Light-sensitive Phytochrome-Interacting Factors (PIFs) are not required to regulate phytoene synthase gene expression in the root.

Carotenoids are plastidial isoprenoids essential for the protection of photosynthetic tissues against excess light. They also serve as precursors of apocarotenoid hormones such as abscisic acid (ABA) and strigolactones. The first enzyme of the carotenoid pathway, phytoene synthase (PSY), is also the main rate-limiting step. Unlike that observed in most plants, PSY is encoded by a single gene in Arabidopsis thaliana. Whereas the PSY gene is induced by light in photosynthetic tissues, a root-specific upregulation of PSY expression by salt stress and ABA has been recently demonstrated. Here we report that transcription factors of the Phytochrome-Interacting Factor (PIF) family, previously shown to repress PSY expression in etiolated seedlings and mature leaves, do not influence PSY expression in roots. Together, our results suggest that organ-specific pathways regulate PSY expression and hence carotenoid production in response to different environmental cues.