Growth, reproductive phenology and yield responses of a potential biofuel plant, Jatropha curcas grown under projected 2050 levels of elevated CO2

Amelioration of plant responses to drought under elevated CO2 by rejuvenating photosynthesis and nitrogen use efficiency: implications for future climate-resilient crops

The contemporary global agriculture is beset with serious threats from diverse eco-environmental conditions causing decreases in crop yields by ~ 15%. These yield losses might increase further due to climate change scenarios leading to increased food prices triggering social unrest and famines. Urbanization and industrialization are often associated with rapid increases in greenhouse gases (GHGs) especially atmospheric CO₂ concentration [(CO₂)]. Increase in atmospheric [CO₂] significantly improved crop photosynthesis and productivity initially which vary with plant species, genotype, [CO₂] exposure time and biotic as well as abiotic stress factors. Numerous attempts have been made using different plant species to unravel the physiological, cellular and molecular effects of elevated [CO₂] as well as drought. This review focuses on plant responses to elevated [CO₂] and drought individually as well as in combination with special reference to physiology of photosynthesis including its acclimation. Furthermore, the functional role of nitrogen use efficiency (NUE) and its relation to photosynthetic acclimation and crop productivity under elevated [CO₂] and drought are reviewed. In addition, we also discussed different strategies to ameliorate the limitations of ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration. Further, improved stomatal and mesophyll conductance and NUE for enhanced crop productivity under fast changing global climate conditions through biotechnological approaches are also discussed here. We conclude that multiple gene editing approaches for key events in photosynthetic processes would serve as the best strategy to generate resilient crop plants with improved productivity under fast changing climate.

Temporal variability in tree responses to elevated atmospheric CO2

At leaf level, elevated atmospheric CO₂ concentration (eCO₂ ) results in stimulation of carbon net assimilation and reduction of stomatal conductance. However, a comprehensive understanding of the impact of eCO₂ at larger temporal (seasonal and annual) and spatial (from leaf to whole-tree) scales is still lacking. Here, we review overall trends, magnitude and drivers of dynamic tree responses to eCO₂ , including carbon and water relations at the leaf and the whole-tree level. Spring and early season leaf responses are most susceptible to eCO₂ and are followed by a down-regulation towards the onset of autumn. At the whole-tree level, CO₂ fertilization causes consistent biomass increments in young seedlings only, whereas mature trees show a variable response. Elevated CO₂ -induced reductions in leaf stomatal conductance do not systematically translate into limitation of whole-tree transpiration due to the unpredictable response of canopy area. Reduction in the end-of-season carbon sink demand and water-limiting strategies are considered the main drivers of seasonal tree responses to eCO₂ . These large temporal and spatial variabilities in tree responses to eCO₂ highlight the risk of predicting tree behavior to eCO₂ based on single leaf-level point measurements as they only reveal snapshots of the dynamic responses to eCO₂ .

Honoring eight senior distinguished plant biologists from India

We summarize here research contributions of eight stalwarts in photosynthesis research from India. These distinguished scientists (Shree Kumar Apte, Basanti Biswal, Udaya C. Biswal, Agepati S. Raghavendra, Attipalli Ramachandra Reddy, Prafullachandra Vishnu (Raj) Sane, Baishnab Charan Tripathy, and Dinesh C. Uprety) were honored on November 2, 2017, at the School of Life Sciences, University of Hyderabad. We include here two group photographs of this special event, which was organized by the Department of Plant Sciences, during the 8th International Conference on Photosynthesis and Hydrogen Energy Research for Sustainability-2017 ( https://prs.science/wp-content/uploads/2017/10/Photosynthesis-Research-for-Sustainability-2017.pdf , also available at: http://www.life.illinois.edu/govindjee/world-historical.html ). The main conference had honored three international scientists: William Cramer (Purdue University. West Lafayette, Indiana, USA), Govindjee (University of Illinois at Urbana-Champaign, Illinois, USA, one of the authors here); and Agepati S. Raghavendra (University of Hyderabad, India, one of those honored here as well); see papers in this Special Issue, edited by Suleyman Allakhverdiev, one of the authors here.

Stomatal Conductance and Morphology of Arbuscular Mycorrhizal Wheat Plants Response to Elevated CO2 and NaCl Stress

Stomata play a critical role in the regulation of gas exchange between the interior of the leaf and the exterior environment and are affected by environmental and endogenous stimuli. This study aimed to evaluate the effect of the arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis, on the stomatal behavior of wheat (Triticum aestivum L.) plants under combination with elevated CO₂ and NaCl stress. Wheat seedlings were exposed to ambient (400 ppm) or elevated (700 ppm) CO₂ concentrations and 0, 1, and 2 g kg^-1 dry soil NaCl treatments for 10 weeks. AM symbiosis increased the leaf area and stomatal density (SD) of the abaxial surface. Stomatal size and the aperture of adaxial and abaxial leaf surfaces were higher in the AM than non-AM plants under elevated CO₂ and salinity stress. AM plants showed higher stomatal conductance (g _s ) and maximum rate of g _s to water vapor (g _smax ) compared with non-AM plants. Moreover, leaf water potential (Ψ) was increased and carbon isotope discrimination (Δ¹³C) was decreased by AM colonization, and both were significantly associated with stomatal conductance. The results suggest that AM symbiosis alters stomatal morphology by changing SD and the size of the guard cells and stomatal pores, thereby improving the stomatal conductance and water relations of wheat leaves under combined elevated CO₂ and salinity stress.

