Exploring the shikimate-phenylpropanoid pathway in Phaeodactylum tricornutum under different cultivation conditions

The phenolic compounds are the most common antioxidants produced under adverse conditions by photosynthetic organisms to survive both abiotic and biotic stressors and find application in many industrial fields. The most abundant phenolic compounds are flavonoids such as apigenin and phenylpropanoids such as p-coumaric acid, caffeic acid and ferulic acid. Phenylproponoids are synthetized through the shikimate-phenylpropanoid pathway, which involves several enzymes that might be differently expressed depending on the environmental conditions or in response to stress. Despite being a diatom model species, in Phaeodactylum tricornutum the shikimate-phenylpropanoid pathway is still poorly characterized from a genetic and functional point of view. Only scares studies are also available for P. tricornutum quantitative and qualitative composition of phenylpropanoids. Here, we investigate the natural phenylpropanoid production of P. tricornutum CCAP 1055/1 by combining metabolic and bioprocess engineering. We overexpressed two native proteins of the shikimate pathway, i.e. the 3-deoxy-D-arabinoheptulosonate 7-phosphate (DAHP) synthase and the shikimate kinase (SK), known to be the main flux-controlling steps in higher plants. Additionally, we assessed different stress cultivation conditions which potentially affect the phenylpropanoids synthesis, i.e. light stress coupled with iron depletion. The present study will provide new insights into the regulation of this pathway in order to modulate the phenylpropanoid biosynthesis in diatoms in order to exploit their potential as a production platform.