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This review explores current understanding in crop photosynthesis and temperature across scales, linking enzyme processes within the leaf to stomata, plant transport systems, individual plants, and ecosystem-scale responses., 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.

Species have different strategies for loading sugars into the phloem, which vary in the route that sugars take to enter the phloem and the energetics of sugar accumulation. Species with passive phloem loading are hypothesized to have less flexibility in response to changes in some environmental conditions because sucrose export from mesophyll cells is dependent on fixed anatomical plasmodesmatal connections. Passive phloem loaders also have high mesophyll sugar content, and may be less likely to exhibit sugar-mediated down-regulation of photosynthetic capacity at elevated CO2 concentrations. To date, the effect of phloem loading strategy on the response of plant carbon metabolism to rising atmospheric CO2 concentrations is unclear, despite the widespread impacts of rising CO2 on plants. Over three field seasons, five species with apoplastic loading, passive loading, or polymer-trapping were grown at ambient and elevated CO2 concentration in free air concentration enrichment plots. Light-saturated rate of photosynthesis, photosynthetic capacity, leaf carbohydrate content, and anatomy were measured and compared among the species. All five species showed significant stimulation in midday photosynthetic CO2 uptake by elevated CO2 even though the two passive loading species showed significant down-regulation of maximum Rubisco carboxylation capacity at elevated CO2. There was a trend toward greater starch accumulation at elevated CO2 in all species, and was most pronounced in passive loaders. From this study, we cannot conclude that phloem loading strategy is a key determinant of plant response to elevated CO2, but compelling differences in response counter to our hypothesis were observed. A phylogenetically controlled experiment with more species may be needed to fully test the hypothesis.

Increasing atmospheric carbon dioxide concentration ([CO2]) directly stimulates photosynthesis and reduces stomatal conductance in C3 plants. Both of these physiological effects have the potential to alter phloem function at elevated [CO2]. Recent research has clearly established that photosynthetic capacity is correlated to vascular traits associated with phloem loading and water transport, but the effects of elevated [CO2] on these relationships are largely unexplored. Plants also employ different strategies for loading sucrose and other sugars into the phloem, and there is potential for species with different phloem loading strategies to respond differently to elevated [CO2]. Recent research manipulating sucrose transporters and other key enzymes with roles in phloem loading show promise for maximizing crop performance in an elevated [CO2] world.

Increasing atmospheric carbon dioxide concentration ([CO

International audience; Botrytis cinerea is the causing agent of the grey mold disease in more than 200 crop species. While signaling pathways leading to the basal resistance against this fungus are well described, the role of the import of sugars into host cells remains to be investigated. In Arabidopsis thaliana, apoplastic hexose retrieval is mediated by the activity of sugar transport proteins (STPs). Expression analysis of the 14 STP genes revealed that only STP13 was induced in leaves challenged with B. cinerea. STP13-modified plants were produced and assayed for their resistance to B. cinerea and glucose transport activity. We report that STP13-deficient plants exhibited an enhanced susceptibility and a reduced rate of glucose uptake. Conversely, plants with a high constitutive level of STP13 protein displayed an improved capacity to absorb glucose and an enhanced resistance phenotype. The correlation between STP13 transcripts, protein accumulation, glucose uptake rate and resistance level indicates that STP13 contributes to the basal resistance to B. cinerea by limiting symptom development and points out the importance of the host intracellular sugar uptake in this process. We postulate that STP13 would participate in the active resorption of hexoses to support the increased energy demand to trigger plant defense reactions and to deprive the fungus by changing sugar fluxes toward host cells.

International audience; Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses...) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.