C3 Crop Plants Research Articles

Response of maize (Zea mays L.) on yield, physiology and stomatal behaviour under two different elevated CO<sub>2</sub> concentrations. Do these anatomical changes affect the physiology of the C4 crop plant under high CO<sub>2</sub> conditions?

Response of maize (Zea mays L.) on yield, physiology and stomatal behaviour under two different elevated CO<sub>2</sub> concentrations. Do these anatomical changes affect the physiology of the C4 crop plant under high CO<sub>2</sub> conditions?

SAGA1 and SAGA2 promote starch formation around proto-pyrenoids in Arabidopsis chloroplasts

The pyrenoid is a chloroplastic microcompartment in which most algae and some terrestrial plants condense the primary carboxylase, Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) as part of a CO2-concentrating mechanism that improves the efficiency of CO2 capture. Engineering a pyrenoid-based CO2-concentrating mechanism (pCCM) into C3 crop plants is a promising strategy to enhance yield capacities and resilience to the changing climate. Many pyrenoids are characterized by a sheath of starch plates that is proposed to act as a barrier to limit CO2 diffusion. Recently, we have reconstituted a phase-separated "proto-pyrenoid" Rubisco matrix in the model C3 plant Arabidopsis thaliana using proteins from the alga with the most well-studied pyrenoid, Chlamydomonas reinhardtii [N. Atkinson, Y. Mao, K. X. Chan, A. J. McCormick, Nat. Commun. 11, 6303 (2020)]. Here, we describe the impact of introducing the Chlamydomonas proteins StArch Granules Abnormal 1 (SAGA1) and SAGA2, which are associated with the regulation of pyrenoid starch biogenesis and morphology. We show that SAGA1 localizes to the proto-pyrenoid in engineered Arabidopsis plants, which results in the formation of atypical spherical starch granules enclosed within the proto-pyrenoid condensate and adjacent plate-like granules that partially cover the condensate, but without modifying the total amount of chloroplastic starch accrued. Additional expression of SAGA2 further increases the proportion of starch synthesized as adjacent plate-like granules that fully encircle the proto-pyrenoid. Our findings pave the way to assembling a diffusion barrier as part of a functional pCCM in vascular plants, while also advancing our understanding of the roles of SAGA1 and SAGA2 in starch sheath formation and broadening the avenues for engineering starch morphology.

Growth and physiological response of canola (Brassica napus L.) tointeractive effect of temperature, moisture and nitrogen stressesunder controlled environment

Present atmospheric limits growth of C3 crop plants, which show response to elevated CO2 via reduced photorespiration and enhanced photosynthetic rates thereby increased growth and yield. Global research on plant responses to raising atmospheric CO2 has primarily focused on C3 species, advancing our understanding of processes underlying C3 plant acclimation and response. Therefore extensive research has been conducted to project the potential impacts of global warming on agriculture productivity through laboratory by using crop and global climate models. Canola is one of the world’s most important oilseed crops and the most profitable commodity for Canadian farmers. As a C3 cool seasoncrop, it is more susceptible to heat stress than other C3 and C4 field crops (Wu and Ma, 2018). High temperature significantly changes the rate of plant metabolic processes that ultimately reduces biomass accumulation and grainformation. A field study in Eastern Canada reported that seed yield reduced as much as 40% in 2012 due to severeheat and drought stress over normal years (Ma and Herath, 2016). High or warm temperature has been shown toinduce the floral sterility or pollen abortion and shorten seed filling duration and subsequently reduce inflorescence size in canola plants. Even high temperature could alter the partitioning of photoassimilates to roots and suppress root growth extension or change root system architecture. Late seeded canola plants often produced a smaller root system, due to higher temperature and or drought stress encounters during the crop development. Keeping these facts trial was conducted under controlled condition to know the response of canola to drought stress, elevated CO2 and temperature.

