AUREOCHROME 1b A regulator of pigment biosynthesis in Phaeodactylum tricornutum

Diatoms have recently emerged as promising platforms for producing high value terpenoids yet the regulatory mechanisms governing their terpenoid metabolism remain poorly understood. Recent work in the model diatom Phaeodactylum tricornutum identified the first transcription factors influencing the terpenoid biosynthesis pathway. Building on these findings, we mined the PhaeoNet transcriptional network and pinpointed two additional TF candidates AUREOCHROME 1b and sigma factor 70.4 whose expression is tightly coregulated with the methylerythritol 4phosphate pathway. We generated episomal overexpression lines for these two TFs, alongside the previously characterized carotenoid regulating TFs PtHSF1 and PtHSF3, and assessed their impact on pigment content, growth, and global gene expression by RNAseq. Transcriptome profiling revealed that each TF upregulates distinct sets of genes involved in pigment biosynthesis, pigment binding, and photosynthesis. Phenotypically, overexpression of AUREO1b, PtHSF1, and PtHSF3 led to increased pigment accumulation, whereas sigma factor70.4 overexpression did not alter pigment levels. These results expand our understanding of transcriptional control over terpenoid and pigment pathways in diatoms.