Biology subjects

Sharkey, T. D.

Publications and source records attributed to Sharkey, T. D..

10 recordsLinked to original sources

bioRxiv2026

Extreme cooling enables survival in extreme heat

Complex, multicellular extremophiles face intense challenges in coordinating their cells, tissues, and organs to function in harsh environments. Tidestromia oblongifolia is a desert plant that thrives in Death Valley, where air temperatures exceed 49 {degrees}C. Using natural collections of T. oblongifolia seed, we identified individuals that survive in daily air temperature regimens at the eukaryotic upper thermal limit of 60 {degrees}C. Genome-wide association testing detected genetic variation for survival in extreme heat, and transcriptomics implicated pathways regulating leaf cooling. High-throughput infrared imaging revealed that survival was enabled by leaf cooling far below air temperature, identifying a physiological mechanism of thermophily in a multicellular organism. These discoveries provide insights into mechanisms of extreme heat adaptation that could be leveraged to engineer heat-resilient crops.

plant biology↗

bioRxiv2024

Isoprene deters insect herbivory by priming plant hormone responses

Isoprene, emitted by some plants, enhances plant abiotic resilience but its role in biotic stress resilience remains elusive. We used tobacco plants engineered to emit isoprene (IE) and the corresponding azygous non-emitting control (NE) to investigate isoprene emission and biotic stress resilience. IE plants were more resistant to insect herbivory than NE plants. Worms preferred to feed on NE rather than IE leaves. IE plants showed less decline in photosynthesis during worm feeding. Insect feeding increased jasmonate levels in IE leaves, suggesting isoprene-mediated priming of the jasmonic acid response. Wound-induced increase in isoprene emission corresponded with elevation of methyl-D-erythritol-4-phosphate pathway and Calvin-Benson cycle metabolites. The results highlight interactive functions of isoprene and jasmonic acid and advance our understanding of how isoprene emission enhances plant resilience.

plant biology↗

bioRxiv2024

The effect of constitutive root isoprene emission on root phenotype and physiology under control and salt stress conditions

ABSTRACTIsoprene, a volatile hydrocarbon, is typically emitted from the leaves and other aboveground plant organs; isoprene emission from roots is not well studied. Given its well-known function in plant growth and defense aboveground, isoprene may also be involved in shaping root physiology to resist belowground stress. We used isoprene-emitting transgenic lines (IE) and a non-emitting empty vector and/or wild type lines (NE) of Arabidopsis to elucidate the roles of isoprene in root physiology and salt stress resistance. We assessed root phenotype and metabolic changes, hormone biosynthesis and signaling, and stress-responses under normal and saline conditions of IE and NE lines. We also analyzed the root transcriptome in the presence or absence of salt stress. IE lines emitted isoprene from roots, which was associated with higher primary root growth, root biomass, and root/shoot biomass ratio under both control and salt stress conditions. Transcriptome data indicated that isoprene altered the expression of key genes involved in hormone metabolism and plant responses to stress factors. Our findings reveal that root constitutive isoprene emission sustains root growth also under salinity by regulating and/or priming hormone biosynthesis and signaling mechanisms, amino acids biosynthesis, and expression of key genes relevant to salt stress defense.

plant biology↗

bioRxiv2022

Triose phosphate utilization stress during photosynthesis addressed with dynamic assimilation measurements

Oscillations in CO2 assimilation rate and associated fluorescence parameters have been observed alongside the triose phosphate utilization (TPU) limitation of photosynthesis for nearly 50 years. However, the mechanics of these oscillations are poorly understood. Here we utilize the recently developed Dynamic Assimilation Techniques (DAT) for measuring the rate of CO2 assimilation to increase our understanding of what physiological condition is required to cause oscillations. We found that TPU limiting conditions alone were insufficient, and that plants must enter TPU limitation quickly to cause oscillations. We found that ramps of CO2 caused oscillations proportional in strength to the speed of the ramp, and that ramps induce oscillations with worse outcomes than oscillations induced by step change of CO2 concentration. An initial overshoot is caused due to a temporary excess of available phosphate. During the overshoot, the plant out-performs steady state TPU and ribulose 1,5-bisphosphate regeneration limitations of photosynthesis but cannot exceed the rubisco limitation. We performed additional optical measurements which support the role of photosystem I reduction and oscillations in availability of NADP+ and ATP in supporting oscillations. HighlightRapid CO2 changes cause more oscillations of photosynthetic rate than a step change in CO2 or slowly changing CO2. Photosystem I acceptor side limitations may play a role.

plant biology↗

bioRxiv2022

Compartment-specific energy requirements of photosynthetic carbon metabolism in Camelina sativa leaves