Molecular genetic markers associated with saltpans effluents (NaCl stress) on Cajanus cajan C3 plant and Sorghum bicolor C4 crop plants at four different agricultural fields

Molecular genetic markers associated with saltpans effluents (NaCl stress) on Cajanus cajan C3 plant and Sorghum bicolor C4 crop plants at four different agricultural fields

MYB Transcription Factor Family in Pearl Millet: Genome-Wide Identification, Evolutionary Progression and Expression Analysis under Abiotic Stress and Phytohormone Treatments.

Transcription factors (TFs) are the regulatory proteins that act as molecular switches in controlling stress-responsive gene expression. Among them, the MYB transcription factor family is one of the largest TF family in plants, playing a significant role in plant growth, development, phytohormone signaling and stress-responsive processes. Pearl millet (Pennisetum glaucum L.) is one of the most important C4 crop plants of the arid and semi-arid regions of Africa and Southeast Asia for sustaining food and fodder production. To explore the evolutionary mechanism and functional diversity of the MYB family in pearl millet, we conducted a comprehensive genome-wide survey and identified 279 MYB TFs (PgMYB) in pearl millet, distributed unevenly across seven chromosomes of pearl millet. A phylogenetic analysis of the identified PgMYBs classified them into 18 subgroups, and members of the same group showed a similar gene structure and conserved motif/s pattern. Further, duplication events were identified in pearl millet that indicated towards evolutionary progression and expansion of the MYB family. Transcriptome data and relative expression analysis by qRT-PCR identified differentially expressed candidate PgMYBs (PgMYB2, PgMYB9, PgMYB88 and PgMYB151) under dehydration, salinity, heat stress and phytohormone (ABA, SA and MeJA) treatment. Taken together, this study provides valuable information for a prospective functional characterization of the MYB family members of pearl millet and their application in the genetic improvement of crop plants.

A dynamic phosphoproteomic analysis provides insight into the C4 plant maize (Zea mays L.) response to natural diurnal changes.

As sessile organisms, plants need to respond to rapid changes in numerous environmental factors, mainly diurnal changes of light, temperature, and humidity. Maize is the world's most grown crop, and as a C4 plant it exhibits high photosynthesis capacity, reaching the highest rate of net photosynthesis at midday; that is, there is no "midday depression." Revealing the physiological responses to diurnal changes and underlying mechanisms will be of great significance for guiding maize improvement efforts. In this study, we collected maize leaf samples and analyzed the proteome and phosphoproteome at nine time points during a single day/night cycle, quantifying 7424 proteins and 5361 phosphosites. The new phosphosites identified in our study increased the total maize phosphoproteome coverage by 8.5%. Kinase-substrate network analysis indicated that 997 potential substrates were phosphorylated by 20 activated kinases. Through analysis of proteins with significant changes in abundance and phosphorylation, we found that the response to a heat stimulus involves a change in the abundance of numerous proteins. By contrast, the high light at noon and rapidly changing light conditions induced changes in the phosphorylation level of proteins involved in processes such as chloroplast movement, photosynthesis, and C4 pathways. Phosphorylation is involved in regulating the activity of large number of enzymes; for example, phosphorylation of S55 significantly enhanced the activity of maize phosphoenolpyruvate carboxykinase1 (ZmPEPCK1). Overall, the database of dynamic protein abundance and phosphorylation we have generated provides a resource for the improvement of C4 crop plants.

Efficient genome editing and gene knockout in Setaria viridis with CRISPR/Cas9 directed gene editing by the non-homologous end-joining pathway.

The CRISPR/Cas9 system has been used for genome editing in several organisms, including higher plants. This system induces site-specific mutations in the genome based on the nucleotide sequence of engineered guide RNAs. The complex genomes of C4 grasses makes genome editing a challenge in key grass crops like maize (Zea mays), sorghum (Sorghum bicolor), Brachiaria spp., switchgrass (Panicum virgatum), and sugarcane (Saccharum spp.). Setaria viridis is a diploid C4 grass widely used as a model for these C4 crop plants. Here, an optimized CRISPR/Cas9 binary vector that exploits the non-homologous end joining (NHEJ) system was used to knockout a green fluorescent protein (gfp) transgene in S. viridis accession A10.1. Transformation of embryogenic callus by A. tumefaciens generated ten glufosinate-ammonium resistant transgenic events. In the T0 generation, 60% of the events were biallelic mutants in the gfp transgene with no detectable accumulation of GFP protein and without insertions or deletions in predicted off-target sites. The gfp mutations generated by CRISPR/Cas9 were stable and displayed Mendelian segregation in the T1 generation. Altogether, the system described here is a highly efficient genome editing system for S. viridis, an important model plant for functional genomics studies in C4 grasses. Also, this system is a potential tool for improvement of agronomic traits in C4 crop plants with complex genomes.