Molecular insights into photosynthesis and carbohydrate metabolism in Jatropha curcas grown under elevated CO2 using transcriptome sequencing and assembly

Jatropha curcas L. (Family - Euphorbiaceae) is a perennial tree of special interest due to its potential as a biofuel plant with high carbon sequestration. In this study, physiological investigations coupled with transcriptomics in relation to photosynthesis were evaluated in Jatropha grown under ambient (395 ppm) and elevated (550 ppm) CO2 atmosphere. Morphophysiological analysis revealed that Jatropha sustained enhanced photosynthesis during its growth under elevated CO2 for one year which might be linked to improved CO2 assimilation physiology and enhanced sink activity. We sequenced and analyzed the leaf transcriptome of Jatropha after one year of growth in both conditions using Illumina HiSeq platform. After optimized assembly, a total of 69,581 unigenes were generated. The differential gene expression (DGE) analysis revealed 3013 transcripts differentially regulated in elevated CO2 conditions. The photosynthesis regulatory genes were analysed for temporal expression patterns at four different growth phases which highlighted probable events contributing to enhanced growth and photosynthetic capacity including increased reducing power, starch synthesis and sucrose mobilization under elevated CO2. Overall, our data on physiological and transcriptomic analyses suggest an optimal resource allocation to the available and developing sink organs thereby sustaining improved photosynthetic rates during long-term growth of Jatropha under CO2 enriched environment.

Unravelling molecular mechanisms from floral initiation to lipid biosynthesis in a promising biofuel tree species, Pongamia pinnata using transcriptome analysis

Pongamia pinnata (L.) (Fabaceae) is a promising biofuel tree species which is underexploited in the areas of both fundamental and applied research, due to the lack of information either on transcriptome or genomic data. To investigate the possible metabolic pathways, we performed whole transcriptome analysis of Pongamia through Illumina NextSeq platform and generated 2.8 GB of paired end sequence reads. The de novo assembly of raw reads generated 40,000 contigs and 35,000 transcripts, representing leaf, flower and seed unigenes. Spatial and temporal expression profiles of photoperiod and floral homeotic genes in Pongamia, identified GIGANTEA (GI) - CONSTANS (CO) - FLOWERING LOCUS T (FT) as active signal cascade for floral initiation. Four prominent stages of seed development were selected in a high yielding Pongamia accession (TOIL 1) to follow the temporal expression patterns of key fatty acid biosynthetic genes involved in lipid biosynthesis and accumulation. Our results provide insights into an array of molecular events from flowering to seed maturity in Pongamia which will provide substantial basis for modulation of fatty acid composition and enhancing oil yields which should serve as a potential feedstock for biofuel production.

Implications of High Temperature and Elevated CO2 on Flowering Time in Plants

Flowering is a crucial determinant for plant reproductive success and seed-set. Increasing temperature and elevated carbon-dioxide (e[CO2]) are key climate change factors that could affect plant fitness and flowering related events. Addressing the effect of these environmental factors on flowering events such as time of day of anthesis (TOA) and flowering time (duration from germination till flowering) is critical to understand the adaptation of plants/crops to changing climate and is the major aim of this review. Increasing ambient temperature is the major climatic factor that advances flowering time in crops and other plants, with a modest effect of e[CO2].Integrated environmental stimuli such as photoperiod, temperature and e[CO2] regulating flowering time is discussed. The critical role of plant tissue temperature influencing TOA is highlighted and crop models need to substitute ambient air temperature with canopy or floral tissue temperature to improve predictions. A complex signaling network of flowering regulation with change in ambient temperature involving different transcription factors (PIF4, PIF5), flowering suppressors (HvODDSOC2, SVP, FLC) and autonomous pathway (FCA, FVE) genes, mainly from Arabidopsis, provides a promising avenue to improve our understanding of the dynamics of flowering time under changing climate. Elevated CO2 mediated changes in tissue sugar status and a direct [CO2]-driven regulatory pathway involving a key flowering gene, MOTHER OF FT AND TFL1 (MFT), are emerging evidence for the role of e[CO2] in flowering time regulation.

Stage-Specific Fatty Acid Fluxes Play a Regulatory Role in Glycerolipid Metabolism during Seed Development in Jatropha curcas L

The present study describes the changes in lipid profile as well as fatty acid fluxes during seed development in Jatropha curcas L. Endosperm from 34, 37, and 40 days after anthesis (DAA), incubated with [(14)C]acetate, showed significant synthesis of phosphatidylcholine (PC) at seed maturation. The fatty acid methyl ester profile showed PC from 34 DAA was rich in palmitic acid (16:0), whereas PC from 37 and 40 DAA was rich in oleic acid (18:1n-9). Molecular species analysis of diacylglycerol (DAG) indicated DAG (16:0/18:2n-6) was in abundance at 34 DAA, whereas DAG (18:1n-9/18:2n-6) was significantly high at 40 DAA. Triacylglycerol (TAG) analysis revealed TAG (16:0/18:2n-6/16:0) was abundant at 34 DAA, whereas TAG (18:1n-9/18:2n-6/18:1n-9) formed the majority at 40 DAA. Expression of two types of diacylglycerol acyltransferases varied with seed maturation. These data demonstrate stage-specific distinct pools of PC and DAG synthesis during storage TAG accumulation in Jatropha seed.