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Title: Absence of carbonic anhydrase in chloroplasts affects C 3 plant development but not photosynthesis

The enzyme carbonic anhydrase (CA), which catalyzes the interconversion of bicarbonate with carbon dioxide (CO2) and water, has been hypothesized to play a role in C3photosynthesis. We identified two tobacco stromal CAs, β-CA1 and β-CA5, and produced CRISPR/Cas9 mutants affecting their encoding genes. While single knockout linesΔβ-ca1andΔβ-ca5had no striking phenotypic differences compared to wild type (WT) plants,Δβ-ca1ca5leaves developed abnormally and exhibited large necrotic lesions even when supplied with sucrose. Leaf development ofΔβ-ca1ca5plants normalized at 9,000 ppm CO2. Leaves ofΔβ-ca1ca5mutants and WT that had matured in high CO2had identical CO2fixation rates and photosystem II efficiency. Fatty acids, which are formed through reactions with bicarbonate substrates, exhibited abnormal profiles in the chloroplast CA-less mutant. EmergingΔβ-ca1ca5leaves produce reactive oxygen species in chloroplasts, perhaps due to lower nonphotochemical quenching efficiency compared to WT.Δβ-ca1ca5seedling germination and development is negatively affected at ambient CO2. Transgenes expressing full-length β-CA1 and β-CA5 proteins complemented theΔβ-ca1ca5mutation but inactivated (ΔZn-βCA1) and cytoplasm-localized (Δ62-βCA1) forms of β-CA1 did not reverse the growth phenotype. Nevertheless, expression of the inactivated ΔZn-βCA1 protein was able to restore the hypersensitive response to tobacco mosaic virus, whileΔβ-ca1andΔβ-ca1ca5plants failed to show a hypersensitive response. We conclude that stromal CA plays a role in plant development, likely through providing bicarbonate for biosynthetic reactions, but stromal CA is not needed for maximal rates of photosynthesis in the C3plant tobacco.

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Publisher / Repository:
Proceedings of the National Academy of Sciences
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Proceedings of the National Academy of Sciences
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Article No. e2107425118
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National Science Foundation
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