GLKs directly regulate carotenoid biosynthesis via interacting with GBFs in plants

Authors: SUN, TIANHU - Cornell University; ZENG, SHAOHUA - Cornell University; WANG, XIN - Boyce Thompson Institute; OWENS, LAUREN - Cornell University; FEI, ZHANGJUN - Boyce Thompson Institute; ZHAO, YUNDE - University Of California, San Diego; MAZOUREK, MICHAEL - Cornell University; Giovannoni, James; Li, Li

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2025
Publication Date: 2/14/2025
Citation: Sun, T., Zeng, S., Wang, X., Owens, L., Fei, Z., Zhao, Y., Mazourek, M., Giovannoni, J.J., Li, L. 2025. GLKs directly regulate carotenoid biosynthesis via interacting with GBFs in plants. New Phytologist. 246:645-665. https://doi.org/10.1111/nph.20457.
DOI: https://doi.org/10.1111/nph.20457

Interpretive Summary: GLK transcription factors are essential and conserved regulators of chloroplast development and chlorophyll biosynthesis and thus tightly linked to plant photosynthesis, performance, productivity, and crop quality. While GLKs are the subject of many investigations, the molecular mechanisms of GLKs in transcriptionally activating their targeted genes remain unclear. In addition, because chlorophyll and carotenoid biosynthesis are tightly regulated, whether GLKs directly regulate carotenoid pathway genes is unknown. Here, we demonstrate that GLKs directly regulate carotenoid biosynthesis in a GBF-dependent manner. GLKs and GBFs physically interact with each other to form the GLK-GBF regulatory module, which triggers phase separation-mediated nuclear condensates as the compartmented and concentrated transcriptional complexes and regulates their targeted gene expression. Our findings uncover a novel and conserved regulatory module for photosynthetic pigment biosynthesis.

Technical Abstract: Carotenoids are vital photosynthetic pigments for plants and provide essential nutrients for humans. However, our knowledge of the regulatory control of carotenoid biosynthesis remains limited. Golden2-like transcription factors (GLKs) are widely recognized as essential and conserved factors for chloroplast development and the major regulators of chlorophyll biosynthesis. Yet the molecular mechanisms by which GLKs transcriptionally activate their target genes are unclear. Here, we report that GLKs directly regulate carotenoid biosynthesis in a G-box Binding Factor (GBF)-dependent manner. Both in vitro and in vivo studies reveal that GLKs physically interact with GBFs. Through the direct binding of GBFs to the G-box motif, the GLK-GBF regulatory module transcriptionally activates Phytoene synthase (PSY), the gene encoding the rate-limiting enzyme for carotenoid biosynthesis. The ability of GLKs to promote carotenoid and chlorophyll biosynthesis is greatly diminished in the Arabidopsis gbf1/2/3 triple knockout mutants, showing the requirement of GBFs for GLK function. GLKs and GBFs form liquid-liquid phase separation-mediated nuclear condensates as the compartmented and concentrated transcriptional complexes. Our findings uncover a novel and conserved regulatory module for photosynthetic pigment biosynthesis through formation of GLK-GBF transcriptional complexes and nuclear biomolecular condensates in plants.