Validation of an Enzyme-Driven Model Explaining Photosynthetic Rate Responses to Limited Nitrogen in Crop Plants.

The limited availability of nitrogen (N) is a fundamental challenge for many crop plants. We have hypothesized that the relative crop photosynthetic rate (P) is exponentially constrained by certain plant-specific enzyme activities, such as ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), NADP-glyceraldehyde-3-phosphate dehydrogenase (NADP-G3PDH), 3-phosphoglyceric acid (PGA) kinase, and chloroplast fructose-1,6-bisphosphatase (cpFBPase), in Triticum aestivum and Oryza sativa. We conducted a literature search to compile information from previous studies on C3 and C4 crop plants, to examine the photosynthetic rate responses to limited leaf [N] levels. We found that in Zea mays, NADP-malic enzyme (NADP-ME), PEP carboxykinase (PCK), and Rubisco activities were positively correlated with P. A positive correlation was also observed between both phosphoenolpyruvate carboxylase (PEPC) and Rubisco activity with leaf [N] in Sorghum bicolor. Key enzyme activities responded differently to P in C3 and C4 plants, suggesting that other factors, such as leaf [N] and the stage of leaf growth, also limited specific enzyme activities. The relationships followed the best fitting exponential relationships between key enzymes and the P rate in both C3 and C4 plants. It was found that C4 species absorbed less leaf [N] but had higher [N] assimilation rates (A rate) and higher maximum photosynthesis rates (Pmax), i.e., they were able to utilize and invest more [N] to sustain higher carbon gains. All C3 species studied herein had higher [N] storage (Nstore) and higher absorption of [N], when compared with the C4 species. Nstore was the main [N] source used for maintaining photosynthetic capacity and leaf expansion. Of the nine C3 species assessed, rice had the greatest Pmax, thereby absorbing more leaf [N]. Elevated CO2 (eCO2) was also found to reduce the leaf [N] and Pmax in rice but enhanced the leaf [N] and N use efficiency of photosynthesis in maize. We concluded that eCO2 affects [N] allocation, which directly or indirectly affects Pmax. These results highlight the need to further study these physiological and biochemical processes, to better predict how crops will respond to eCO2 concentrations and limited [N].

Comprehensive phylogenomic analysis of ERF genes in sorghum provides clues to the evolution of gene functions and redundancy among gene family members.

APETALA2/Ethylene-Responsive transcription factors (AP2/ERF), with their multifunctional roles in plant development, hormone signaling and stress tolerance, are important candidates for engineering crop plants. Here, we report identification and analysis of gene structure, phylogenetic distribution, expression, chromosomal localization and cis-acting promoter analysis of AP2/ERF genes in the C4 crop plant sorghum. We identified 158 ERF genes in sorghum with 52 of them encoding dehydration-responsive binding elements (DREB) while 106 code for ERF subfamily proteins. Phylogenetic analysis organized sorghum ERF proteins into 11 distinct groups exhibiting clade-specific expansion. About 68% ERF genes have paralogs indicating gene duplications as major cause of expansion of ERF family in sorghum. Analysis of spatiotemporal expression patterns using publicly available data revealed their tissue/genotype-preferential accumulation. In addition, 40 ERF genes exhibited differential accumulation in response to heat and/or drought stress. About 25% of the segmental gene pairs and eleven tandem duplicated genes exhibited high correlation (> 0.7) in their expression patterns indicating genetic redundancy. Comparative phylogenomic analysis of sorghum ERFs with 74 genetically characterized ERF genes from other plant species provided significant clues to sorghum ERF functions. Overall data generated here provides an overview of evolutionary relationship among ERF gene family members in sorghum and with respect to previously characterized ERF genes from other plant species. This information will be instrumental in initiating functional genomic studies of ERF candidates in sorghum.