Detailed knowledge about plant energy metabolism may aid crop improvements. Using published estimates of flux through central carbon metabolism, we phenotype energy metabolism in illuminated Camelina sativa leaves (grown at 22 {degrees}C, 500 mol photons m-2 s-1) and report several findings. First, the oxidative pentose phosphate pathway (OPPP) transfers 3.3% of the NADPH consumed in the Calvin-Benson cycle to the cytosol. NADPH supply proceeds at about 10% of the rate of net carbon assimilation. However, concomitantly respired CO2 accounts for 4.8% of total rubisco activity. Hence, 4.8% of the flux through the Calvin-Benson cycle and photorespiration is spent on supplying cytosolic NADPH, a significant investment. Associated energy requirements exceed the energy output of the OPPP. Thus, autotrophic carbon metabolism is not simply optimised for flux into carbon sinks but sacrifices carbon and energy use efficiency to support cytosolic energy metabolism. To reduce these costs, we suggest bioengineering plants with a repressed cytosolic OPPP, and an inserted cytosolic NADPH-dependent malate dehydrogenase tuned to compensate for the loss in OPPP activity (if required). Second, sucrose cycling is a minor investment in overall leaf energy metabolism but a significant investment in cytosolic energy metabolism. Third, leaf energy balancing strictly requires oxidative phosphorylation, cofactor export from chloroplasts, and peroxisomal NADH import. Fourth, mitochondria are energetically self-sufficient. Fifth, carbon metabolism has an ATP/NADPH demand ratio of 1.52 which is met if [≤]21.7% of whole electron flux is cyclic. Sixth, electron transport has a photon use efficiency of [≥]62%. Lastly, we discuss interactions between the OPPP and the cytosolic oxidation-reduction cycle in supplying leaf cytosolic NADPH. Main ConclusionThe oxidative pentose phosphate pathway provides cytosolic NADPH yet reduces carbon and energy use efficiency. Repressing this pathway and introducing cytosolic NADPH-dependent malate dehydrogenase may increase crop yields by {approx}5%.

plant biology↗

bioRxiv2021

Intramolecular 13C/12C signals inform about carbon allocation in plant leaves

Stable isotopes at natural abundance are key tools to study physiological processes occurring outside the temporal scope of manipulation and monitoring experiments. Whole-molecule carbon isotope ratios (13C/12C) enable assessments of plant carbon uptake yet conceal information about carbon allocation. Here, we identify an intramolecular 13C/12C signal at treering glucose C-5 and C-6 and develop experimentally testable theories on its origin. More specifically, we assess the potential of processes within C3 metabolism for signal introduction based (inter alia) on constraints on signal propagation posed by metabolic networks. We propose that the intramolecular signal reports carbon allocation into major metabolic pathways in actively photosynthesising leaf cells including the anaplerotic, shikimate, and non-mevalonate pathway. We support our theoretical framework by linking it to previously reported whole-molecule 13C/12C increases in cellulose of ozone-treated Betula pendula and a highly significant relationship between the intramolecular signal and tropospheric ozone concentration. Our theory postulates a pronounced preference of leaf-cytosolic triose-phosphate isomerase to catalyse the forward reaction in vivo (dihydroxyacetone phosphate to glyceraldehyde 3-phosphate). In conclusion, intramolecular 13C/12C analysis resolves information about carbon uptake and allocation enabling more comprehensive assessments of carbon metabolism than whole-molecule 13C/12C analysis. HighlightIntramolecular 13C/12C analysis resolves information about carbon uptake and allocation (and associated environmental controls) enabling more comprehensive assessments of carbon metabolism, plant-environment interactions, and environmental variability than whole-molecule 13C/12C analysis.

plant biology↗

bioRxiv2018

Supply and consumption of glucose 6-phosphate in the chloroplast stroma

Fructose 6-phosphate is an intermediate in the Calvin-Benson cycle and can be acted on by phosphoglucoisomerase to make glucose 6-phosphate (G6P) for starch synthesis. A high concentration of G6P is favorable for starch synthesis but can also stimulate G6P dehydrogenase initiating the glucose-6-phosphate shunt an alternative pathway around the Calvin-Benson cycle. A low concentration of glucose 6-phosphate will limit this futile cycle. In order to understand the biochemical regulation of plastidic glucose 6-phosphate supply and consumption, we characterized biochemical parameters of two key enzymes, phosphoglucoisomerase (PGI) and G6P dehydrogenase (G6PDH). We have found that the plastidic PGI in has a higher Km for G6P compared to that for fructose 6-phosphate. The Km of G6PDH isoform 1 is increased under reducing conditions. The other two isoforms exhibit less redox regulation; isoform 2 is the most inhibited by NADPH. Our results support the conclusion that PGI restricts stromal G6P synthesis limiting futile cycling via G6PDH. It also acts like a one-way valve, allowing carbon to leave the Calvin-Benson cycle but not reenter. We found flexible redox regulation of G6PDH that could regulate the glucose-6-phosphate shunt.\n\nHighlightGlucose 6-phosphate stimulates glucose-6-phosphate dehydrogenase. This enzyme is less active during the day but retains significant activity that is very sensitive to the concentration of glucose 6-phopshate.

