A novel perspective for Photosystem I: an emerging hub for the functional integration of photosynthesis and metabolism

BLANCO, NICOLAS E; GOLLAN, PETER J; MENGIN, VIRGINIE; NIKKANEN, LAURI; FUSARI, CORINA M.

Frontiers in Plant Sciences

Frontiers

Lugar: Lausanne; Año: 2022

1664-462X

Energy conversion via photochemical reactions, and gas exchange that facilitates accessibility and conversion of CO2 to photoassimilates are mutually dependent and directly influenced by environmental conditions (Matuszynska et al., 2019;Walker et al., 2020). Adaptation of photosynthesis to external cues has been explored with a focus either on intrinsic aspects of the photochemical process (Alric and Johnson, 2017;Tikhonov and Vershubskii, 2017), or on the dynamic of CO2 assimilation via Rubisco carboxylation/oxygenation (von Caemmerer, 2020).Likewise, primary metabolic responses to environmental factors have usually involved the characterization of enzymatic activities and central metabolites (e.g., Rubisco, sucrose, starch and protein biosynthetic pathways), independently of photosynthetic parameters (Stitt et al., 2010). Research on further metabolic processes, such as glycolysis, TCA cycle or lipid metabolism have also addressed the connection with photosynthesis mostly indirectly, as a downstream proxy of changes seen in photosynthetic yield. This Research Topic offered an opportunity to present work investigating simultaneously photosynthesis and primary metabolism from a novel perspective. To encourage more integrative research, our proposal was designed to explore photosynthetic energy transduction and CO2 assimilation from photosystem I (PSI) point of view. Recent mounting evidence has demonstrated that PSI is a critical point in the photosynthetic machinery to respond against sudden changes in central metabolism and/or growing conditions. This is in part due to simultaneous regulatory roles in both upstream photochemical reactions, through the control of photo-protective mechanisms, and downstream metabolic pathways, including CO2 fixation and redox levels. Furthermore, the sensitivity of PSI to the imbalance between energy production and cell-metabolism demands, a phenomenon called PSI-acceptor side limitation, makes PSI an excellent gauge of non-optimal external conditions. In this research topic, the reader can find a set of articles demonstrating the intimate connection between central metabolism and photosynthetic performance with focus on PSI.The recent advances in the comprehension of the link between plastid fatty acid metabolism and redox status are presented in a mini-review by Hernández and Cejudo (https://www.frontiersin.org/articles/10.3389/fpls.2021.712022). Both the steps of the biosynthetic pathways for de novo fatty-acid production and the role of these molecules in photosynthetic performance and in response to abiotic stress are discussed as part of the chloroplast function. In addition, the authors identified key steps in lipid metabolism regulated by Thioredoxin (Trx)-NADPH-dependent Trx reductase C (NTRC) at the stroma.The latest findings on the molecular mechanisms of PSI photoprotection are exposed by Krämer and Kunz (https://www.frontiersin.org/articles/10.3389/fpls.2021.719003/full). There, they focused on the role of the malate valve as a mechanism of dissipating reducing capacity outside the chloroplast. Their work spotlights not only the stromal NAD(H) as an underappreciated source to mitigate PSI damage, but also the activity of two malate dehydrogenases that explain the generation of NAD(H) in the stroma.Modelling photosynthesis provides a framework to organize and test hypotheses about specific processes experimentally, revealing targets for engineering photosynthesis. Saadat et al. At the light of the positive feedback that we received in this first volume of our Research Topic, we are happy to announce the release of a follow-up issue. With this initiative, we hope to broaden the scope by reaching out for more studies integrating aspects of photosynthesis and metabolism. Please find more info at: https://www.frontiersin.org/research-topics/31418/theback-and-forth-between-metabolism-and-photosystem-i-volume-iiWe are looking forward to your contributions that drive further understanding of the rich and complex operation of photosynthetic organisms.