A synthetic switch based on orange carotenoid protein to control blue light responses in chloroplasts

Abstract

Synthetic biology approaches to engineer light‐responsive system are widely used, but their applications in plants are still limited, due to the interference with endogenous photoreceptors. Cyanobacteria, such as Synechocystis spp., possess a soluble carotenoid associated protein named Orange Carotenoid binding Protein (OCP) that, when activated by blue‐green light, undergoes reversible conformational changes that enable photoprotection of the phycobilisomes. Exploiting this system, we developed a new chloroplast‐localized synthetic photoswitch based on a photoreceptor‐associated protein‐fragment complementation assay (PCA). Since Arabidopsis thaliana does not possess the prosthetic group needed for the assembly of the OCP2 protein, we implemented the carotenoid biosynthetic pathway with a bacterial β‐carotene ketolase enzyme (crtW), to generate keto‐carotenoids producing plants. The novel photoswitch was tested and characterized in Arabidopsis protoplasts with experiments aimed to uncover its regulation by light intensity, wavelength, and its conversion dynamics. We believe that this pioneer study establishes the basis for future implementation of plastid optogenetics to regulate organelle responses, such as gene transcription or enzymatic activity, upon exposure to specific light spectra.One-sentence summaryInspired by the light-driven conformational transitions of orange carotenoid proteins of cyanobacteria, we generated a molecular device able to switch its dimeric state in response to blue light.

Here comes the sun: How optimization of photosynthetic light reactions can boost crop yields

“…Upon absorption of strong blue–green light, the noncovalently bound ketocarotenoid transfers from the CTD to the NTD, thereby undergoing a conformational change and a shift in color from orange to red, thus activating the quenching state. OCP has not only been expressed in ketocarotenoid‐producing microalgae for better solubilization of the ketocarotenoids canthaxanthin and astaxanthin for their use as nutraceuticals (Pivato et al, 2021), but is also being exploited as a possible photoswitchable protein in plants with implementations for plastid optogenetics, artificial photosynthesis and synthetic biology due to its light‐dependent conformational changes and uniqueness in cyanobacteria (Andreoni et al, 2017; Lechno‐Yossef et al, 2017; Dominguez‐Martin and Kerfeld, 2019; Piccinini et al, 2021).…”

Review of the structures and functions of algal photoreceptors to optimize bioproduct production with novel bioreactor designs for strain improvement

“…PRs able to detect alterations in light intensity and wavelengths which then trigger specific signal transduction pathways that cascade down to regulate developmental processes, metabolism, photosynthesis, photo orientation, and control of the circadian clock (Kianianmomeni & Hallmann, 2014). Well known PRs include channelrhodopsins, phototropins, BLUF proteins, cryptochromes (Beel et al, 2012, 2013; Christie, 2007; Takahashi et al, 2007), there are also more recently discovered receptors such as DUC1, OCP, and HpChR1 (Makita et al, 2021; Piccinini et al, 2021; Tao et al, 2021). This variety of PRs can be targeted to optimize key metabolic processes of targeted products.…”