Transcriptomic and metabolomic analysis provides insight into imazethapyr toxicity to non-target plants.

Imazethapyr is a widely used imidazolinone herbicide worldwide, and its potential adverse effects on non-target plants have raised concerns. Understanding the mechanisms of imazethapyr phytotoxicity is crucial for its agro-ecological risk assessment. Here, the comprehensive molecular responses and metabolic alterations of Arabidopsis in response to imazethapyr were investigated. Our results showed that root exposure to imazethapyr inhibited shoot growth, reduced chlorophyll contents, induced photoinhibition and decreased photosynthetic activity. By non-target metabolomic analysis, we identified 75 metabolites that were significantly changed after imazethapyr exposure, and they are mainly enriched in carbohydrate, lipid and amino acid metabolism. Transcriptomic analysis confirmed that imazethapyr significantly downregulated the genes involved in photosynthetic electron transport and the carbon cycle. In detail, 48 genes in the photosynthetic lightreaction and 11 genes in Calvin cycle were downregulated. Additionally, the downregulation of genes related to electron transport in mitochondria provides strong evidence for imazethapyr inhibiting photosynthetic carbon fixation and cellular energy metabolism as one of mechanisms of toxicity. These results revealed the molecular and metabolic basis of imazethapyr toxicity on non-target plants, contributing to environmental risk assessment and mitigate negative impact of imazethapyr residues in agricultural soils.

Effects of SMOF on soil properties, root-zone microbial community structure, metabolites, and maize (Zea mays L.) response on a reclaimed barren mountainous land.

Introduction: Maize is the largest crop produced in China. With the growing population and the rapid development of urbanization and industrialization, maize has been recently cultivated in reclaimed barren mountainous lands in Zhejiang Province, China. However, the soil is usually not suitable for cultivation because of its low pH and poor nutrient conditions. To improve soil quality for crop growth, various fertilizers, including inorganic, organic, and microbial fertilizers, were used in the field. Among them, organic fertilizer-based sheep manure greatly improved the soil quality and has been widely adopted in reclaimed barren mountainous lands. But the mechanism of action was not well clear. Methods: The field experiment (SMOF, COF, CCF and the control) was carried out on a reclaimed barren mountainous land in Dayang Village, Hangzhou City, Zhejiang Province, China. To systematically evaluate the effect of SMOF on reclaimed barren mountainous lands, soil properties, the root-zone microbial community structure, metabolites, and maize response were investigated. Results: Compared with the control, SMOF could not significantly affect the soil pH but caused 46.10%, 28.28%, 101.94%, 56.35%, 79.07%, and 76.07% increases in the OMC, total N, available P, available K, MBC, and MBN, respectively. Based on 16S amplicon sequencing of soil bacteria, compared with the control, SMOF caused a 11.06-334.85% increase in the RA of Ohtaekwangia, Sphingomonas, unclassified_Sphingomonadaceae, and Saccharibacteria and a 11.91-38.60% reduction in the RA of Spartobacteria, Gemmatimonas, Gp4, Flavisolibacter, Subdivision3, Gp6, and unclassified_Betaproteobacteria, respectively. Moreover, based on ITS amplicon sequencing of soil fungi, SMOF also caused a 42.52-330.86% increase in the RA of Podospora, Clitopilus, Ascobolus, Mortierella, and Sordaria and a 20.98-64.46% reduction in the RA of Knufia, Fusarium, Verticillium, and Gibberella, respectively, compared with the control. RDA of microbial communities and soil properties revealed that the main variables of bacterial and fungal communities included available K, OMC, available P, MBN, and available K, pH, and MBC, respectively. In addition, LC-MS analysis indicated that 15 significant DEMs belonged to benzenoids, lipids, organoheterocyclic compounds, organic acids, phenylpropanoids, polyketides, and organic nitrogen compounds in SMOF and the control group, among which four DEMs were significantly correlated with two genera of bacteria and 10 DEMs were significantly correlated with five genera of fungi. The results revealed complicated interactions between microbes and DEMs in the soil of the maize root zone. Furthermore, the results of field experiments demonstrated that SMOF could cause a significant increase in maize ears and plant biomass. Conclusions: Overall, the results of this study showed that the application of SMOF not only significantly modified the physical, chemical, and biological properties of reclaimed barren mountainous land but also promoted maize growth. SMOF can be used as a good amendment for maize production in reclaimed barren mountainous lands.

