Unraveling Rubisco packaging within β-carboxysomes.

In this issue of Structure, Kong et al. utilized cryoelectron tomography to closely examine Rubisco packaging within β-carboxysomes. They observed unique Rubisco packaging arrangements that may have important implications for carboxysome structural integrity.

Engineering the cyanobacterial ATP-driven BCT1 bicarbonate transporter for functional targeting to C3 plant chloroplasts.

The ATP-driven bicarbonate transporter 1 (BCT1) from Synechococcus is a four-component complex in the cyanobacterial CO2-concentrating mechanism. BCT1 could enhance photosynthetic CO2 assimilation in plant chloroplasts. However, directing its subunits (CmpA, CmpB, CmpC, and CmpD) to three chloroplast sub-compartments is highly complex.

A carboxysome-based CO concentrating mechanism for C crop chloroplasts: advances and the road ahead.

The introduction of the carboxysome-based CO concentrating mechanism (CCM) into crop plants has been modelled to significantly increase crop yields. This projection serves as motivation for pursuing this strategy to contribute to global food security. The successful implementation of this engineering challenge is reliant upon the transfer of a microcompartment that encapsulates cyanobacterial Rubisco, known as the carboxysome, alongside active bicarbonate transporters.

Plant-based carboxysomes: another step toward increased crop yields.

Synthetically reconstructed carboxysomes form the basis of CO-concentrating mechanisms (CCMs) that could enhance the photosynthetic efficiency of crops and improve yield. Recently, Chen et al. revealed another step toward the reconstruction of bacterial carboxysomes in plants, reporting the formation of almost-complete carboxysomes in the chloroplast of Nicotiana tabacum.

Towards engineering a hybrid carboxysome.

Carboxysomes are bacterial microcompartments, whose structural features enable the encapsulated Rubisco holoenzyme to operate in a high-CO environment. Consequently, Rubiscos housed within these compartments possess higher catalytic turnover rates relative to their plant counterparts. This particular enzymatic property has made the carboxysome, along with associated transporters, an attractive prospect to incorporate into plant chloroplasts to increase future crop yields.

Carboxysome encapsulation of the CO-fixing enzyme Rubisco in tobacco chloroplasts.

A long-term strategy to enhance global crop photosynthesis and yield involves the introduction of cyanobacterial CO-concentrating mechanisms (CCMs) into plant chloroplasts. Cyanobacterial CCMs enable relatively rapid CO fixation by elevating intracellular inorganic carbon as bicarbonate, then concentrating it as CO around the enzyme Rubisco in specialized protein micro-compartments called carboxysomes. To date, chloroplastic expression of carboxysomes has been elusive, requiring coordinated expression of almost a dozen proteins.

Progress and challenges of engineering a biophysical CO2-concentrating mechanism into higher plants.

Growth and productivity in important crop plants is limited by the inefficiencies of the C3 photosynthetic pathway. Introducing CO2-concentrating mechanisms (CCMs) into C3 plants could overcome these limitations and lead to increased yields. Many unicellular microautotrophs, such as cyanobacteria and green algae, possess highly efficient biophysical CCMs that increase CO2 concentrations around the primary carboxylase enzyme, Rubisco, to enhance CO2 assimilation rates.