Year: 2025
Type: article
Abstract: Photosynthesis is the primary process by which plants harness the energy of sunlight to convert water and carbon dioxide into energy-rich organic compounds. These compounds serve as the foundation for all food chains on the planet. Moreover, photosynthesis plays a vital role in the global carbon cycle, as photosynthetic organisms help regulate the Earth’s climate by sequestering carbon and reducing greenhouse gas concentrations. Photosynthesis is a complex trait determined by numerous component traits that are themselves multigenic. Understanding the intricacies of photosynthesis is crucial in developing strategies to improve crop productivity, support sustainable agricultural practices, and mitigate the impacts of climate change. The Journal of Experimental Botany (JXB) has a long history of publishing impactful research in this field, evident even in the first issue of the journal in March 1950 with an advance in understanding the ‘path of carbon in photosynthesis’ by Andrew Benson and Melvin Calvin (Benson and Calvin, 1950) (Fig. 1). The journal continues to publish high-quality and important photosynthesis research, and this Virtual Issue focuses on recent progress in revealing the intricacies of photosynthesis. It brings together a collection of manuscripts that exemplify innovative advances in technology and research, showcasing our understanding of the complex mechanisms, adaptations, and environmental influences that govern photosynthesis. A photograph of the front cover of the first issue of the Journal of Experimental Botany, published in March 1950. In 2020, JXB introduced a new type of paper dedicated to the communication of new and improved research methods. The first of these Technical Innovations was an analysis of plate-based methods for measuring Rubisco activity (Sales et al., 2020). Given the importance of Rubisco in photosynthesis, the provision of cost-effective, reliable, and simple alternatives to the traditional radiometric assays is vital to the photosynthetic research effort. Since 2020, the journal has published many more method advances related to photosynthesis. Some of these have sought to update well-established methods, for example: a revision to the steady-state model of C4 photosynthesis (von Caemmerer, 2021); a correction to the PSI quantum yield equation, demonstrating that the previously reported seasonal up-regulation of cyclic electron transfer (CET) during spring recovery of photosynthesis in boreal conifers is in fact absent (Grebe et al., 2024); and modification of the ‘one-point method’ enabling accurate estimation of the maximum carboxylation rate of Rubisco at higher temperatures (Oliveira et al., 2023). Other methods have improved the efficiency of photosynthesis research, for example through the continued development of an Escherichia coli-based expression system for testing heterologous Rubisco production in planta (Buck et al., 2023), and the demonstration that the Dynamic Assimilation Technique (DAT) can reduce the measurement time of A/Ci curves by almost a half without loss of accuracy compared with conventional steady-state methods (Tejera-Nieves et al., 2024). Ferguson et al. (2023) established differences in measured photosynthetic traits between excised and attached leaves across three crop species, an important observation for photosynthesis researchers performing similar experiments. Embracing an exciting and developing technology, two groups independently reviewed the use of artificial intelligence and machine learning for rapid and robust stomatal phenotyping, highlighting the current capabilities, limitations, and future directions for the technology (Gibbs and Burgess, 2024; Tan et al., 2024), while another group used machine learning to predict Rubisco kinetics (Iqbal et al., 2023). Characterizing the genetic diversity of photosynthetic traits, both within and between species, can help us to better understand photosynthetic mechanisms. It also provides a valuable resource to identify potential targets to modulate aspects of photosynthesis for various applications. In their study, Gao et al. (2024) screened 23 field-grown inbred barley lines by measuring chlorophyll fluorescence and growth traits, identifying genetic variation in photosynthetic parameters that correlated with yield. The development of a high-throughput screening method was also used in identifying exploitable genetic variation in bread wheat (Faralli et al., 2024). In this case, combining gas exchange and thermal imaging revealed significant variation in photosynthetic and stomatal traits among bread wheat genotypes, including CO2 uptake rates, stomatal dynamics, and evaporative cooling. Another impressive example is the high-throughput phenotyping of African and Asian rice accessions for photosynthetic heat tolerance, focusing primarily on the heat-sensitive PSII complex followed by genome-wide association studies (Robson et al., 2023). This approach identified 133 candidate genes for improving photosynthesis under high temperature, paving the way for breeding heat-tolerant rice varieties. Using both glasshouse and field phenotyping, an analysis of 178 climbing bean lines was also successful in exploring variation in photosynthetic efficiency to identify a potential target to boost yield (Keller et al., 2024). Fluctuating light can disrupt the balance of ATP and NADPH production and consumption in photosynthesis, leading to damaging oxidative stress. A symptom of such conditions is the oscillation of CO2 assimilation and fluorescence parameters. Impairment of Proton Gradient Regulation 5 (PGR5)-dependent CET heightened these oscillations, identifying a major role for this protein in dampening photosynthetic stress during environmental fluctuations (Degen et al., 2024). Employing DATs, further research into the underlying mechanics of such oscillations provided crucial insight into how they respond to triose phosphate utilization (TPU) and changes in CO2 concentration, deepening our understanding of the dynamic behaviour of photosynthesis (McClain and Sharkey, 2023). When excess light is absorbed by the photosynthetic machinery, plants may experience photoinhibition if photoprotective systems cannot repair the damage rapidly enough. To date, the majority of research into photoinhibition has been conducted in photosynthetic organisms that are not particularly tolerant to high light. Levin