Biosystems Design to Accelerate C3-to-CAM Progression.

Global demand for food and bioenergy production has increased rapidly, while the area of arable land has been declining for decades due to damage caused by erosion, pollution, sea level rise, urban development, soil salinization, and water scarcity driven by global climate change. In order to overcome this conflict, there is an urgent need to adapt conventional agriculture to water-limited and hotter conditions with plant crop systems that display higher water-use efficiency (WUE). Crassulacean acid metabolism (CAM) species have substantially higher WUE than species performing C3 or C4 photosynthesis. CAM plants are derived from C3 photosynthesis ancestors. However, it is extremely unlikely that the C3 or C4 crop plants would evolve rapidly into CAM photosynthesis without human intervention. Currently, there is growing interest in improving WUE through transferring CAM into C3 crops. However, engineering a major metabolic plant pathway, like CAM, is challenging and requires a comprehensive deep understanding of the enzymatic reactions and regulatory networks in both C3 and CAM photosynthesis, as well as overcoming physiometabolic limitations such as diurnal stomatal regulation. Recent advances in CAM evolutionary genomics research, genome editing, and synthetic biology have increased the likelihood of successful acceleration of C3-to-CAM progression. Here, we first summarize the systems biology-level understanding of the molecular processes in the CAM pathway. Then, we review the principles of CAM engineering in an evolutionary context. Lastly, we discuss the technical approaches to accelerate the C3-to-CAM transition in plants using synthetic biology toolboxes.

Effect of salt tolerance on biomass production in a large population of sorghum accessions.

Salinity causes major reductions in cultivated land area, crop productivity, and crop quality, and salt-tolerant crops have been required to sustain agriculture in salinized areas. The annual C4 crop plant Sorghum bicolor (L.) Moench is salt tolerant, with large variation among accessions. Sorghum’s salt tolerance is often evaluated during early growth, but such evaluations are weakly related to overall performance. Here, we evaluated salt tolerance of 415 sorghum accessions grown in saline soil (0, 50, 100, and 150 mM NaCl) for 3 months. Some accessions produced up to 400 g per plant of biomass and showed no growth inhibition at 50 mM NaCl. Our analysis indicated that the genetic factors that affected biomass production under 100 mM salt stress were more different from those without salt stress, comparing to the differences between those under 50 mM and 100 mM salt stress. A genome-wide association study for salt tolerance identified two single-nucleotide polymorphisms (SNPs) that were significantly associated with biomass production, only at 50 mM NaCl. Additionally, two SNPs were significantly associated with salt tolerance index as an indicator for growth response of each accession to salt stress. Our results offer candidate genetic resources and SNP markers for breeding salt-tolerant sorghum.

Arbuscular mycorrhizal fungal diversity increases growth and phosphorus uptake in C3 and C4 crop plants

Most plants associate with arbuscular mycorrhizal (AM) fungi which can enhance their growth and nutrient uptake. Outcomes of the AM symbiosis can be highly variable, depending on soil fertility, plant functional group (C3, C4) and AM fungal diversity. This study assessed the growth and nutrient (C, N, P) responses of two C3 (Triticum aestivum and Hordeum vulgare) and two C4 (Sorghum bicolor and Zea mays) plants to different AM fungal inocula (no AM fungi, single AM fungal species, and four AM fungal species) under high and low P conditions. Higher AM fungal diversity resulted in greater P concentration and aboveground biomass of H. vulgare and S. bicolor. Triticum aestivum did not respond to AM fungi, while Z. mays responded positively but a similar positive response of Z. mays growth and nutrition occured when it was colonised with single or multiple AM fungal species. These findings suggest that, although C3 crop plants are less responsive to AM fungi than C4, some C3 and C4 species can benefit from higher AM fungal diversity in the soil.

