Arterial blood gas measurements are different for brachycephalic and nonbrachycephalic dogs acclimatized to an altitude of 1,535 meters.

OBJECTIVE: To define reference intervals (RIs) for arterial blood gas (aBG) measurements in healthy, nonsedated, dolichocephalic, and mesocephalic (nonbrachycephalic) dogs at approximately 1,535 m above sea level and compare these findings with healthy, nonsedated, brachycephalic dogs living at the same altitude. ANIMALS: 120 adult nonbrachycephalic dogs and 20 adult brachycephalic dogs. METHODS: Cases were prospectively enrolled from October 2021 to June 2022. Dogs were enrolled from the community or after presentation for wellness examinations or minor injuries including lacerations, nail injuries, and lameness. Physical examinations and systolic blood pressure (sBP) measurements were obtained before blood sample collection. Arterial blood was collected from the dorsal pedal artery or femoral artery. After data collection, brachycephalic dogs underwent pre- and postexercise tolerance assessments. RESULTS: The mean and RI values for arterial pH (7.442; 7.375 to 7.515), partial pressure of oxygen in arterial blood (Pao2; 78.3; 59.2 to 92.7 mm Hg), partial pressure of carbon dioxide in arterial blood (Paco2; 28.0; 21.5 to 34.4 mm Hg), saturation of arterial oxygen (Sao2; 98.4; 84.3% to 101.4%), HCO3 (18.9; 14.9 to 22.4 mmol/L), concentration of total hemoglobin (ctHb; 17.5; 13.4 to 21.1 g/dL), and sBP (133; 94 to 180 mm Hg) were established for healthy nonbrachycephalic dogs at 1,535-m altitude. All aBG measurements were statistically and clinically different from those previously reported for dogs at sea level. Brachycephalic dogs had significantly lower Pao2 and Sao2 (P = .0150 and P = .0237, respectively) and significantly higher ctHb (P = .0396) compared to nonbrachycephalic dogs acclimatized to the same altitude; the nonbrachycephalic RIs were not transferable to the brachycephalic dogs for Pao2. CLINICAL RELEVANCE: This study represents the first collation of aBG measurements for healthy nonbrachycephalic dogs acclimatized to an altitude of 1,535 m. Additionally, this study identified differences in arterial oxygenation measurements between brachycephalic and nonbrachycephalic dogs. RIs in brachycephalic dogs need to be established.

Surgical interventions and outcome in a population of canine trauma patients.

OBJECTIVE: To determine signalment, injury type, trauma severity score, and outcome of canine trauma patients undergoing surgical (emergency room [ER] or operating room [OR]) and nonsurgical treatment in addition to time to surgery, specialty services involved, and cost in the OR surgery population. DESIGN: Retrospective evaluation of medical record and hospital trauma registry data on canine trauma cases. SETTING: University teaching hospital. ANIMALS: One thousand six hundred and thirty dogs presenting for traumatic injury between May 2017 and July 2020. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Demographics and outcome were compared for canine trauma patients undergoing OR surgery (12.8%, 208/1630), ER surgery (39.1%, 637/1630), or no surgical intervention (48.2%, 785/1630). Among the 2 surgical groups, 98.9% (836/845) survived to discharge compared with 92.2% (724/785) of the nonsurgical group (P < 0.0001). The OR surgical group had significantly higher median Animal Trauma Triage scores (2 vs 1, P < 0.0001) and median days in hospital (2 vs < 1, P < 0.0001) compared with the other groups. For the OR surgical cohort, electronic medical records were reviewed to determine the specialty surgery service involved, time to and duration of anesthesia and surgery, and visit cost. The most common surgery services involved were orthopedics (45.2%, 94/208) and general surgery (26.9%, 56/208). Neurology and general surgery cases required the longest median length of stay in hospital, and ophthalmology and dentistry cases required the shortest. The median cost of visit was highest in neurology ($10,032) and lowest in ophthalmology ($2305) and dentistry ($2404). CONCLUSIONS: Surgical intervention in canine trauma patients appears to be associated with higher survival rates, and among the surgery groups, mortality was highest in the ER and general surgery groups. OR surgical intervention, in particular general surgery and neurology, was associated with increased length of hospitalization, increased cost, and higher Animal Trauma Triage scores.

A guide to photosynthetic gas exchange measurements: Fundamental principles, best practice and potential pitfalls.

