The “Photosynthetic C1 Pathway” Links Carbon Assimilation and Growth in Plants

The Science

This research unveils a highly active “photosynthetic one-carbon (C₁) pathway” in poplar trees—crucial for plant growth and potentially widespread across the plant kingdom, suggesting an evolutionary origin in cyanobacteria. This pathway may be a fundamental mechanism in the “carbon dioxide (CO₂) fertilization” response of the biosphere, evolving alongside oxygenic photosynthesis to boost plant productivity, especially under elevated CO₂ conditions.

In the presence of light, C₁ photosynthesis is driven by RuBisCO—the same enzyme behind the Calvin-Benson cycle. While the Calvin cycle focuses on three-carbon (C₃) intermediates, C₁ photosynthesis goes further, integrating CO₂ with sulfate and ammonia assimilation directly into amino acids. This paper describes the process like a soccer game, where RuBisCO continuously “passes the ball” (carbon atoms) to enzymes that work together to “score goals” by attaching these carbon atoms to vital growth compounds.

The Impact

The discovery of an active C₁ photosynthesis pathway in plants may resolve the long-standing controversy about plant methane production and explain the large carbon-13 (¹³C) anomaly observed in C₁ carbon pools over 2 decades ago. Additionally, the study predicts an upregulation of C₁ photosynthesis and nutrient assimilation with elevated CO₂ as a potentially key mechanism facilitating the “CO₂ fertilization” of the biosphere. Given its critical importance for growth, genetic engineering of the photosynthetic C₁ pathway could significantly enhance plant productivity.

Summary

Although primarily studied in relation to photorespiration, serine metabolism in chloroplasts may play a key role in plant CO₂ fertilization responses by linking CO₂ assimilation with growth. Here, a team of researchers show the phosphorylated serine pathway is part of a “photosynthetic C₁ pathway” and demonstrate its high activity in foliage of a C₃ tree where it rapidly integrates photosynthesis and C₁ metabolism contributing to new biomass via methyl transfer reactions, imparting a large natural ¹³C-depleted signature.

Using ¹³CO₂-labeling, researchers show leaf serine, the S-methyl group of leaf methionine, pectin methyl esters, and the associated methanol released during cell wall expansion during growth are directly produced from photosynthetically linked C₁ metabolism within minutes of light exposure. The team speculates the photosynthetic C₁ pathway is highly conserved across the photosynthetic tree of life, is responsible for synthesis of the greenhouse gas methane, and may have evolved with oxygenic photosynthesis by providing a mechanism of directly linking carbon and ammonia assimilation with growth.

Although the rise in atmospheric CO₂ inhibits major metabolic pathways like photorespiration, results suggest the photosynthetic C₁ pathway may accelerate and represent a missing link between enhanced photosynthesis and plant growth rates during CO₂ fertilization under a changing climate.

Principal Investigator

Kolby Jardine
Lawrence Berkeley National Laboratory
[email protected]

Program Manager

Brian Benscoter
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
[email protected]

Funding

This research was supported by the U.S. Department of Energy (DOE) Office of Science, Biological and Environmental Research (BER) program, Biological Systems Science Division, Early Career Research Program under Award number FP00007421. Additional DOE funding for the research came from the Next-Generation Ecosystem Experiments Tropics (NGEE Tropics) through contract no. DE-AC02-05CH11231 as part of DOE’s Environmental System Science program. The metabolomics analysis was supported by BER’s Microbial Community Analysis and Functional Evaluation in Soils ([email protected]), a science focus area at Lawrence Berkeley National Laboratory funded by DE-AC02-05CH11231. Support from Brazil was provided from the Brazilian National Council for Scientific and Technological Development (CNPq) grant 312589/2022-0 (Bolsa de produtividade em Pesquisa) and AUSPIN Edital 001/2022—Programa de Bolsas de Intercâmbio Internacional.

Related Links

• The Global Photosynthetic C₁ Pathway and Plant Growth [Animation]
• Researchers Uncover a Hidden Carbon Pathway in Photosynthesis

References