More Like this

1. Indirect Export of Reducing Equivalents From the Chloroplast to Resupply NADP for C3 Photosynthesis—Growing Importance for Stromal NAD(H)?

   https://doi.org/10.3389/fpls.2021.719003  

   Krämer, Moritz ; Kunz, Hans-Henning ( October 2021 , Frontiers in Plant Science)

   Plant productivity greatly relies on a flawless concerted function of the two photosystems (PS) in the chloroplast thylakoid membrane. While damage to PSII can be rapidly resolved, PSI repair is complex and time-consuming. A major threat to PSI integrity is acceptor side limitation e.g., through a lack of stromal NADP ready to accept electrons from PSI. This situation can occur when oscillations in growth light and temperature result in a drop of CO 2 fixation and concomitant NADPH consumption. Plants have evolved a plethora of pathways at the thylakoid membrane but also in the chloroplast stroma to avoid acceptor side limitation. For instance, reduced ferredoxin can be recycled in cyclic electron flow or reducing equivalents can be indirectly exported from the organelle via the malate valve, a coordinated effort of stromal malate dehydrogenases and envelope membrane transporters. For a long time, the NADP(H) was assumed to be the only nicotinamide adenine dinucleotide coenzyme to participate in diurnal chloroplast metabolism and the export of reductants via this route. However, over the last years several independent studies have indicated an underappreciated role for NAD(H) in illuminated leaf plastids. In part, it explains the existence of the light-independent NAD-specific malate dehydrogenase in the stroma. We review the history of the malate valve and discuss the potential role of stromal NAD(H) for the plant survival under adverse growth conditions as well as the option to utilize the stromal NAD(H) pool to mitigate PSI damage. 

   more » « less
2. The Arabidopsis T‐DNA mutant SALK_008491 carries a 14‐kb deletion on chromosome 3 that provides rare insights into the plant response to dynamic light stress

   https://doi.org/10.1002/pld3.429  

   Lopez, Laura S. ; Völkner, Carsten ; Day, Philip M. ; Lewis, Chance M. ; Lewis, Chase L. ; Schneider, Dominik ; Correa Galvis, Viviana ; Cruz, Jeffrey A. ; Armbruster, Ute ; Kramer, David M. ; et al ( July 2022 , Plant Direct)

   In nature, plants experience rapid changes in light intensity and quality throughout the day. To maximize growth, they have established molecular mechanisms to optimize photosynthetic output while protecting components of the light‐dependent reaction and CO₂fixation pathways. Plant phenotyping of mutant collections has become a powerful tool to unveil the genetic loci involved in environmental acclimation. Here, we describe the phenotyping of the transfer‐DNA (T‐DNA) insertion mutant line SALK_008491, previously known asnhd1‐1. Growth in a fluctuating light regime caused a loss in growth rate accompanied by a spike in photosystem (PS) II damage and increased non‐photochemical quenching (NPQ). Interestingly, an independentnhd1null allele did not recapitulate the NPQ phenotype. Through bulk sequencing of a backcrossed segregating F₂pool, we identified an ~14‐kb large deletion on chromosome 3 (Chr3) in SALK_008491 affecting five genes upstream ofNHD1. BesidesNHD1, which encodes for a putative plastid Na⁺/H⁺antiporter, the stromal NAD‐dependent D‐3‐phosphoglycerate dehydrogenase 3 (PGDH3) locus was eradicated. Although some changes in the SALK_008491 mutant's photosynthesis can be assigned to the loss of PGDH3, our follow‐up studies employing respective single mutants and complementation with overlapping transformation‐competent artificial chromosome (TAC) vectors reveal that the exacerbated fluctuating light sensitivity in SALK_008491 mutants result from the simultaneous loss of PGDH3 and NHD1. Altogether, the data obtained from this large deletion‐carrying mutant provide new and unintuitive insights into the molecular mechanisms that function to protect the photosynthetic machinery. Moreover, our study renews calls for caution when setting up reverse genetic studies using T‐DNA lines. Although second‐site insertions, indels, and SNPs have been reported before, large deletion surrounding the insertion site causes yet another problem. Nevertheless, as shown through this research, such unpredictable genetic events following T‐DNA mutagenesis can provide unintuitive insights that allow for understanding complex phenomena such as the plant acclimation to dynamic high light stress.