Gas exchange measurements enable mechanistic insights into the processes that underpin carbon and water fluxes in plant leaves which in turn inform understanding of related processes at a range of scales from individual cells to entire ecosytems. Given the importance of photosynthesis for the global climate discussion it is important to (a) foster a basic understanding of the fundamental principles underpinning the experimental methods used by the broad community, and (b) ensure best practice and correct data interpretation within the research community. In this review, we outline the biochemical and biophysical parameters of photosynthesis that can be investigated with gas exchange measurements and we provide step-by-step guidance on how to reliably measure them. We advise on best practices for using gas exchange equipment and highlight potential pitfalls in experimental design and data interpretation. The Supporting Information contains exemplary data sets, experimental protocols and data-modelling routines. This review is a community effort to equip both the experimental researcher and the data modeller with a solid understanding of the theoretical basis of gas-exchange measurements, the rationale behind different experimental protocols and the approaches to data interpretation.

Sidestream dark field imaging and biomarker evaluation reveal minimal significant changes to the microcirculation and glycocalyx in a canine hemorrhagic shock model.

OBJECTIVE: To investigate the effects of hemorrhagic shock and fresh whole blood resuscitation on the microcirculation and endothelial glycocalyx using sidestream dark field (SDF) imaging and plasma biomarkers. ANIMALS: 8 purpose-bred dogs. METHODS: Pressure-targeted hemorrhagic shock was induced in anesthetized dogs. SDF measurement of perfused boundary region and microcirculatory variables (RBC flow, total vessel density, and relative and absolute capillary blood volume), biomarker measurement (heparan sulfate, hyaluronan, VE-cadherin, and syndecan-1), mean arterial blood pressure, and cardiac output measurement were performed before anesthesia (TP0), after induction (TP1), after hemorrhagic shock (TP2), and after 50% retransfusion (TP3) and 100% retransfusion (TP4). RESULTS: At TP1, TP2, TP3, and TP4, mean arterial blood pressure was 74.25 ± 7.17 mm Hg, 49.50 ± 13.74 mm Hg, 63.50 ± 13.29 mm Hg, and 71.38 ± 8.77 mm Hg, and cardiac output was 2.57 ± 1.01 L/min, 0.8 ± 0.36 L/min, 1.81 ± 0.57 L/min, and 2.93 ± 1.22 L/min, respectively. Heparan sulfate, hyaluronan, syndecan-1, and VE-cadherin ranges were 24.80 to 77.72 ng/mL, 5.77 to 105.06 ng/mL, below detection to 1,545.69 pg/mL, and 0 to 2.52 ng/mL, respectively. Perfused boundary region, RBC flow, total vessel density, and relative and absolute capillary blood volume ranges were 1.75 to 2.68 µm, 89.6 to 584.5 µm/s, 51.7 to 1,914.3 mm/m2, 0.94 to 1.53 103 µm3, and 1.50 to 94.30 103 µm3, respectively. Heparan sulfate decreased significantly over time (P = .016). No significant differences were found for microcirculatory variables, perfused boundary regions, or other biomarkers. CLINICAL RELEVANCE: This was the first study to assess microvascular dysfunction and endothelial shedding in a canine hemorrhagic shock model using SDF microscopy (Glycocheck) and plasma biomarkers. Further studies are needed to determine clinical relevance.

Transgenic strategies to improve the thermotolerance of photosynthesis.

Warming driven by the accumulation of greenhouse gases in the atmosphere is irreversible over at least the next century, unless practical technologies are rapidly developed and deployed at scale to remove and sequester carbon dioxide from the atmosphere. Accepting this reality highlights the central importance for crop agriculture to develop adaptation strategies for a warmer future. While nearly all processes in plants are impacted by above optimum temperatures, the impact of heat stress on photosynthetic processes stand out for their centrality. Here, we review transgenic strategies that show promise in improving the high-temperature tolerance of specific subprocesses of photosynthesis and in some cases have already been shown in proof of concept in field experiments to protect yield from high temperature-induced losses. We also highlight other manipulations to photosynthetic processes for which full proof of concept is still lacking but we contend warrant further attention. Warming that has already occurred over the past several decades has had detrimental impacts on crop production in many parts of the world. Declining productivity presages a rapidly developing global crisis in food security particularly in low income countries. Transgenic manipulation of photosynthesis to engineer greater high-temperature resilience holds encouraging promise to help meet this challenge.

