Abstract
In plants, the phenylpropanoid pathway is responsible for the synthesis of a diverse array of secondary metabolites that include lignin monomers, flavonoids, and coumarins, many of which are essential for plant structure, biomass recalcitrance, stress defense, and nutritional quality. Our previous studies have demonstrated that Populus trichocarpa PtrEPSP鈥怲F, an isoform of 5鈥恊nolpyruvylshikimate 3鈥恜hosphate (EPSP) synthase, has transcriptional activity and regulates phenylpropanoid biosynthesis in Populus . In this study, we report the identification of single nucleotide polymorphism (SNP) of PtrEPSP鈥怲F that defines its functionality. Populus natural variants carrying this SNP were shown to have reduced lignin content. Here, we demonstrated that the SNP鈥恑nduced substitution of 142nd amino acid (PtrEPSP鈥怲FD142E) dramatically impairs the DNA鈥恇inding and transcriptional activity of PtrEPSP鈥怲F. When introduced to a monocot species rice (Oryza sativa ) in which an EPSP synthase isoform with the DNA鈥恇inding helix鈥恡urn鈥恏elix (HTH) motif is absent, the PtrEPSP鈥怲F, but not PtrEPSP鈥怲FD142E, activated genes in the phenylpropanoid pathway. More importantly, heterologous expression of PtrEPSP鈥怲F uncovered five new transcriptional regulators of phenylpropanoid biosynthesis in rice. Collectively, this study identifies the key amino acid required for PtrEPSP鈥怲F functionality and provides a strategy to uncover new transcriptional regulators in phenylpropanoid biosynthesis.
