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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 (CO 2 ) and water, has been hypothesized to play a role in C 3 photosynthesis. We identified two tobacco stromal CAs, β-CA1 and β-CA5, and produced CRISPR/Cas9 mutants affecting their encoding genes. While single knockout lines Δβ - ca1 and Δβ-ca5 had no striking phenotypic differences compared to wild type (WT) plants, Δβ - ca1ca5 leaves developed abnormally and exhibited large necrotic lesions even when supplied with sucrose. Leaf development of Δβ - ca1ca5 plants normalized at 9,000 ppm CO 2 . Leaves of Δβ - ca1ca5 mutants and WT that had matured in high CO 2 had identical CO 2 fixation rates and photosystem II efficiency. Fatty acids, which are formed through reactions with bicarbonate substrates, exhibited abnormal profiles in the chloroplast CA-less mutant. Emerging Δβ - ca1ca5 leaves produce reactive oxygen species in chloroplasts, perhaps due to lower nonphotochemical quenching efficiency compared to WT. Δβ - ca1ca5 seedling germination and development is negatively affected at ambient CO 2 . Transgenes expressing full-length β-CA1 and β-CA5 proteins complemented the Δβ-ca1ca5 mutation 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, while Δβ-ca1 and Δβ-ca1ca5 plants 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 C 3 plant tobacco.  more » « less
Award ID(s):
1642386
PAR ID:
10313019
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
Proceedings of the National Academy of Sciences
Volume:
118
Issue:
33
ISSN:
0027-8424
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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