Surgical interventions and outcome in a population of feline trauma patients.

OBJECTIVE: To determine signalment, injury type, trauma severity score, and outcome of feline trauma patients undergoing surgical (emergency room [ER] and operating room [OR]) and nonsurgical treatments in addition to time to surgery, specialty services involved, and cost in the OR surgery population. DESIGN: Retrospective evaluation of medical record and hospital trauma registry data on feline trauma cases. SETTING: University teaching hospital. ANIMALS: Two hundred and fifty-one cats presenting for traumatic injury between May 2017 and July 2020. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: Demographics and outcomes were compared for cats undergoing surgical intervention in an OR (12%, 31/251) or an ER (23%, 58/251) setting and feline trauma patients without surgical intervention (65%, 162/251). Between the 2 surgical groups, 99% survived to discharge compared to 73.5% of the nonsurgical group (P < 0.0001). For the OR surgical cohort, electronic medical records were reviewed to determine the specialty surgery service involved, time to and duration of anesthesia and surgery, and visit cost. The most common surgery services involved were orthopedics (41%, 12/29) and dentistry (38%, 11/29), and the most common surgeries performed were mandibular fracture stabilization (8/29) and internal fixation for long bone fractures (8/29). The ER surgical group had a significantly lower Animal Trauma Triage score than the OR group (P < 0.0001), but a significant difference was not found between OR surgical and nonsurgical groups (P = 0.0553). No difference in modified Glasgow Coma Scale score was found between any groups. CONCLUSIONS: Surgical intervention in feline trauma patients appears to be associated with higher survival rates, but no difference in mortality was found across surgery services. OR surgical intervention, in particular, orthopedic surgery, was associated with increased length of hospitalization, increased cost, and increased use of blood products.

Temperature-induced changes in Arabidopsis Rubisco activity and isoform expression.

In many plant species, expression of the nuclear encoded Rubisco small subunit (SSu) varies with environmental changes, but the functional role of any changes in expression remains unclear. In this study, we investigated the impact of differential expression of Rubisco SSu isoforms on carbon assimilation in Arabidopsis. Using plants grown at contrasting temperatures (10 °C and 30 °C), we confirm the previously reported temperature response of the four RbcS genes and extend this to protein expression, finding that warm-grown plants produce Rubisco containing ~65% SSu-B and cold-grown plants produce Rubisco with ~65% SSu-A as a proportion of the total pool of subunits. We find that these changes in isoform concentration are associated with kinetic changes to Rubisco in vitro: warm-grown plants produce a Rubisco having greater CO2 affinity (i.e. higher SC/O and lower KC) but lower kcatCO2 at warm measurement temperatures. Although warm-grown plants produce 38% less Rubisco than cold-grown plants on a leaf area basis, warm-grown plants can maintain similar rates of photosynthesis to cold-grown plants at ambient CO2 and 30 °C, indicating that the carboxylation capacity of warm-grown Rubisco is enhanced at warmer measurement temperatures, and is able to compensate for the lower Rubisco content in warm-grown plants. This association between SSu isoform expression and maintenance of Rubisco activity at high temperature suggests that SSu isoform expression could impact the temperature response of C3 photosynthesis.

Removal of redox-sensitive Rubisco Activase does not alter Rubisco regulation in soybean.

Rubisco activase (Rca) facilitates the catalytic repair of Rubisco, the CO2-fixing enzyme of photosynthesis, following periods of darkness, low to high light transitions or stress. Removal of the redox-regulated isoform of Rubisco activase, Rca-α, enhances photosynthetic induction in Arabidopsis and has been suggested as a strategy for the improvement of crops, which may experience frequent light transitions in the field; however, this has never been tested in a crop species. Therefore, we used RNAi to reduce the Rca-α content of soybean (Glycine max cv. Williams 82) below detectable levels and then characterized the growth, photosynthesis, and Rubisco activity of the resulting transgenics, in both growth chamber and field conditions. Under a 16 h sine wave photoperiod, the reduction of Rca-α contents had no impact on morphological characteristics, leaf expansion rate, or total biomass. Photosynthetic induction rates were unaltered in both chamber-grown and field-grown plants. Plants with reduced Rca-α content maintained the ability to regulate Rubisco activity in low light just as in control plants. This result suggests that in soybean, Rca-α is not as centrally involved in the regulation of Rca oligomer activity as it is in Arabidopsis. The isoform stoichiometry supports this conclusion, as Rca-α comprises only ~ 10% of the Rubisco activase content of soybean, compared to ~ 50% in Arabidopsis. This is likely to hold true in other species that contain a low ratio of Rca-α to Rca-ß isoforms.

