BcGR1.1, a Cytoplasmic Localized Glutathione Reductase, Enhanced Tolerance to Copper Stress in Arabidopsis thaliana

Effects of copper, and aluminium in ionic, and nanoparticulate form on growth rate and gene expression of Setaria italica seedlings

This study aims to determine the effects of copper, copper oxide nanoparticles, aluminium, and aluminium oxide nanoparticles on the growth rate and expression of ACT-1, CDPK, LIP, NFC, P5CR, P5CS, GR, and SiZIP1 genes in five days old seedling of Setaria italica ssp. maxima, cultivated in hydroponic culture. Depending on their concentration (ranging from 0.1 to 1.8 mg L-1), all tested substances had both stimulating and inhibiting effects on the growth rate of the seedlings. Copper and copper oxide-NPs had generally a stimulating effect whereas aluminium and aluminium oxide-NPs at first had a positive effect but in higher concentrations they inhibited the growth. Treating the seedlings with 0.4 mg L-1 of each tested toxicant was mostly stimulating to the expression of the genes and reduced the differences between the transcript levels of the coleoptiles and roots. Increasing concentrations of the tested substances had both stimulating and inhibiting effects on the expression levels of the genes. The highest expression levels were usually noted at concentrations between 0.4 and 1.0 mg/L of each metal and metal nanoparticle, except for SiZIP1, which had the highest transcript amount at 1.6 mg L-1 of Cu2+ and at 0.1-0.8 mg L-1 of CuO-NPs, and LIP and GR from the seedling treated with Al2O3-NPs at concentrations of 0.1 and 1.6 mg L-1, respectively.

Overexpression of Wheat Selenium-Binding Protein Gene TaSBP-A Enhances Plant Growth and Grain Selenium Accumulation under Spraying Sodium Selenite

Selenium (Se) is an essential trace element for humans. Low concentrations of Se can promote plant growth and development. Enhancing grain yield and crop Se content is significant, as major food crops generally have low Se content. Studies have shown that Se biofortification can significantly increase Se content in plant tissues. In this study, the genetic transformation of wheat was conducted to evaluate the agronomic traits of non-transgenic control and transgenic wheat before and after Se application. Se content, speciation, and transfer coefficients in wheat grains were detected. Molecular docking simulations and transcriptome data were utilized to explore the effects of selenium-binding protein-A TaSBP-A on wheat growth and grain Se accumulation and transport. The results showed that TaSBP-A gene overexpression significantly increased plant height (by 18.50%), number of spikelets (by 11.74%), and number of grains in a spike (by 35.66%) in wheat. Under normal growth conditions, Se content in transgenic wheat grains did not change significantly, but after applying sodium selenite, Se content in transgenic wheat grains significantly increased. Analysis of Se speciation revealed that organic forms of selenomethionine (SeMet) and selenocysteine (SeCys) predominated in both W48 and transgenic wheat grains. Moreover, TaSBP-A significantly increased the transfer coefficients of Se from solution to roots and from flag leaves to grains. Additionally, it was found that with the increase in TaSBP-A gene overexpression levels in transgenic wheat, the transfer coefficient of Se from flag leaves to grains also increased.

The ascorbate-glutathione cycle coming of age

Concepts regarding the operation of the ascorbate-glutathione cycle and the associated water/water cycle in the processing of metabolically generated hydrogen peroxide and other forms of reactive oxygen species (ROS) are well established in the literature. However, our knowledge of the functions of these cycles and their component enzymes continues to grow and evolve. Recent insights include participation in the intrinsic environmental and developmental signalling pathways that regulate plant growth, development, and defence. In addition to ROS processing, the enzymes of the two cycles not only support the functions of ascorbate and glutathione, they also have 'moonlighting' functions. They are subject to post-translational modifications and have an extensive interactome, particularly with other signalling proteins. In this assessment of current knowledge, we highlight the central position of the ascorbate-glutathione cycle in the network of cellular redox systems that underpin the energy-sensitive communication within the different cellular compartments and integrate plant signalling pathways.

