Morphophysiological alterations in transgenic rice lines expressing PPDK and ME genes from the C4 model Setaria italica

Optimization strategies to improve the carbon sink capacity of C3 plants under the background of dual carbon strategy

In the 21st century, mankind is facing serious climate challenges, and the greenhouse effect caused by excessive CO2 emissions is a difficult problem that mankind urgently needs to solve. In this context, the dual-carbon strategy is proposed, that is, it is hoped that by reducing carbon sources and increasing carbon sinks, the purpose of improving the climate can be achieved. Plants themselves have a certain carbon sequestration capacity, and C4 plants have a stronger carbon sequestration capacity than C3. Therefore, it is a good research prospect to improve C3 plants by utilizing the relevant characteristics of C4 plants to enhance the CO2 absorption capacity of C3 plants. Current research is generally focused on genetic engineering, this paper summarizes the enzymes that have some research significance in C3 plant modification, such as, Rubisco, PPDK, PEPC, NADP-MDH, NADP-ME, etc., as well as the related genes that constitute the enzymes, and also outlines a series of recent advances in the modification of photorespiratory branching and non-photochemical quenching (NPQ). It is hoped that this paper will provide certain research directions and ideas for researchers to obtain C3 plants with higher carbon sequestration capacity.

Synthetic crassulacean acid metabolism (SynCAM) for improving water-use efficiency in plants

The global climate crisis will continue to increase the frequency and duration of drought episodes in agricultural production areas worldwide. Hot and dry conditions create greater water-deficit stresses on crops, lowering their productivity. While multiple engineering strategies have been developed to improve the efficiency of photosynthesis, greater efforts are needed to improve the drought attenuation and water-use efficiency of crops. Crassulacean acid metabolism (CAM) is a naturally occurring elaboration of C3 photosynthesis that allows plants to occupy and thrive in hot and dry environments with limited or intermittent water supply. Creating synthetic versions of bioengineered CAM is one potentially fruitful approach to improving crop productivity while also reducing photorespiration and increasing water-use efficiency. We outline current efforts being undertaken to engineer CAM-like or synthetic versions of CAM (SynCAM) and future advances and strategies that might contribute to the optimization of SynCAM engineering in crops.This article is part of the theme issue 'Crops under stress: can we mitigate the impacts of climate change on agriculture and launch the 'Resilience Revolution'?'.

C4 cereal and biofuel crop microbiomes

Microbiomes provide multiple life-support functions for plants, including nutrient acquisition and tolerance to abiotic and biotic stresses. Considering the importance of C4 cereal and biofuel crops for food security under climate change conditions, more attention has been given recently to C4 plant microbiome assembly and functions. Here, we review the current status of C4 cereal and biofuel crop microbiome research with a focus on beneficial microbial traits for crop growth and health. We highlight the importance of environmental factors and plant genetics in C4 crop microbiome assembly and pinpoint current knowledge gaps. Finally, we discuss the potential of foxtail millet as a C4 model species and outline future perspectives of C4 plant microbiome research.

In vitro induction of tetraploids and their phenotypic and transcriptome analysis in Glehnia littoralis

BACKGROUND

Glehnia littoralis is a medicinal and edible plant species having commercial value and has several hundred years of cultivation history. Polyploid breeding is one of the most important and fastest ways to generate novel varieties. To obtain tetraploids of G. littoralis in vitro, colchicine treatment was given to the seeds and then were screened based on morphology, flow cytometry, and root tip pressing assays. Furthermore, transcriptome analysis was performed to identity the differentially expressed genes associated with phenotypic changes in tetraploid G. littoralis.

RESULTS

The results showed that 0.05% (w/v) colchicine treatment for 48 h was effective in inducing tetraploids in G. littoralis. The tetraploid G. littoralis (2n = 4x = 44) was superior in leaf area, leaf thickness, petiole diameter, SPAD value (Chl SPAD), stomatal size, epidermal tissues thickness, palisade tissues thickness, and spongy tissues thickness to the diploid ones, while the stomatal density of tetraploids was significantly lower. Transcriptome sequencing revealed, a total of 1336 differentially expressed genes (DEGs) between tetraploids and diploids. Chromosome doubling may lead to DNA content change and gene dosage effect, which directly affects changes in quantitative traits, with changes such as increased chlorophyll content, larger stomata and thicker tissue of leaves. Several up-regulated DEGs were found related to growth and development in tetraploid G. littoralis such as CKI, PPDK, hisD and MDP1. KEGG pathway enrichment analyses showed that most of DEGs were enriched in metabolic pathways.

CONCLUSIONS

This is the first report of the successful induction of tetraploids in G. littoralis. The information presented in this study facilitate breeding programs and molecular breeding of G. littoralis varieties.