Acidic chemical corneal ulceration secondary to nail polish spill in a puppy.

PURPOSE: To describe the treatment of an acidic chemical corneal ulceration in a puppy secondary to nail polish spilling on and adhering to the cornea. CASE SUMMARY: A 12-week-old neutered male Australian Shepherd mix dog was presented to Colorado State University Veterinary Teaching Hospital's (CSU-VTH) Emergency and Urgent Care service acutely after exposure to nail polish spilling on the left eye (OS). Initial ophthalmic examination revealed nail polish adhered to approximately 80% of the cornea with moderate diffuse corneal edema and chemosis, and green nail polish adhered to the skin and fur of the periocular area. Copious flushing with eye wash was performed, but no areas of reduced nail polish adherence were noted. The patient was treated with 1 drop of topical ofloxacin 0.3% ophthalmic solution OS and hospitalized overnight, receiving hyaluronic acid ophthalmic lubrication every hour OS. The treatment plan was carried out for 6 h until time of transfer. In the morning, CSU-VTH's Ophthalmology service removed a nonadhered nail polish plaque in 1 piece using Bishop-Harmon tissue forceps. Following removal, a superficial ulcer secondary to an acidic chemical burn covering 100% of the corneal surface was noted, as well as moderate diffuse corneal edema. Following topical treatment for 8 days, the superficial ulcer healed completely, with no significant long-term consequences. UNIQUE INFORMATION PROVIDED: This is the first report of management of an acidic chemical corneal ulceration secondary to nail polish spill in a puppy. Early assessment and vigilance in treatment was essential for a good prognosis and outcome.

Alternative pathway to photorespiration protects growth and productivity at elevated temperatures in a model crop.

Adapting crops to warmer growing season temperatures is a major challenge in mitigating the impacts of climate change on crop production. Warming temperatures drive greater evaporative demand and can directly interfere with both reproductive and vegetative physiological processes. Most of the world's crop species have C3 photosynthetic metabolism for which increasing temperature means higher rates of photorespiration, wherein the enzyme responsible for fixing CO2 fixes O2 instead followed by an energetically costly recycling pathway that spans several cell compartments. In C3 crops like wheat, rice and soybean, photorespiration translates into large yield losses that are predicted to increase as global temperature warms. Engineering less energy-intensive alternative photorespiratory pathways into crop chloroplasts drives increases in C3 biomass production under agricultural field conditions, but the efficacy of these pathways in mitigating the impact of warmer growing temperatures has not been tested. We grew tobacco plants expressing an alternative photorespiratory pathway under current and elevated temperatures (+5 °C) in agricultural field conditions. Engineered plants exhibited higher photosynthetic quantum efficiency under heated conditions than the control plants, and produced 26% (between 16% and 37%) more total biomass than WT plants under heated conditions, compared to 11% (between 5% and 17%) under ambient conditions. That is, engineered plants sustained 19% (between 11% and 21%) less yield loss under heated conditions compared to non-engineered plants. These results support the theoretical predictions of temperature impacts on photorespiratory losses and provide insight toward the optimisation strategies required to help sustain or improve C3 crop yields in a warming climate.

Genome-wide analysis and transcriptional regulation of the typical and atypical thioredoxins in Arabidopsis thaliana.

Thioredoxins (TRXs), a large subclass of ubiquitous oxidoreductases, are involved in thiol redox regulation. Here, we performed a comprehensive analysis of TRXs in the Arabidopsis thaliana genome, revealing 41 genes encoding 18 typical and 23 atypical TRXs, and 6 genes encoding thioredoxin reductases (TRs). The high number of atypical TRXs indicates special functions in plants that mostly await elucidation. We identified an atypical class of thioredoxins called TRX-c in the genomes of photosynthetic eukaryotes. Localized to the chloroplast, TRX-c displays atypical CPLC, CHLC and CNLC motifs in the active sites. In silico analysis of the transcriptional regulations of TRXs revealed high expression of TRX-c in leaves and strong regulation under cold, osmotic, salinity and metal ion stresses.

The effect of increasing temperature on crop photosynthesis: from enzymes to ecosystems.

