Transgenic tobacco plants expressing atzA exhibit resistance and strong ability to degrade atrazine

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

Bacterial catabolism of s-triazine herbicides: biochemistry, evolution and application

The synthetic s-triazines are abundant, nitrogen-rich, heteroaromatic compounds used in a multitude of applications including, herbicides, plastics and polymers, and explosives. Their presence in the environment has led to the evolution of bacterial catabolic pathways in bacteria that allow use of these anthropogenic chemicals as a nitrogen source that supports growth. Herbicidal s-triazines have been used since the mid-twentieth century and are among the most heavily used herbicides in the world, despite being withdrawn from use in some areas due to concern about their safety and environmental impact. Bacterial catabolism of the herbicidal s-triazines has been studied extensively. Pseudomonas sp. strain ADP, which was isolated more than thirty years after the introduction of the s-triazine herbicides, has been the model system for most of these studies; however, several alternative catabolic pathways have also been identified. Over the last five years, considerable detail about the molecular mode of action of the s-triazine catabolic enzymes has been uncovered through acquisition of their atomic structures. These structural studies have also revealed insights into the evolutionary origins of this newly acquired metabolic capability. In addition, s-triazine-catabolizing bacteria and enzymes have been used in a range of applications, including bioremediation of herbicides and cyanuric acid, introducing metabolic resistance to plants, and as a novel selectable marker in fermentation organisms. In this review, we cover the discovery and characterization of bacterial strains, metabolic pathways and enzymes that catabolize the s-triazines. We also consider the evolution of these new enzymes and pathways and discuss the practical applications that have been considered for these bacteria and enzymes. One Sentence Summary: A detailed understanding of bacterial herbicide catabolic enzymes and pathways offer new evolutionary insights and novel applied tools.

Degrading and Phytoextracting Atrazine Residues in Rice (Oryza sativa) and Growth Media Intensified by a Phase II Mechanism Modulator

Atrazine (ATZ) residue in farmland is one of the environmental contaminants seriously affecting crop production and food safety. Understanding the regulatory mechanism for ATZ metabolism and degradation in plants is important to help reduce ATZ potential toxicity to both plants and human health. Here, we report our newly developed engineered rice overexpressing a novel Phase II metabolic enzyme glycosyltransfearse1 (ARGT1) responsible for transformation of ATZ residues in rice. Our results showed that transformed lines, when exposed to environmentally realistic ATZ concentration (0.2-0.8 mg/L), displayed significantly high tolerance, with 8-27% biomass and 36-56% chlorophyll content higher, but 37-69% plasma membrane injury lower than untransformed lines. Such results were well confirmed by ARGT1 expression in Arabidopsis. ARGT1-transformed rice took up 1.6-2.7 fold ATZ from its growth medium compared to its wild type (WT) and accumulated ATZ 10%-43% less than that of WT. A long-term study also showed that ATZ in the grains of ARGT1-transformed rice was reduced by 30-40% compared to WT. The ATZ-degraded products were characterized by UPLC/Q-TOF-MS/MS. More ATZ metabolites and conjugates accumulated in ARGT1-transformed rice than in WT. Eight ATZ metabolites for Phase I reaction and 10 conjugates for Phase II reaction in rice were identified, with three ATZ-glycosylated conjugates that have never been reported before. These results indicate that ARGT1 expression can facilitate uptake of ATZ from environment and metabolism in rice plants.

Evaluation of the agronomic performance of atrazine-tolerant transgenic japonica rice parental lines for utilization in hybrid seed production

Currently, the purity of hybrid seed is a crucial limiting factor when developing hybrid japonica rice (Oryza sativa L.). To chemically control hybrid seed purity, we transferred an improved atrazine chlorohydrolase gene (atzA) from Pseudomonas ADP into hybrid japonica parental lines (two maintainers, one restorer), and Nipponbare, by using Agrobacterium-mediated transformation. We subsequently selected several transgenic lines from each genotype by using PCR, RT-PCR, and germination analysis. In the presence of the investigated atrazine concentrations, particularly 150 µM atrazine, almost all of the transgenic lines produced significantly larger seedlings, with similar or higher germination percentages, than did the respective controls. Although the seedlings of transgenic lines were taller and gained more root biomass compared to the respective control plants, their growth was nevertheless inhibited by atrazine treatment compared to that without treatment. When grown in soil containing 2 mg/kg or 5 mg/kg atrazine, the transgenic lines were taller, and had higher total chlorophyll contents than did the respective controls; moreover, three of the strongest transgenic lines completely recovered after 45 days of growth. After treatment with 2 mg/kg or 5 mg/kg of atrazine, the atrazine residue remaining in the soil was 2.9–7.0% or 0.8–8.7% respectively, for transgenic lines, and 44.0–59.2% or 28.1–30.8%, respectively, for control plants. Spraying plants at the vegetative growth stage with 0.15% atrazine effectively killed control plants, but not transgenic lines. Our results indicate that transgenic atzA rice plants show tolerance to atrazine, and may be used as parental lines in future hybrid seed production.