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This article comments on: Archer J, Kathpalia M, Lee B, Li S, Wang T. 2025. Effects of chaperone selectivity on the assembly of plant Rubisco orthologs in E. coli. Journal of Experimental Botany 76, 2809–2820 https://doi.org/10.1093/jxb/eraf140 

ABSTRACT Pyrenoid-based CO₂-concentrating mechanisms (pCCMs) turbocharge photosynthesis by saturating CO₂around Rubisco. Hornworts are the only land plants with a pCCM. Owing to their closer relationship to crops, hornworts could offer greater translational potential compared to the green alga Chlamydomonas, the traditional model for studying pCCM. Here we report the first thorough investigation of a hornwort pCCM using the emerging modelAnthoceros agrestis. The pyrenoids inA. agrestisexhibit liquid-like properties similar to Chlamydomonas, but differ by lacking starch sheaths and being enclosed by multiple thylakoids. We found that the core pCCM components in Chlamydomonas, including BST, LCIB, and CAH3, are conserved inA. agrestisand likely have similar functions based on their subcellular localizations. Therefore, the underlying chassis for concentrating CO₂might be shared between hornworts and Chlamydomonas, and ancestral to land plants. Our study presents the first spatial model for pCCM in a land plant, paving the way for future biochemical and genetic investigations. 

Abstract Nature’s vital, but notoriously inefficient, CO2-fixing enzyme Rubisco often limits the growth of photosynthetic organisms including crop species. Form I Rubiscos comprise eight catalytic large subunits and eight auxiliary small subunits and can be classified into two distinct lineages—‘red’ and ‘green’. While red-type Rubiscos (Form IC and ID) are found in rhodophytes, their secondary symbionts, and certain proteobacteria, green-type Rubiscos (Form IA and IB) exist in terrestrial plants, chlorophytes, cyanobacteria, and other proteobacteria. Eukaryotic red-type Rubiscos exhibit desirable kinetic properties, namely high specificity and high catalytic efficiency, with certain isoforms outperforming green-type Rubiscos. However, it is not yet possible to functionally express a high-performing red-type Rubisco in chloroplasts to boost photosynthetic carbon assimilation in green plants. Understanding the molecular and evolutionary basis for divergence between red- and green-type Rubiscos could help us to harness the superior CO2-fixing power of red-type Rubiscos. Here we review our current understanding about red-type Rubisco distribution, biogenesis, and sequence–structure, and present opportunities and challenges for utilizing red-type Rubisco kinetics towards crop improvements.