As global land surface temperature continues to rise and heatwave events increase in frequency, duration, and/or intensity, our key food and fuel cropping systems will likely face increased heat-related stress. A large volume of literature exists on exploring measured and modelled impacts of rising temperature on crop photosynthesis, from enzymatic responses within the leaf up to larger ecosystem-scale responses that reflect seasonal and interannual crop responses to heat. This review discusses (i) how crop photosynthesis changes with temperature at the enzymatic scale within the leaf; (ii) how stomata and plant transport systems are affected by temperature; (iii) what features make a plant susceptible or tolerant to elevated temperature and heat stress; and (iv) how these temperature and heat effects compound at the ecosystem scale to affect crop yields. Throughout the review, we identify current advancements and future research trajectories that are needed to make our cropping systems more resilient to rising temperature and heat stress, which are both projected to occur due to current global fossil fuel emissions.

Ozone tolerant maize hybrids maintain Rubisco content and activity during long-term exposure in the field.

Ozone pollution is a damaging air pollutant that reduces maize yields equivalently to nutrient deficiency, heat, and aridity stress. Therefore, understanding the physiological and biochemical responses of maize to ozone pollution and identifying traits predictive of ozone tolerance is important. In this study, we examined the physiological, biochemical and yield responses of six maize hybrids to elevated ozone in the field using Free Air Ozone Enrichment. Elevated ozone stress reduced photosynthetic capacity, in vivo and in vitro, decreasing Rubisco content, but not activation state. Contrary to our hypotheses, variation in maize hybrid responses to ozone was not associated with stomatal limitation or antioxidant pools in maize. Rather, tolerance to ozone stress in the hybrid B73 × Mo17 was correlated with maintenance of leaf N content. Sensitive lines showed greater ozone-induced senescence and loss of photosynthetic capacity compared to the tolerant line.

Successful management of acute bilirubin encephalopathy in a dog with immune-mediated hemolytic anemia using therapeutic plasma exchange.

OBJECTIVE: To describe the successful management of acute bilirubin encephalopathy in a dog with immune-mediated hemolytic anemia (IMHA) treated with therapeutic plasma exchange (TPE) in conjunction with conventional medical management. CASE SUMMARY: A 6-year-old neutered male Australian Cattle Dog diagnosed with IMHA developed severe hyperbilirubinemia and stupor within the first 48 hours of implementing immunosuppressive therapy consisting of corticosteroids and mycophenolate. The patient received 4 blood transfusions during this period, but remained severely anemic PCV (18%) and experienced a subsequent increase in total bilirubin from 78 µmol/L (4.6 mg/dL) to a peak value of 1,563 µmol/L (91.4 mg/dL). The patient's neurological status rapidly deteriorated, resulting in lateral recumbency, vertical nystagmus, extensor rigidity, and stuporous mentation. Over the next 3 days, TPE was provided once every 24 hours, decreasing serum bilirubin, immunoglobulin G (IgG), and immunoglobulin M (IgM). The patient's red blood cell (RBC) transfusion requirements decreased immediately, requiring only 1 transfusion over the next 7 days that was required due to procedure-associated blood loss. Gradual neurological improvement was noted as serum bilirubin decreased. A brain magnetic resonance imaging (MRI) did not reveal any structural abnormalities and the patient was discharged after 11 days of hospitalization. Following discharge, the patient had complete remission of IMHA without any residual neurological deficits. Therapeutic plasma exchange played an integral role in case management and was successful in reducing bilirubin, IgG, and IgM. NEW OR UNIQUE INFORMATION PROVIDED: Bilirubin encephalopathy has been rarely reported in small animal medicine and cases have been limited to postmortem documentation. This is the first suspected case of acute bilirubin encephalopathy in a dog that survived and describes the clinical course of disease. The kinetics of serum bilirubin, IgG, and IgM concentrations before and after TPE and throughout the hospitalization period are also described.

In vivo evidence for a regulatory role of phosphorylation of Arabidopsis Rubisco activase at the Thr78 site.