    

   more » « less
3. The redox code of plants

   https://doi.org/10.1111/pce.14787  

   Mittler, Ron ; Jones, Dean P. ( December 2023 , Plant, Cell & Environment)

   Central metabolism is organised through high‐flux, Nicotinamide Adenine Dinucleotide (NAD⁺/NADH) and NADP⁺/NADPH systems operating at near equilibrium. As oxygen is indispensable for aerobic organisms, these systems are also linked to the levels of reactive oxygen species, such as H₂O₂, and through H₂O₂to the regulation of macromolecular structures and activities, via kinetically controlled sulphur switches in the redox proteome. Dynamic changes in H₂O₂production, scavenging and transport, associated with development, growth and responses to the environment are, therefore, linked to the redox state of the cell and regulate cellular function. These basic principles form the ‘redox code’ of cells and were first defined by D. P. Jones and H. Sies in 2015. Here, we apply these principles to plants in which recent studies have shown that they can also explain cell‐to‐cell and even plant‐to‐plant signalling processes. The redox code is, therefore, an integral part of biological systems and can be used to explain multiple processes in plants at the subcellular, cellular, tissue, whole organism and perhaps even community and ecosystem levels. As the environmental conditions on our planet are worsening due to global warming, climate change and increased pollution levels, new studies are needed applying the redox code of plants to these changes.

    

   more » « less
4. 2 H/ 1 H variation in microbial lipids is controlled by NADPH metabolism

   https://doi.org/10.1073/pnas.1818372116  

   Wijker, Reto S. ; Sessions, Alex L. ; Fuhrer, Tobias ; Phan, Michelle ( June 2019 , Proceedings of the National Academy of Sciences)

   null (Ed.)

   The hydrogen-isotopic compositions ( 2 H/ 1 H ratios) of lipids in microbial heterotrophs are known to vary enormously, by at least 40% (400‰) relative. This is particularly surprising, given that most C-bound H in their lipids appear to derive from the growth medium water, rather than from organic substrates, implying that the isotopic fractionation between lipids and water is itself highly variable. Changes in the lipid/water fractionation are also strongly correlated with the type of energy metabolism operating in the host. Because lipids are well preserved in the geologic record, there is thus significant potential for using lipid 2 H/ 1 H ratios to decipher the metabolism of uncultured microorganisms in both modern and ancient ecosystems. But despite over a decade of research, the precise mechanisms underlying this isotopic variability remain unclear. Differences in the kinetic isotope effects (KIEs) accompanying NADP + reduction by dehydrogenases and transhydrogenases have been hypothesized as a plausible mechanism. However, this relationship has been difficult to prove because multiple oxidoreductases affect the NADPH pool simultaneously. Here, we cultured five diverse aerobic heterotrophs, plus five Escherichia coli mutants, and used metabolic flux analysis to show that 2 H/ 1 H fractionations are highly correlated with fluxes through NADP + -reducing and NADPH-balancing reactions. Mass-balance calculations indicate that the full range of 2 H/ 1 H variability in the investigated organisms can be quantitatively explained by varying fluxes, i.e., with constant KIEs for each involved oxidoreductase across all species. This proves that lipid 2 H/ 1 H ratios of heterotrophic microbes are quantitatively related to central metabolism and provides a foundation for interpreting 2 H/ 1 H ratios of environmental lipids and sedimentary hydrocarbons. 

   more » « less
5. Absence of carbonic anhydrase in chloroplasts affects C 3 plant development but not photosynthesis

   https://doi.org/10.1073/pnas.2107425118  

   Hines, Kevin M. ; Chaudhari, Vishalsingh ; Edgeworth, Kristen N. ; Owens, Thomas G. ; Hanson, Maureen R. ( August 2021 , Proceedings of the National Academy of Sciences)

   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.

    

   more » « less