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Summary Plants integrate environmental stimuli to optimize photosynthesis vs water loss by controlling stomatal apertures. However, stomatal responses to temperature elevation and the underlying molecular genetic mechanisms remain less studied.We developed an approach for clamping leaf‐to‐air vapor pressure difference (VPDleaf) to fixed values, and recorded robust reversible warming‐induced stomatal opening in intact plants. We analyzed stomatal temperature responses of mutants impaired in guard cell signaling pathways for blue light, abscisic acid (ABA), CO2, and the temperature‐sensitive proteins, Phytochrome B (phyB) and EARLY‐FLOWERING‐3 (ELF3).We confirmed thatphot1‐5/phot2‐1leaves lacking blue‐light photoreceptors showed partially reduced warming‐induced stomatal opening. Furthermore, ABA‐biosynthesis, phyB, and ELF3 were not essential for the stomatal warming response. Strikingly,Arabidopsis(dicot) andBrachypodium distachyon(monocot) mutants lacking guard cell CO2sensors and signaling mechanisms, includinght1,mpk12/mpk4‐gc, andcbc1/cbc2abolished the stomatal warming response, suggesting a conserved mechanism across diverse plant lineages. Moreover, warming rapidly stimulated photosynthesis, resulting in a reduction in intercellular (CO2). Interestingly, further enhancing heat stress caused stomatal opening uncoupled from photosynthesis.We provide genetic and physiological evidence that the stomatal warming response is triggered by increased CO2assimilation and stomatal CO2sensing. Additionally, increasing heat stress functions via a distinct photosynthesis‐uncoupled stomatal opening pathway.
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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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- Award ID(s):
- 1642386
- PAR ID:
- 10286431
- Publisher / Repository:
- Proceedings of the National Academy of Sciences
- Date Published:
- Journal Name:
- Proceedings of the National Academy of Sciences
- Volume:
- 118
- Issue:
- 33
- ISSN:
- 0027-8424
- Page Range / eLocation ID:
- Article No. e2107425118
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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