The article describes an unconventional small subunit of the enzyme Rubisco, which forms the basis of a CO2-concentrating organelle in land plants. This subunit evolved in thermophilic anaerobes and later stabilized the Rubisco complex. The addition of small subunits increased the enzyme's catalytic efficiency fourfold and doubled its specificity for CO2 over oxygen. This development occurred more than 2.4 billion years ago, before cyanobacteria increased the concentration of oxygen in the atmosphere. During the evolution of eukaryotic green algae and land plants, the gene for the small subunit moved from chloroplasts to the cell nucleus. Plants must thus coordinate the expression of genes from both genomes and precisely connect the small and large subunits of the enzyme. A deeper understanding of Rubisco structure and function may help increase crop yields through genetic transformation of chloroplasts.[1]