Pyrenoid-based CO2-concentrating mechanisms across diverse lineages: convergent features and their applications for engineering.

Engineering pyrenoid-based CO2-concentrating mechanisms (pCCMs) into crop plants is a promising strategy to boost photosynthetic performance, enhance yield potential, and improve resilience to future climates. Achieving this goal requires a deeper understanding of the molecular principles that enable pyrenoids to elevate CO2 around Rubisco. Although pyrenoids span a remarkable diversity of forms across algae and hornworts, they consistently exhibit three core features: a condensed Rubisco matrix, specialised membranes that deliver inorganic carbon, and a diffusion barrier that restricts CO2 leakage. Here, we review recent mechanistic advances from Chlamydomonas reinhardtii alongside emerging insights from other algae and hornworts that highlight both conserved strategies and lineage-specific innovations in Rubisco condensation, membrane-associated inorganic carbon channelling, and matrix encapsulation. Together, these findings refine our understanding of pCCM diversity and provide an increasingly robust blueprint for reconstructing pCCMs in vascular plant chloroplasts.