Overexpressing the most abundant enzyme.

Plants’ photosynthetic capacity at high light is limited by the kinetics of the slow, carbon-dioxide-fixing enzyme Rubisco. Increasing Rubisco content in a C4 crop plant is now shown to enhance photosynthesis and growth.

Plant-Aphid Interactions Under Elevated CO2: Some Cues from Aphid Feeding Behavior.

Although the increasing concentration of atmospheric carbon dioxide (CO2) accelerates the accumulation of carbohydrates and increases the biomass and yield of C3 crop plants, it also reduces their nitrogen concentration. The consequent changes in primary and secondary metabolites affect the palatability of host plants and the feeding of herbivorous insects. Aphids are phloem feeders and are considered the only feeding guild that positively responds to elevated CO2. In this review, we consider how elevated CO2 modifies host defenses, nutrients, and water-use efficiency by altering concentrations of the phytohormones jasmonic acid, salicylic acid, ethylene, and abscisic acid. We will describe how these elevated CO2-induced changes in defenses, nutrients, and water statusfacilitate specific stages of aphid feeding, including penetration, phloem-feeding, and xylem absorption. We conclude that a better understanding of the effects of elevated CO2 on aphids and on aphid damage to crop plants will require research on the molecular aspects of the interaction between plant and aphid but also research on aphid interactions with their intra- and inter-specific competitors and with their natural enemies.

Yield Characteristics Of Melissa Officinalis L. In Response To The Foliar Application Of Methanol And Ethanol Solutions

Lemon balm, one of the important medicinal plant species mainly grown in natural flora, especially in the Mediterranean region of Turkey, is native to southern Europe and northern Africa, and east as far as the Caucasus and northern Iran [1]. Short chain alcohols such as ethanol and methanol are reported to enhance biomass accumulation and seed germination for several C3 crop species [2]. Foliar sprays of aqueous 10 – 50% methanol increased growth and development of C3 crop plants [3]. The aims of this study were evaluation of the yield characteristics of lemon balm in response to the methanol and ethanol solutions as a new and safe technology in production of medicinal plants, based on a randomized complete block design with 12 treatments and 3 replications in the experimental field of Institute of Medicinal Plants (IMP) in Karaj at 2010. The treatments of this study include: control (distilled and without distilled water), ethanol and methanol aqueous solutions each one of them with 10, 20, 30, 40 and 50% (v/v). The results were indicated that the effects of hydroalcoholic solutions had significant differences (P < 0.01) on 15 agronomical and morphophysiological traits. The results indicated that the most amount of plant height in methanol 30%, stem diameter, stem number, stem fresh weight, stem dry weight, leaf number, leaf area, leaf fresh weight, leaf weight, shoot fresh weight, shoot dry weight, seed weight per plant and essential oil yield in methanol 40%, chlorophyll content and thousand seed weight in methanol 50% were obtained.

The Road to C4Photosynthesis: Evolution of a Complex Trait via Intermediary States

C4 photosynthesis enables high photosynthetic energy conversion efficiency as well as high nitrogen and water use efficiencies. Given the multitude of biochemical, structural and molecular changes in comparison with C3 photosynthesis, it appears unlikely that such a complex trait would evolve in a single step. C4 photosynthesis is therefore believed to have evolved from the ancestral C3 state via intermediary stages. Consequently, the identification and detailed characterization of plant species representing transitory states between C3 and C4 is important for the reconstruction of the sequence of evolutionary events, especially since C4 evolution occurred in very different phylogenetic backgrounds. There is also significant interest in engineering of C4 or at least C4-like elements into C3 crop plants. A detailed and mechanistic understanding of C3-C4 intermediates is likely to provide guidance for the experimental design of such approaches. Here we provide an overview on the most relevant results obtained on C3-C4 intermediates to date. Recent knowledge gains in this field will be described in more detail. We thereby concentrate especially on biochemical and physiological work. Finally, we will provide a perspective and outlook on the continued importance of research on C3-C4 intermediates.