Morphological change and genome-wide transcript analysis of Haloxylon ammodendron leaf development reveals morphological characteristics and genes associated with the different C3 and C4 photosynthetic metabolic pathways

C4 photosynthesis outperforms C3 photosynthesis in natural ecosystems by maintaining a high photosynthetic rate and affording higher water-use and nitrogen-use efficiencies. C4 plants can survive in environments with poor living conditions, such as high temperatures and arid regions, and will be crucial to ecological and agricultural security in the face of global climate change in the future. However, the genetic architecture of C4 photosynthesis remains largely unclear, especially the genetic regulation of C4 Kranz anatomy. Haloxylon ammodendron is an important afforestation tree species and a valuable C4 wood plant in the desert region. The unique characteristic of H. ammodendron is that, during the seedling stage, it utilizes C3 photosynthesis, while in mature assimilating shoots (maAS), it switches to the C4 pathway. This makes an exceptional opportunity for studying the development of the C4 Kranz anatomy and metabolic pathways within individual plants (identical genome). To provide broader insight into the regulation of Kranz anatomy and non-Kranz leaves of the C4 plant H. ammodendron, carbon isotope values, anatomical sections and transcriptome analyses were used to better understand the molecular and cellular processes related to the development of C4 Kranz anatomy. This study revealed that H. ammodendron conducts C3 in the cotyledon before it switches to C4 in AS. However, the switching requires a developmental process. Stable carbon isotope discrimination measurements on three different developmental stages showed that young AS have a C3-like δ13C even though C4 Kranz anatomy is found, which is inconsistent with the anatomical findings. A C4-like δ13C can be measured in AS until they are mature. The expression analysis of C4 key genes also showed that the maAS exhibited higher expression than the young AS. In addition, many genes that may be related to the development of Kranz anatomy were screened. Comparison of gene expression patterns with respect to anatomy during leaf ontogeny provided insight into the genetic features of Kranz anatomy. This study helps with our understanding of the development of Kranz anatomy and provides future directions for studies on key C4 regulatory genes.

C4 rice engineering, beyond installing a C4 cycle

C4 photosynthesis in higher plants is carried out by two distinct cell types: mesophyll cells and bundle sheath cells, as a result highly concentrated carbon dioxide is released surrounding RuBisCo in chloroplasts of bundle sheath cells and the photosynthetic efficiency is significantly higher than that of C3 plants. The evolution of the dual-cell C4 cycle involved complex modifications to leaf anatomy and cell ultra-structures. These include an increase in leaf venation, the formation of Kranz anatomy, changes in chloroplast morphology in bundle sheath cells, and increases in the density of plasmodesmata at interfaces between the bundle sheath and mesophyll cells. It is predicted that cereals will be in severe worldwide shortage at the mid-term of this century. Rice is a staple food that feeds more than half of the world's population. If rice can be engineered to perform C4 photosynthesis, it is estimated that rice yield will be increased by at least 50% due to enhanced photosynthesis. Thus, the Second Green Revolution has been launched on this principle by genetically installing C4 photosynthesis into C3 crops. The studies on molecular mechanisms underlying the changes in leaf morphoanatomy involved in C4 photosynthesis have made great progress in recent years. As there are plenty of reviews discussing the installment of the C4 cycle, we focus on the current progress and challenges posed to the research regarding leaf anatomy and cell ultra-structure modifications made towards the development of C4 rice.

Overexpression of chloroplastic Zea mays NADP-malic enzyme (ZmNADP-ME) confers tolerance to salt stress in Arabidopsis thaliana

The C4 plants photosynthesize better than C3 plants especially in arid environment. As an attempt to genetically convert C3 plant to C4, the cDNA of decarboxylating C4 type NADP-malic enzyme from Zea mays (ZmNADP-ME) that has lower Km for malate and NADP than its C3 isoforms, was overexpressed in Arabidopsis thaliana under the control of 35S promoter. Due to increased activity of NADP-ME in the transgenics the malate decarboxylation increased that resulted in loss of carbon skeletons needed for amino acid and protein synthesis. Consequently, amino acid and protein content of the transgenics declined. Therefore, the Chl content, photosynthetic efficiency (Fv/Fm), electron transport rate (ETR), the quantum yield of photosynthetic CO2 assimilation, rosette diameter, and biomass were lower in the transgenics. However, in salt stress (150 mM NaCl), the overexpressers had higher Chl, protein content, Fv/Fm, ETR, and biomass than the vector control. NADPH generated in the transgenics due to increased malate decarboxylation, contributed to augmented synthesis of proline, the osmoprotectant required to alleviate the reactive oxygen species-mediated membrane damage and oxidative stress. Consequently, the glutathione peroxidase activity increased and H2O2 content decreased in the salt-stressed transgenics. The reduced membrane lipid peroxidation and lower malondialdehyde production resulted in better preservation, of thylakoid integrity and membrane architecture in the transgenics under saline environment. Our results clearly demonstrate that overexpression of C4 chloroplastic ZmNADP-ME in the C3 Arabidopsis thaliana, although decrease their photosynthetic efficiency, protects the transgenics from salinity stress.