SbMYC2 mediates jasmonic acid signaling to improve drought tolerance via directly activating SbGR1 in sorghum

KEY MESSAGE

SbMYC2 functions as a key regulator under JA signaling in enhancing drought tolerance of sorghum through direct activating SbGR1. Drought stress is one of the major threats to crop yield. In response to drought stress, functions of basic helix-loop-helix (bHLH) transcription factors (TFs) have been reported in Arabidopsis and rice, but little is known for sorghum. Here, we characterized the function of SbMYC2, a bHLH TF in sorghum, and found that SbMYC2 responded most significantly to PEG-simulated drought stress and JA treatments. Overexpression of SbMYC2 significantly enhanced drought tolerance in Arabidopsis, rice and sorghum. In addition, it reduced reactive oxygen species (ROS) accumulation and increased chlorophyll content in sorghum leaves. While silencing SbMYC2 by virus-induced gene silencing (VIGS) resulted in compromised drought tolerance of sorghum seedlings. Moreover, SbMYC2 can directly activate the expression of GLUTATHIONE-DISULFIDE REDUCTASE gene SbGR1. SbGR1 silencing led to significantly weakened drought tolerance of sorghum, and higher ROS accumulation and lower chlorophyll content in sorghum leaves were detected. In addition, SbMYC2 can interact with SbJAZs, suppressors of JA signaling, and thus can mediate JA signaling to activate SbGR1, thereby regulating sorghum's tolerance to drought stress. Overall, our findings demonstrate that bHLH TF SbMYC2 plays an important role in sorghum's response to drought stress, thus providing one theoretical basis for genetic enhancement of sorghum and even rice.

BcMYB111 Responds to BcCBF2 and Induces Flavonol Biosynthesis to Enhance Tolerance under Cold Stress in Non-Heading Chinese Cabbage

Flavonols have been shown to respond to a variety of abiotic stresses in plants, including cold stress. Higher total flavonoid content was found in non-heading Chinese cabbage (NHCC, Brassica campestris (syn. Brassica rapa) ssp. chinensis) after cold stress. A non-targeted metabolome analysis showed a significant increase in flavonol content, including that of quercetin and kaempferol. Here, we found that an R2R3-MYB transcription factor, BcMYB111, may play a role in this process. BcMYB111 was up-regulated in response to cold treatment, with an accompanying accumulation of flavonols. Then, it was found that BcMYB111 could regulate the synthesis of flavonols by directly binding to the promoters of BcF3H and BcFLS1. In the transgenic hairy roots of NHCC or stable transgenic Arabidopsis, overexpression of BcMYB111 increased flavonol synthesis and accumulation, while these were reduced in virus-induced gene silencing lines in NHCC. After cold stress, the higher proline content and lower malondialdehyde (MDA) content showed that there was less damage in transgenic Arabidopsis than in the wild-type (WT). The BcMYB111 transgenic lines performed better in terms of antioxidant capacity because of their lower H₂O₂ content and higher superoxide dismutase (SOD) and peroxidase (POD) enzyme activities. In addition, a key cold signaling gene, BcCBF2, could specifically bind to the DRE element and activate the expression of BcMYB111 in vitro and in vivo. The results suggested that BcMYB111 played a positive role in enhancing the flavonol synthesis and cold tolerance of NHCC. Taken together, these findings reveal that cold stress induces the accumulation of flavonols to increase tolerance via the pathway of BcCBF2-BcMYB111-BcF3H/BcFLS1 in NHCC.

Lead exposure dose-dependently affects oxidative stress, AsA-GSH, photosynthesis, and mineral content in pakchoi (Brassica chinensis L.)

