study aims to develop a method to increase natural product accumulation using activation tagging. This is achieved by Agrobacterium‑mediated transformation with a T‑DNA containing cauliflower mosaic virus 35S enhancer sequences at its right border. Among ~5,000 activation‑tagged Arabidopsis lines, a plant with intense purple pigmentation was identified, revealing that enhancer insertion near an MYB transcription factor massively activates phenylpropanoid genes, elevating lignin, hydroxycinnamic acids, flavonoids, and anthocyanins, thereby demonstrating that activation tagging can overcome genetic controls and provide enriched tissue for phytochemical screening and gene discovery.

Abstract

Plants produce a wide array of natural products, many of which are likely to be useful bioactive structures. Unfortunately, these complex natural products usually occur at very low abundance and with restricted tissue distribution, thereby hindering their evaluation. Here, we report a novel approach for enhancing the accumulation of natural products based on activation tagging by Agrobacterium-mediated transformation with a T-DNA that carries cauliflower mosaic virus 35S enhancer sequences at its right border. Among ∼5000 Arabidopsis activation-tagged lines, we found a plant that exhibited intense purple pigmentation in many vegetative organs throughout development. This upregulation of pigmentation reflected a dominant mutation that resulted in massive activation of phenylpropanoid biosynthetic genes and enhanced accumulation of lignin, hydroxycinnamic acid esters, and flavonoids, including various anthocyanins that were responsible for the purple color. These phenotypes, caused by insertion of the viral enhancer sequences adjacent to an MYB transcription factor gene, indicate that activation tagging can overcome the stringent genetic controls regulating the accumulation of specific natural products during plant development. Our findings suggest a functional genomics approach to the biotechnological evaluation of phytochemical biodiversity through the generation of massively enriched tissue sources for drug screening and for isolating underlying regulatory and biosynthetic genes.