Sun-to-Wheels Exergy Efficiencies for Bio-Ethanol and Photovoltaics.

The two main paths to power vehicles with sunlight are to use photosynthesis to grow biomass, converting to a liquid fuel for an internal combustion engine or to generate photovoltaic electricity that powers the battery of an electric vehicle. While the environmental attributes of these two paths have been much analyzed, prior studies consider the current state of technology. Technologies for biofuel and photovoltaic paths are evolving; it is critical to consider how progress might improve environmental performance. We address this challenge by assessing the current and maximum theoretical exergy efficiencies of bioethanol and photovoltaic sun-to-wheels process chains. The maximum theoretical efficiency is an upper bound stipulated by physical laws. The current net efficiency to produce motive power from silicon photovoltaic modules is estimated at 5.4%, much higher than 0.03% efficiency for corn-based ethanol. Flat-plate photovoltaic panels also have a much higher theoretical maximum efficiency than a C4 crop plant, 48% versus 0.19%. Photovoltaic-based power will always be vastly more efficient than a terrestrial crop biofuel. Providing all mobility in the U.S. via crop biofuels would require 130% of arable land with current technology and 20% in the thermodynamic limit. Comparable values for photovoltaic-based power are 0.7% and 0.081%, respectively.

Differential improvement in transpiration efficiency of C3 and C4 crop plants under elevated CO2 conditions

Sunflower plants (C3) transpired more water than pearl millet (C4) from seedling to maturity under ambient conditions. The transpiration (water use) at elevated CO2 was lesser for pearl millet and higher for sunflower compared to ambient. Elevated atmospheric CO2 increased TE more in pearl millet (21.9%) than in sunflower (10.5%) and decreased the TR or water transpired to produce dry mass by 18.1% in pearl millet and 9.7% in sunflower compared to ambient. As the CO2 content of the air continues to rise, both sunflower (C3) and pearl millet (C4) agriculture crops will respond favorably by exhibiting increases in TE.

The cyanobacterial CCM as a source of genes for improving photosynthetic CO2 fixation in crop species

Crop yields need to nearly double over the next 35 years to keep pace with projected population growth. Improving photosynthesis, via a range of genetic engineering strategies, has been identified as a promising target for crop improvement with regard to increased photosynthetic yield and better water-use efficiency (WUE). One approach is based on integrating components of the highly efficient CO(2)-concentrating mechanism (CCM) present in cyanobacteria (blue-green algae) into the chloroplasts of key C(3) crop plants, particularly wheat and rice. Four progressive phases towards engineering components of the cyanobacterial CCM into C(3) species can be envisaged. The first phase (1a), and simplest, is to consider the transplantation of cyanobacterial bicarbonate transporters to C(3) chloroplasts, by host genomic expression and chloroplast targeting, to raise CO(2) levels in the chloroplast and provide a significant improvement in photosynthetic performance. Mathematical modelling indicates that improvements in photosynthesis as high as 28% could be achieved by introducing both of the single-gene, cyanobacterial bicarbonate transporters, known as BicA and SbtA, into C(3) plant chloroplasts. Part of the first phase (1b) includes the more challenging integration of a functional cyanobacterial carboxysome into the chloroplast by chloroplast genome transformation. The later three phases would be progressively more elaborate, taking longer to engineer other functional components of the cyanobacterial CCM into the chloroplast, and targeting photosynthetic and WUE efficiencies typical of C(4) photosynthesis. These later stages would include the addition of NDH-1-type CO(2) pumps and suppression of carbonic anhydrase and C(3) Rubisco in the chloroplast stroma. We include a score card for assessing the success of physiological modifications gained in phase 1a.

The prospect of using cyanobacterial bicarbonate transporters to improve leaf photosynthesis in C3 crop plants.

The photosynthetic CO2-fixing enzyme Rubisco arose some 3.5 billion years ago, in an environment when CO2 was high and oxygen (O2) was low. Under these conditions, it was CO2 saturated and presumably performed well ([Badger et al., 1998][1]). However, since the advent of oxygenic photosynthesis, the