Functional Incorporation of Sorghum Small Subunit Increases the Catalytic Turnover Rate of Rubisco in Transgenic Rice

• Published in: Plant physiology (Bethesda) Vol. 156; no. 3; pp. 1603 - 1611
• Main Authors: Ishikawa, Chie, Hatanaka, Tomoko, Misoo, Shuji, Miyake, Chikahiro, Fukayama, Hiroshi
• Format: Journal Article
• Language: English
• Published: Rockville, MD American Society of Plant Biologists 01-07-2011
• Subjects: Agronomy. Soil science and plant productions; Amino acids; Biocatalysis; BIOENERGETICS AND PHOTOSYNTHESIS; Biological and medical sciences; C3 plants; Chlorophyll - metabolism; Chlorophylls; Enzyme Activation; Fundamental and applied biological sciences. Psychology; Genetic engineering applications; Genetics and breeding of economic plants; Kinetics; Leaves; Molecular Sequence Data; Oryza - genetics; Oryza - growth & development; Oryza sativa; Photosynthesis; Plant breeding: fundamental aspects and methodology; Plant physiology and development; Plant Proteins - metabolism; Plants; Plants, Genetically Modified; Ribulose-Bisphosphate Carboxylase - metabolism; Rice; Solubility; Sorghum; Sorghum - enzymology; Sorghum bicolor; Transgenic plants; Monocotyledones; Enzyme; Ribulose-bisphosphate carboxylase; Sorghum; Lyases; Subunit; Carbon-carbon lyases; Oryza; Plant physiology; Gramineae; Carboxy-lyases; Angiospermae; Turnover; Herbaceous plant; Spermatophyta; Transgenic plant; Catalysis
• ISSN: 0032-0889; 1532-2548; 1532-2548
• DOI: 10.1104/pp.111.177030

Rubisco limits photosynthetic CO₂ fixation because of its low catalytic turnover rate (k
cat
) and competing oxygenase reaction. Previous attempts to improve the catalytic efficiency of Rubisco by genetic engineering have gained little progress. Here we demonstrate that the introduction of the small subunit (RbcS) of high k
cat
Rubisco from the C₄ plant sorghum (Sorghum bicolor) significantly enhances k
cat
of Rubisco in transgenic rice (Oryza sativa). Three independent transgenic lines expressed sorghum RbcS at a high level, accounting for 30%, 44%, and 79% of the total RbcS. Rubisco was likely present as a chimera of sorghum and rice RbcS, and showed 1.32-to 1.50-fold higher k
cat
than in nontransgenic rice. Rubisco from transgenic lines showed a higher K
m
for CO₂ and slightly lower specificity for CO₂ than nontransgenic controls. These results suggest that Rubisco in rice transformed with sorghum RbcS partially acquires the catalytic properties of sorghum Rubisco. Rubisco content in transgenic lines was significantly increased over wild-type levels but Rubisco activation was slightly decreased. The expression of sorghum RbcS did not affect CO₂ assimilation rates under a range of CO₂ partial pressures. The J
max
/V
cmax
ratio was significantly lower in transgenic line compared to the nontransgenic plants. These observations suggest that the capacity of electron transport is not sufficient to support the increased Rubisco capacity in transgenic rice. Although the photosynthetic rate was not enhanced, the strategy presented here opens the way to engineering Rubisco for improvement of photosynthesis and productivity in the future.