biochemistry↗

bioRxiv2018

Triose phosphate utilization and beyond: from photosynthesis to end-product synthesis

During photosynthesis plants fix CO2 from the atmosphere onto ribulose-bisphosphate producing 3-phosphoglycerate, which is reduced to triose phosphates (TPs). The TPs are then converted into the end products of photosynthesis. When a plant is photosynthesizing very quickly it may not be possible to commit photosynthate to end product as fast as it is produced, causing a decrease in available phosphate and limiting the rate of photosynthesis to the rate of triose phosphate utilization (TPU). The occurrence of an observable TPU limitation is highly variable based on species and especially growth conditions, with TPU capacity seemingly regulated to be in just slight excess of the likely photosynthetic rate. The physiological effects of TPU limitation are discussed with an emphasis on interactions between the Calvin-Benson cycle and the light reactions. Methods for detecting TPU-limited data from gas exchange data are detailed, and the impact on modeling of some physiological effects are shown. Special consideration is given to common misconceptions about TPU.\n\nHighlightPhotosynthetic triose phosphate utilization limitation is discussed, highlighting misleading points in physiology and focusing on regulation.

plant biology↗

bioRxiv2018

Prospects for enhancing leaf photosynthetic capacity by manipulating mesophyll cell morphology

Leaves are beautifully specialized organs designed to maximize the use of light and CO2 for photosynthesis. Engineering leaf anatomy therefore brings great potential to enhance photosynthetic capacity. Here we review the effect of the dominant leaf anatomical traits on leaf photosynthesis and confirm that a high chloroplast surface area exposed to intercellular airspace per unit leaf area (Sc) is critical for efficient photosynthesis. The possibility of improving Sc through appropriately increasing mesophyll cell density is further analyzed. The potential influences of modifying mesophyll cell morphology on CO2 diffusion, light distribution within the leaf, and other physiological processes are also discussed. Some potential target genes regulating leaf mesophyll cell proliferation and expansion are explored. Indeed, more comprehensive research is needed to understand how manipulating mesophyll cell morphology through editing the potential target genes impact leaf photosynthetic capacity and related physiological processes. This will pinpoint the targets for engineering leaf anatomy to maximize photosynthetic capacity.\n\nHighlightCell morphology in leaves affects photosynthesis by controlling CO2 diffusion and light distribution. Recent work has uncovered genes that control cell size, shape, and number paving the way improved photosynthesis.

plant biology↗

bioRxiv2018

Loss of Peroxisomal Hydroxypyruvate Reductase Inhibits Triose Phosphate Isomerase but Stimulates Cyclic Photosynthetic Electron Flow and the Glc-6P-Phosphate Shunt

The oxygenation of ribulose 1,5-bisphosphate by Rubisco is the first step in photorespiration and reduces the efficiency of photosynthesis in C3 plants. Our recent data indicates that mutants in photorespiration have increased rates of photosynthetic cyclic electron flow around photosystem I. We investigated mutant lines lacking peroxisomal hydroxypyruvate reductase to determine if there are connections between 2-PG accumulation and cyclic electron flow. We found that 2-PG is a competitive inhibitor of triose phosphate isomerase (TPI), an enzyme in the Calvin-Benson cycle that converts glyceraldehyde 3-phosphate to dihydroxyacetone phosphate. This block in metabolism could be overcome if glyceraldehyde 3-phosphate is exported to the cytosol where the cytosolic triose phosphate isomerase could convert it to dihydroxyacetone phosphate. We found evidence that carbon is reimported as Glc-6P-phosphate forming a cytosolic bypass around the block of stromal TPI. However, this also stimulates a Glc-6P-phosphate shunt, which consumes ATP, which can be compensated by higher rates of cyclic electron flow.\n\nOnce Sentence SummaryTriose phosphate isomerase is inhibited in plants lacking hydroxypyruvate reductase 1 and this is overcome by exporting triose phosphate to the cytosol and importing Glc-6P, which stimulates a Glc-6P-phosphate shunt and cyclic electron flow.

plant biology↗