Abstract
Summary Introducing components of algal carbon concentrating mechanisms (CCMs) into higher plant chloroplasts could increase photosynthetic productivity. A key component is the Rubisco‐containing pyrenoid that is needed to minimise CO 2 retro‐diffusion for CCM operating efficiency.Rubisco in Arabidopsis was re‐engineered to incorporate sequence elements that are thought to be essential for recruitment of Rubisco to the pyrenoid, namely the algal Rubisco small subunit (SSU, encoded by rbcS) or only the surface‐exposed algal SSU α‐helices.Leaves of Arabidopsis rbcs mutants expressing ‘pyrenoid‐competent’ chimeric Arabidopsis SSUs containing the SSU α‐helices from Chlamydomonas reinhardtii can form hybrid Rubisco complexes with catalytic properties similar to those of native Rubisco, suggesting that the α‐helices are catalytically neutral.The growth and photosynthetic performance of complemented Arabidopsis rbcs mutants producing near wild‐type levels of the hybrid Rubisco were similar to those of wild‐type controls. Arabidopsis rbcs mutants expressing a Chlamydomonas SSU differed from wild‐type plants with respect to Rubisco catalysis, photosynthesis and growth. This confirms a role for the SSU in influencing Rubisco catalytic properties.
Highlights
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) catalyses net CO2 23 assimilation in all photosynthetic organisms
We have shown that heterologous, pyrenoid competent SSUs assemble with the native LSU to produce a functional hybrid Rubisco with 368 catalytic properties similar to the native Rubisco
Four genotypes provided data that lead to this conclusion: (i) wild-type plants, with the highest Rubisco content and with Rubisco containing almost exclusively rbcS1A, rbcS2B and rbcS3B SSUs; (ii) 1AAt plants, with about 78% of wild-type Rubisco content and with Rubisco containing mainly rbcS1A and rbcS2B; (iii) the 1a2b mutant, with 45% of wild-type Rubisco content and with Rubisco containing mainly rbcS3B, and (iv) the 1a3b mutant, with 30% of wild-type Rubisco content and with Rubisco containing rbcS2B
Summary
Introducing components of algal carbon concentrating mechanisms (CCMs) into higher plant chloroplasts could increase photosynthetic productivity. A key component is the Rubisco-containing pyrenoid that is needed to minimise CO2 retrodiffusion for CCM operating efficiency. Rubisco in Arabidopsis was re-engineered to incorporate sequence elements which are thought be essential for recruitment of Rubisco to the pyrenoid, viz the algal. The growth and photosynthetic performance of complemented Arabidopsis rbcs mutants producing near wild-type levels of the hybrid Rubisco were similar to those of wild-type controls. Arabidopsis rbcs mutants expressing the Chlamydomonas SSU differed from wildtype plants with respect to Rubisco catalysis, photosynthesis and growth. This confirms a role for the SSU in influencing Rubisco catalytic properties
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