Discovery of atypical phenylalanine ammonia-lyases enhances phenylpropanoid production
Researchers identify diverse feedback regulation of PAL enzymes in 14 plant species, enhancing phenylpropanoid biosynthesis.
Plants synthesize various phenylpropanoids, essential for medicine, nutrients, and biomaterials, while also acting as a significant global carbon sink. Phenylpropanoids are primarily derived from L-phenylalanine (Phe) through the action of Phe ammonia-lyase (PAL), an enzymatic activity that is tightly regulated and limits phenylpropanoid production. However, the regulation of PAL enzymes across different plant species is not well understood.
A phylogeny-guided biochemical screening revealed complex feedback regulation of PAL enzymes from 14 different plant species. This screening identified a previously uncharacterized PAL clade, termed PALnc (from noncanonical), with some members showing feedback activation by p-coumaric acid, caffeic acid, and 4-hydroxyphenylpyruvic acid in vitro. The transient expression of two PALnc genes, EgPALnc from Elaeis guineensis and PmPALnc2 from Piper methysticum, in Nicotiana benthamiana leaves resulted in elevated phenylpropanoid content, supported by the high stability of PALnc proteins in planta compared to canonical PALs.
In contrast, overexpression of Arabidopsis thaliana PAL1 (AtPAL1) in stable transgenic lines led to low accumulation of AtPAL1 protein and minor metabolic effects. The introduction of EgPALnc resulted in high levels of EgPALnc protein and hyperaccumulation of hydroxycinnamate derivatives. These findings reveal previously overlooked diversity in the regulation of phenylpropanoid biosynthesis and highlight atypical PALs within the PALnc clade as valuable tools for enhancing phenylpropanoid production in plants.