Synergistic interplay between ABA-generating bacteria and biochar in the reduction of heavy metal accumulation in radish, pakchoi, and tomato.

Heavy metal (HM) contamination is an environmental concern that threatens the agricultural product safety and human health. To address this concern, we developed a novel strategy involving the synergistic application of Azospirillum brasilense, a growth-promoting rhizobacterium which produces abscisic acid (ABA), and biochar to minimize HM accumulation in the edible parts of vegetable crops. Compared to A. brasilense or biochar alone, the concentrations of Cd, Ni, Pb, and Zn in radish (Raphanus sativus L.), pakchoi (Brassica chinensis L.), and tomato (Lycopersicon esculentum L.) decreased by 18-63% and 14-56%, respectively. Additionally, the synergistic treatment led to a 14-63% decrease in the bioconcentration factor. The biomass of the edible parts of the three crops increased by 65-278% after synergistic treatment, surpassing the effects of single treatments. Furthermore, the synergistic application enhanced the SPAD values by 1-45% compared to single treatments. The MDA concentrations in stressed plants decreased by 16-39% with the bacteria-biochar co-treatment compared to single treatments. Co-treatment also resulted in increased soluble protein and sugar concentrations by 8-174%, and improvements in flavonoids, total phenols, ascorbic acid, and DPPH levels by 2-50%. Pearson correlation analysis and structural equation modeling revealed that the synergistic effect was attributed to the enhanced growth of A. brasilense facilitated by biochar and the improved availability of HMs in soils. Notably, although ABA concentrations were not as high as those achieved with A. brasilense alone, they were maintained at relatively high levels. Overall, the synergistic application of A. brasilense-biochar might have remarkable potential for reducing the accumulation of HMs while promoting growth and improving nutritional and antioxidant qualities in tuberous, leafy, and fruit crops.

Enantioselectivity in the toxicological effects of chiral pesticides: A review.

As a special category of pesticides, chiral pesticides have increased the difficulty in investigating pesticide toxicity. Based on their usage, chiral pesticides can be divided into insecticides, herbicides, and fungicides. Over the past decades, great efforts have been made on elucidating their toxicological effects. However, no literature has reviewed the enantioselective toxicity of chiral pesticides since 2014. In recent years, more chiral pesticides have been registered for application. As such, huge research progresses have been achieved in enantioselective toxicity of chiral pesticides. Generally, more researches have remedied the knowledge gap in toxicological effects of old and new chiral pesticides. And the toxicological endpoints being evaluated have become more specific rather than centering on basic toxicity and target organisms. Besides, the underlying mechanisms accounting for the enantioselectivity in toxicological effects of chiral pesticides have been discussed as well. All in all, this review provides the critical knowledge for risk assessments, and help to drive the green-technology of single- or enriched-enantiomer pesticides and formulation of relevant laws and regulations.

Graphene oxide decreases the abundance of nitrogen cycling microbes and slows nitrogen transformation in soils.

Graphene oxide (GO) has been widely used in many applications due to its excellent properties. Given the extensive production and use of this nanomaterial, its release into the environment is inevitable. However, little is known about the effects of GO on microbial nitrogen transformation and the related processes after GO enters the soil environment. The present study showed that GO significantly reduced soil microbial biomass and caused a decline in microbial diversity after the soils were subjected to various GO concentrations (10, 100, and 1000 mg kg-1) for 4 months. Among them, the abundances of nitrogen transformation related bacteria such as Firmicutes, Nitrospirota, Proteobacteria, Planctomycetota, and Cyanobacteria were significantly decreased with GO incubation. Among the enzymes that are related to nitrogen transformation, nitrate reductase was the most sensitive even at low concentrations of GO, followed by ammonia monooxygenase and urease, which were reduced by 13-31%, 5-26%, and 9-19% respectively, than those of the control. We found that high concentrations of GO significantly increased the retention of soil urea by 32-59%, and the contents of ammonium and nitrate were 22-28% and 55-69% lower compared to those of the control, respectively. Moreover, the response of most of the indicators in the above process to multilayer GO was more significant than that to single layer GO. Overall, this study provides new insights into the comprehensive understanding of GO's impacts on the soil nitrogen cycle.