Overexpression of Setaria italica phosphoenolpyruvate carboxylase gene in rice positively impacts photosynthesis and agronomic traits

C₄ plants have the inherent capacity to concentrate atmospheric CO₂ in the vicinity of RuBisCo, thereby increasing carboxylation, and inhibiting photorespiration. Carbonic anhydrase (CA), the first enzyme of C₄ photosynthesis, converts atmospheric CO₂ to HCO₃^-, which is utilized by PEPC to produce C₄ acids. Bioengineering of C₄ traits into C₃ crops is an attractive strategy to increase photosynthesis and water use efficiency. In the present study, we isolated the PEPC gene from the C₄ plant Setaria italica and transferred it to C₃ rice. Overexpression of SiPEPC resulted in a 2-6-fold increment in PEPC enzyme activity in transgenic lines with respect to non-transformed control. Photosynthetic efficiency was enhanced in transformed plants, which was associated with increased ФPSII, ETR, lower NPQ, and higher chlorophyll accumulation. Water use efficiency was increased by 16-22% in PEPC transgenic rice lines. Increased PEPC activity enhanced quantum yield and carboxylation efficiency of PEPC transgenic lines. Transgenic plants exhibited higher light saturation photosynthesis rate and lower CO₂ compensation point, as compared to non-transformed control. An increase in net photosynthesis increased the yield by (23-28.9%) and biomass by (24.1-29%) in transgenic PEPC lines. Altogether, our findings indicate that overexpression of C_4-specific SiPEPC enzyme is able to enhance photosynthesis and related parameters in transgenic rice.

Effects of exogenous Strigolactone on the physiological and ecological characteristics of Pennisetum purpureum Schum. Seedlings under drought stress

BACKGROUND

Drought is one of the main environmental factors limiting plant growth and development. Pennisetum purpureum Schum. was used to explore the mitigation effects of exogenous strigolactone (SL) on drought stress during the seedling stage. The effects of different concentrations (1, 3, 5, and 7 μmol·L^- 1) of SL on the photosynthesis characteristics, growth performance, and endogenous abscisic acid (ABA) of P. purpureum under drought stress were studied.

RESULTS

Exogenous SL could effectively alleviate the inhibitory effect of drought stress on P. purpureum growth. Compared with drought stress, the net photosynthesis rate, stomatal conductance, transpiration rate, and water-use efficiency of the leaves of P. purpureum after SL treatment significantly increased, thereby exerting a significant mitigation effect on the decrease in photosystem II maximum photochemical efficiency and the performance index based on light absorption caused by drought. Moreover, the exogenous application of SL can effectively increase the fresh and dry weight of the leaves and roots and the main-root length. After applying SL for 120 h, the ABA content of P. purpureum decreased significantly. The activity of key enzymes of photosynthesis significantly increased after 48 h of external application of SL to P. purpureum.

CONCLUSIONS

SL treatment can improve the photosynthesis performance of P. purpureum leaves under drought conditions and increase the antioxidant capacity of the leaves, thereby reducing the adverse effects of drought, promoting the growth of P. purpureum, and effectively improving the drought resistance of P. purpureum.

Cloning and functional identification of setaria italica somatic embryogenesis receptor-like kinase1 gene (SiSERK1)

Plant somatic embryogenesis receptor-like kinases (SERK), members of leucine-rich repeat receptor-like kinases (LRR-RLKs) subfamily, are widely involved in plant growth, development and innate immunity. In this study, the setaria italica somatic embryogenesis receptor-like kinase1 gene (SiSERK1) was cloned by gateway technology, and transferred into a brasssinosteroid (BR) receptor mutant of Arabidopsis thaliana WS2 (bri1-5). After BL treatment, the transgenic plants could partially restore the phenotype of bri1-5. After Pst DC3000 treatment, the CFU value of SiSERK1 overexpression plant pathogen was between WS2 and bri1-5. Stomatal opening and plant height were also between them. Therefore, it is speculated that SiSERK1 gene is involved in BR signaling pathway and can improve the resistance of bri1-5 to Pst DC3000 through SA and NHP mediated systemic acquired resistance (SAR).