Topology of TROL protein in thylakoid membranes of Arabidopsis thaliana

A Ubiquitin-Based Module Directing Protein-Protein Interactions in Chloroplasts

A promising approach for the genetic engineering of multiprotein complexes in living cells involves designing and reconstructing the interaction between two proteins that lack native affinity. Thylakoid-embedded multiprotein complexes execute the light reaction of plant photosynthesis, but their engineering remains challenging, likely due to difficulties in accurately targeting heterologous membrane-bound proteins to various sub-compartments of thylakoids. In this study, we developed a ubiquitin-based module (Nub-Cub) capable of directing interactions in vivo between two chloroplast proteins lacking native affinities. We applied this module to genetically modify thylakoid multiprotein complexes. We demonstrated the functionality of the Nub-Cub module in the model organism Arabidopsis thaliana. Employing this system, we successfully modified the Photosystem II (PSII) complex by ectopically attaching an extrinsic subunit of PSII, PsbTn1, to CP26-a component of the antenna system of PSII. Surprisingly, this mandatory interaction between CP26 and PsbTn1 in plants impairs the efficiency of electron transport in PSII and unexpectedly results in noticeable defects in leaf development. Our study not only offers a general strategy to modify multiprotein complexes embedded in thylakoid membranes but it also sheds light on the possible interplay between two proteins without native interaction.

Thylakoid Rhodanese-like Protein-Ferredoxin:NADP+ Oxidoreductase Interaction Is Integrated into Plant Redox Homeostasis System

In vascular plants, the final photosynthetic electron transfer from ferredoxin (Fd) to NADP+ is catalyzed by the flavoenzyme ferredoxin:NADP+ oxidoreductase (FNR). FNR is recruited to thylakoid membranes via an integral membrane protein TROL (thylakoid rhodanese-like protein) and the membrane associated protein Tic62. We have previously demonstrated that the absence of TROL triggers a very efficient superoxide (O2•-) removal mechanism. The dynamic TROL-FNR interaction has been shown to be an apparently overlooked mechanism that maintains linear electron flow before alternative pathway(s) is(are) activated. In this work, we aimed to further test our hypothesis that the FNR-TROL pair could be the source element that triggers various downstream networks of chloroplast ROS scavenging. Tandem affinity purification followed by the MS analysis confirmed the TROL-FNR interaction and revealed possible interaction of TROL with the thylakoid form of the enzyme ascorbate peroxidase (tAPX), which catalyzes the H2O2-dependent oxidation of ascorbate and is, therefore, the crucial component of the redox homeostasis system in plants. Further, EPR analyses using superoxide spin trap DMPO showed that, in comparison with the wild type, plants overexpressing TROL (TROL OX) propagate more O2•- when exposed to high light stress. This indicates an increased sensitivity to oxidative stress in conditions when there is an excess of membrane-bound FNR and less free FNR is found in the stroma. Finally, immunohistochemical analyses of glutathione in different Arabidopsis leaf cell compartments showed highly elevated glutathione levels in TROL OX, indicating an increased demand for this ROS scavenger in these plants, likely needed to prevent the damage of important cellular components caused by reactive oxygen species.

Photosynthetic modification of plants through recent technologies: a valuable way to ensure crop fortification

The 2030 Sustainable Development Goals of the United Nations include a strong emphasis on ending hunger worldwide. According to the 2019 Global Food Security Index, while 88% of countries claim there is sufficient food supply in their country, the sad reality is that 1 in 3 countries is facing insufficient availability of food supply, which means that in those countries, more than 10% of the population is malnourished. Since nutrition is crucial to leading a healthy life and satisfying food security needs, several governments have turned to national nutrition surveys to gauge the extent of malnutrition in their populations. Plants are able to grow, develop, and store nutrients by photosynthesis, which convert light into chemical energy through cell redox regulatory networks. A photosynthesis system's electron flow may be adjusted to accommodate varying light and environmental circumstances. Many techniques exist for controlling the flow of electrons emitted during light processes in order to save or waste energy. The two protein molecules TROL and flavoenzyme ferredoxin (oxidoreductase+NADP) (FNR) interact dynamically to form an excellent molecular switch capable of splitting electrons from the photosystem. The TROL-FNR bifurcation may be limited by either generating NADPH or preventing reactive oxygen species from propagating. TROL-based genome editing is an experimental method for enhancing plant stress and defensive responses, efficiency, and ultimately agricultural production.

Qualitative and quantitative dataset of TROL protein interaction with C3 and C4 ferredoxin: NADP+ oxidoreductases

Last step of electron transport from ferredoxin to NADP+ in photosynthesis light reactions catalyses ferredoxin: NADP⁺ oxidoreductase (FNR). FNR is present as soluble protein in stroma, but also bound to the protein complexes on the membrane with thylakoid rhodanase-like protein (TROL) and translocon on the inner envelope chloroplast membrane (Tic62), which have identical C terminal FNR binding domain [1,2]. During the electron transport, FNR anchored by TROL protein transfers electrons on NADP+ and forms NADPH which is then used in Calvin cycle as reducing agent. TROL is an integral membrane protein [3] with an inactive rhodanase-like domain (RHO) facing stroma which, as proposed earlier [4], could bind a small ligand leading to releasing or binding of FNR. FNR-TROL protein complex is necessary for optimal photosynthetic electron flow [1]. It has been shown that C4 plant maize FNR isomers have different N-terminal structure which determines binding affinity to protein complexes and different ratios of bound and unbound FNR in bundle sheath and mesophyll cells, depending on preferable photosynthetic electron transport [5]. Mutant Arabidopsis plant that contain maize FNR1 protein showed influence on dynamic association of FNR and change in excitation balance between photosystems which then influenced photo induced electron transport and finally photosynthesis [5]. In order to determine the influence of maize FNR1 on photosynthesis in C3 plants and difference in interaction strength with TROL, we preformed Yeast two hybrid screening, x-alpha-gal assay and β-galactosidase assay.