and Schuster (2024) argue eloquently that photoprotection should be studied predominantly in high-light-tolerant species to better identify and characterize efficient protective mechanisms. As well as studying the response of photosynthesis to changing light conditions at the organellar scale, significant advances have been made in recent years in our knowledge of how photosynthesis responds at the canopy scale (reviewed in Sellaro et al., 2025). A recent example of this is a study of leaves from different positions in mature tomato canopies (Shao et al., 2024). Leaves at the top of the canopy were faster to adjust photosynthesis and photoprotective systems in response to changing light than leaves from lower in the canopy. A model analysis of the canopy-level data revealed that a single set of parameters was sufficient to predict whole-canopy assimilation under fluctuating light. The threat of climate change looks set to present future crops with higher atmospheric CO2 concentrations, warmer temperatures, and unpredictable weather events. Consequently, considerable research effort is invested in understanding how plants might fare under such conditions, especially in response to high temperature stress (reviewed by Moore et al., 2021; Qu et al., 2023). In Arabidopsis, Cavanagh et al. demonstrate that differential expression of Rubisco small subunits in response to high temperature produces Rubisco protein with an enhanced carboxylation capacity, sufficient to compensate for a concomitant reduction in Rubisco content at higher temperatures (Cavanagh et al., 2023). Another study looked at the photosynthetic responses of wheat genotypes to warm nights, and found that night-time warming directly impacted wheat photosynthesis and its acclimation ability, with distinct responses between newly formed and pre-existing leaves (Coast et al., 2024). Al-Salman et al. (2023) looked at the combined effects of elevated CO2 (eCO2), high temperature, and water stress on photosynthesis in the C4 crop sorghum, revealing leaf stomatal conductance as the central player in a trade-off between improving water use efficiency and maintaining adequate thermoregulation. The intersection of eCO2 and unfavourable climatic conditions was further probed by Ancín et al. (2024) who showed that photosynthesis is boosted by eCO2 in C3 and C4 plants, although the carboxylation rate and Rubisco activity were reduced in C3 species. These responses were largely unmodified by drought or heat stress, providing further insight into how photosynthesis may be affected by a changing climate. The majority of plants employ C3 photosynthesis to fix carbon, but other types of photosynthesis have evolved that concentrate CO2 around Rubisco to inhibit its oxygenation reaction and increase carboxylation. These include biochemical carbon-concentrating mechanisms (CCMs) such as C4 and Crassulacean acid metabolism (CAM) photosynthesis, as well as biophysical CCMs such as the cyanobacterial carboxysome and the algal pyrenoid. Research to advance our understanding of these other forms of photosynthesis may hold the key for engineering C3 crops with improved photosynthetic efficiency. Schlüter et al. (2023) performed a phylogenetic analysis of the C3–C4 intermediate phenotype in Brassicaceae species, revealing that it has evolved up to five times independently in this plant family, with varying efficiency. The convergent evolution of this feature suggests that it is beneficial under certain environmental conditions and may be a good target for transfer to C3 Brassicaceae crops to improve their metabolic plasticity under a dynamic climate. Another study used a 3D maize leaf model to predict how chloroplast movement might affect C4 photosynthesis (Retta et al., 2023). The movement of chloroplasts towards mesophyll cells increased light absorption and photosynthetic rates, while the converse was true for chloroplast avoidance movement (away from bundle sheath cells), an important insight when attempting to engineer C4 photosynthesis into C3 crops. Staying in maize, Eshenour et al. (2024) further probed the opportunities for boosting C4 photosynthesis through increased expression of Rubisco subunits and assembly factors. Turning attention to the biophysical CCMs, the Chlamydomonas LCIA protein has long been considered a membrane bicarbonate transporter in the algal CCM. This was finally demonstrated for the first time by expressing LCIA in mutant bacterial and plant systems which are normally unable to grow in ambient CO2 (Förster et al., 2023). LCIA expression rescued growth in both systems, indicating that LCIA was enabling bicarbonate uptake, confirming it as a crucial component of the algal CCM. The BCT1 bicarbonate transporter is a complex of the cyanobacterial CCM that holds promise for engineering improved photosynthetic efficiency in C3 plants. However, correct targeting of the four components to the correct chloroplast locations is extremely challenging. A rational design and directed evolution approach yielded constitutively active versions of BCT1, although none was able to boost photosynthesis in planta (Rottet et al., 2024). However, this type of modification of CCM components does represent a viable strategy for improving plant photosynthesis. Rubisco and its Regulation (2023): https://academic.oup.com/jxb/issue/74/2. Edited by Elizabete Carmo-Silva and Rob Sharwood. Stomata—Gatekeepers to Future Plant Performance (2024): https://academic.oup.com/jxb/issue/75/21. Edited by Andrew Leakey and Tracy Lawson. The exploration of photosynthesis continues to unfold, shaping our understanding and our ability to tackle global challenges. This JXB Virtual Issue serves as a platform to celebrate the exciting progress made in both unravelling its complexities and translating that knowledge to address global challenges. We hope the research described here can inspire further exploration, collaboration, and innovation in photosynthesis research to unlock the potential of this fundamental process and chart a path towards a greener and more sustainable world. The author(s) declare no conflicts of interest.
Source: Journal of Experimental Botany
DOI: 10.1093/jxb/eraf096
Authors: Mike T Page, Martin A J Parry
Institution: Lancaster University
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
SDGs: Climate action, Zero hunger
Open Access status: hybrid
Estimated APC paid: $4,341
OpenAlex ID: W4410430865