Lead (Pb) is a heavy metal pollutant and negatively affects agriculture and ecosystems. Pb can cause oxidative stress and abnormal plant growth. The ascorbic acid-glutathione (AsA-GSH) cycle mainly exists in chloroplasts and resists oxidative stress, scavenges reactive oxygen radicals, and maintains normal photosynthesis. However, the dosage related effects of Pb on pakchoi photosynthesis, via oxidative stress and the AsA-GSH system, remains unclear. In this study, various Pb dosage stress models were tested (low: 300 mg/kg; medium: 600 mg/kg; high: 900 mg/kg). Pb stress induced a dose-dependent increase in Pb content in pakchoi leaves (P < 0.05). Principal component analysis showed that Se, B, and Pb were significantly and negatively correlated. Pb stress also increased MDA content and decreased antioxidant enzymes SOD, GSH-Px, and T-AOC activities (P < 0.05). We also found that Vc content, as well as the GSH/GSSG ratio, decreased. Additionally, Pb stress destroyed chloroplast structure, decreased photosynthesis indicators Pn, Tr, Gs, Ci and VPD, and attenuated Fv/Fm and Fv/Fo (P < 0.05). In the high-dose group, the contents of chlorophyll a, chlorophyll b, and carotenoids decreased significantly, while the expression of chloroplast development genes (GLK, GLN2) decreased (P < 0.05). Our data suggest that Pb stress leads to dosage-dependent, aberrant photosynthesis by inhibiting the AsA-GSH system in pakchoi. This study expands the Pb toxicology research field and provides indications for screening antagonists.

Genome-Wide Analysis and Expression Profiling of Glutathione Reductase Gene Family in Oat (Avena sativa) Indicate Their Responses to Abiotic Stress during Seed Imbibition

Abiotic stress disturbs plant cellular redox homeostasis, inhibiting seed germination and plant growth. This is a crucial limitation to crop yield. Glutathione reductase (GR) is an important component of the ascorbate-glutathione (AsA-GSH) cycle which is involved in multiple plant metabolic processes. In the present study, GRs in A. sativa (AsGRs) were selected to explore their molecular characterization, phylogenetic relationship, and RNA expression changes during seed imbibition under abiotic stress. Seven AsGR genes were identified and mapped on six chromosomes of A, C, and D subgenomes. Phylogenetic analysis and subcellular localization of AsGR proteins divided them into two sub-families, AsGR1 and AsGR2, which were predicted to be mainly located in cytoplasm, mitochondrion, and chloroplast. Cis-elements relevant to stress and hormone responses are distributed in promoter regions of AsGRs. Tissue-specific expression profiling showed that AsGR1 genes were highly expressed in roots, leaves, and seeds, while AsGR2 genes were highly expressed in leaves and seeds. Both AsGR1 and AsGR2 genes showed a decreasing-increasing expression trend during seed germination under non-stress conditions. In addition, their responses to drought, salt, cold, copper, H₂O₂, and ageing treatments were quite different during seed imbibition. Among the seven AsGR genes, AsGR1-A, AsGR1-C, AsGR2-A, and AsGR2-D responded more significantly, especially under drought, ageing, and H₂O₂ stress. This study has laid the ground for the functional characterization of GR and the improvement of oat stress tolerance and seed vigor.

Selenium Uptake, Transport, Metabolism, Reutilization, and Biofortification in Rice

Selenium (Se) is an essential trace element for humans and other animals. The human body mainly acquires Se from plant foods, especially cereal grains. Rice is the staple food for more than half of the world's population. Increasing the Se concentration of rice grains can increase the average human dietary Se intake. This review summarizes recent advances in the molecular mechanisms of Se uptake, transport, subcellular distribution, retranslocation, volatilization, and Se-containing protein degradation in plants, especially rice. The strategies for improving Se concentration in rice grains by increasing Se accumulation, reducing Se volatilization, and optimizing Se form were proposed, which provide new insight into Se biofortification in rice by improving the utilization efficiency of Se.