Identification and Characterization of a Novel Protein Disulfide Isomerase Gene (MgPDI2) from Meloidogyne graminicola.

Protein disulfide isomerase (PDI) is a multifunctional enzyme that catalyzes rate-limiting reactions such as disulfide bond formation, isomerization, and reduction. There is some evidence that indicates that PDI is also involved in host-pathogen interactions in plants. In this study, we show that the rice root-knot nematode, Meloidogyne graminicola, has evolved a secreted effector, MgPDI2, which is expressed in the subventral esophageal glands and up-regulated during the early parasitic stage of M. graminicola. Purified recombinant MgPDI2 functions as an insulin disulfide reductase and protects plasmid DNA from nicking. As an effector, MgPDI2 contributes to nematode parasitism. Silencing of MgPDI2 by RNA interference in the pre-parasitic second-stage juveniles (J2s) reduced M. graminicola multiplication and also increased M. graminicola mortality under H2O2 stress. In addition, an Agrobacterium-mediated transient expression assay found that MgPDI2 caused noticeable cell death in Nicotiana benthamiana. An intact C-terminal region containing the first catalytic domain (a) with an active motif (Cys-Gly-His-Cys, CGHC) and the two non-active domains (b and b') is required for cell death induction in N. benthamiana. This research may provide a promising target for the development of new strategies to combat M. graminicola infections.

Meloidogyne graminicola protein disulfide isomerase may be a nematode effector and is involved in protection against oxidative damage.

The rice root-knot nematode, Meloidogyne graminicola, is a serious pest in most rice-growing countries. Usually, nematodes employ antioxidants to counteract the harm of reactive oxygen species (ROS) and facilitate their infection. Here the gene encoding M. graminicola protein disulphide isomerase (MgPDI) was identified. The deduced protein is highly conserved in the putative active-site Cys-Gly-His-Cys. In situ hybridization showed that MgPDI was specifically localized within esophageal glands of pre-parasitic second stage juveniles (J2s). MgPDI was significantly up-regulated in the late parasitic J2s. Characterization of the recombinant protein showed that the purified MgPDI exhibited similar activities to other oxidases/isomerases such as the refolding of the scrambled RNase and insulin disulfide reductase and the protection of plasmid DNA and living cells from ROS damage. In addition, silencing of MgPDI by RNA interference in the pre-parasitic J2s lowered their multiplication factor. MgPDI expression was up-regulated in the presence of exogenous H2O2, whereas MgPDI silencing resulted in an increase in mortality under H2O2 stress. MgPDI is localized in the apoplast when transient expression in Nicotiana benthamiana leaves. The results indicated that MgPDI plays important roles in the reproduction and pathogenicity of M. graminicola and it also contributes to protecting nematodes from exogenous H2O2 stress.

Description and Distribution of Three Criconematid Nematodes from Hangzhou, Zhejiang Province, China.

Populations of Criconemoides parvus , Discocriconemella hengsungica , and Discocriconemella limitanea , isolated in Hangzhou, China from the rhizosphere soil of woody perennials were characterized morphologically and molecularly. The morphometric data of the Chinese populations were compared with populations from other regions of the world. DNA barcoding with the mitochondrial COI gene confirmed conspecificity of Chinese and Costa Rican populations of D. limitanea . Phylogenetic assessment using a near full-length 18S ribosomal DNA sequence provided weak support for a grouping of Criconemoides parvus from China and C. annulatus from western North America. The phylogenetic position of D. hengsungica from China and an unknown species of Discocriconemella from Thailand relative to D. limitanea suggests that the genus Discocriconemella is not monophyletic. The study provides the first record of D. hengsungica in China and confirms the presence of C. parvus previously reported from China. Biogeographic implications of these nematode distributions are discussed.