Arabidopsis Rubisco activase (Rca) is phosphorylated at threonine-78 (Thr78) in low light and in the dark, suggesting a potential regulatory role in photosynthesis, but this has not been directly tested. To do so, we transformed an rca-knockdown mutant largely lacking redox regulation with wild-type Rca-ß or Rca-ß with Thr78-to-Ala (T78A) or Thr78-to-Ser (T78S) site-directed mutations. Interestingly, the T78S mutant was hyperphosphorylated at the Ser78 site relative to Thr78 of the Rca-ß wild-type control, as evidenced by immunoblotting with custom antibodies and quantitative mass spectrometry. Moreover, plants expressing the T78S mutation had reduced photosynthesis and quantum efficiency of photosystem II (ϕPSII) and reduced growth relative to control plants expressing wild-type Rca-ß under all conditions tested. Gene expression was also altered in a manner consistent with reduced growth. In contrast, plants expressing Rca-ß with the phospho-null T78A mutation had faster photosynthetic induction kinetics and increased ϕPSII relative to Rca-ß controls. While expression of the wild-type Rca-ß or the T78A mutant fully rescued the slow-growth phenotype of the rca-knockdown mutant grown in a square-wave light regime, the T78A mutants grew faster than the Rca-ß control plants at low light (30 µmol photons m-2 s-1) and in a fluctuating low-light/high-light environment. Collectively, these results suggest that phosphorylation of Thr78 (or Ser78 in the T78S mutant) plays a negative regulatory role in vivo and provides an explanation for the absence of Ser at position 78 in terrestrial plant species.

Synthetic glycolate metabolism pathways stimulate crop growth and productivity in the field.

Photorespiration is required in C3 plants to metabolize toxic glycolate formed when ribulose-1,5-bisphosphate carboxylase-oxygenase oxygenates rather than carboxylates ribulose-1,5-bisphosphate. Depending on growing temperatures, photorespiration can reduce yields by 20 to 50% in C3 crops. Inspired by earlier work, we installed into tobacco chloroplasts synthetic glycolate metabolic pathways that are thought to be more efficient than the native pathway. Flux through the synthetic pathways was maximized by inhibiting glycolate export from the chloroplast. The synthetic pathways tested improved photosynthetic quantum yield by 20%. Numerous homozygous transgenic lines increased biomass productivity by >40% in replicated field trials. These results show that engineering alternative glycolate metabolic pathways into crop chloroplasts while inhibiting glycolate export into the native pathway can drive increases in C3 crop yield under agricultural field conditions.

Temperature response of Rubisco kinetics in Arabidopsis thaliana: thermal breakpoints and implications for reaction mechanisms.

Enhancement of Rubisco kinetics could improve photosynthetic efficiency, ultimately resulting in increased crop yield. However, imprecise knowledge of the reaction mechanism and the individual rate constants limits our ability to optimize the enzyme. Membrane inlet mass spectrometry (MIMS) may offer benefits over traditional methods for determining individual rate constants of the Rubisco reaction mechanism, as it can directly monitor concentration changes in CO2, O2, and their isotopologs during assays. However, a direct comparison of MIMS with the traditional radiolabel method of determining Rubisco kinetic parameters has not been made. Here, the temperature responses of Rubisco kinetic parameters from Arabidopsis thaliana were measured using radiolabel and MIMS methods. The two methods provided comparable parameters above 25 °C, but temperature responses deviated at low temperature as MIMS-derived catalytic rates of carboxylation, oxygenation, and CO2/O2 specificity showed thermal breakpoints. Here, we discuss the variability and uncertainty surrounding breakpoints in the Rubisco temperature response and the relevance of individual rate constants of the reaction mechanisms to potential breakpoints.

Optimizing photorespiration for improved crop productivity.

In C3 plants, photorespiration is an energy-expensive process, including the oxygenation of ribulose-1,5-bisphosphate (RuBP) by ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and the ensuing multi-organellar photorespiratory pathway required to recycle the toxic byproducts and recapture a portion of the fixed carbon. Photorespiration significantly impacts crop productivity through reducing yields in C3 crops by as much as 50% under severe conditions. Thus, reducing the flux through, or improving the efficiency of photorespiration has the potential of large improvements in C3 crop productivity. Here, we review an array of approaches intended to engineer photorespiration in a range of plant systems with the goal of increasing crop productivity. Approaches include optimizing flux through the native photorespiratory pathway, installing non-native alternative photorespiratory pathways, and lowering or even eliminating Rubisco-catalyzed oxygenation of RuBP to reduce substrate entrance into the photorespiratory cycle. Some proposed designs have been successful at the proof of concept level. A plant systems-engineering approach, based on new opportunities available from synthetic biology to implement in silico designs, holds promise for further progress toward delivering more productive crops to farmer's fields.