The complete degradation of 1,2-dichloroethane in Escherichia coli by metabolic engineering.

1,2-Dichloroethane (1,2-DCA), a widely utilized chemical intermediate and organic solvent in industry, frequently enters the environment due to accidental leaks and mishandling during application processes. Thus, the in-situ remediation of contaminated sites has become increasingly urgent. However, traditional remediation methods are inefficient and costly, while bioremediation presents a green, efficient, and non-secondary polluting alternative. In this study, an engineered strain capable of completely degrading 1,2-DCA was constructed. We introduced six exogenous genes of the 1,2-DCA degradation pathway into E. coli and confirmed their normal transcription and efficient expression in this engineered strain through qRT-PCR and proteomics. The degradation experiments showed that the strain completely degraded 2 mM 1,2-DCA within 12 h. Furthermore, the results of isotope tracing verified that the final degradation product, malic acid, entered the tricarboxylic acid cycle (TCA) of E. coli and was ultimately fully metabolized. Also, morphological changes in the engineered strain and control strain exposed to 1,2-DCA were observed under SEM, and the results revealed that the engineered strain is more tolerant to 1,2-DCA than the control strain. In conclusion, this study paved a new way for humanity to deal with the increasingly complex environmental challenges.

Toward breeding pigmented rice balancing nutrition and yield.

A recent study by Sedeek et al. provides multiomic resources that illustrate the genetic diversity, metabolites, elemental composition, and the possibility of agronomic trait improvement, through genome-editing technology, for nutrient-rich pigmented rice. This will guide future rice breeding programs for balancing optimal agronomic traits and excellent nutritional quality.

Creation of Environmentally Friendly Super "Dinitrotoluene Scavenger" Plants.

Pervasive environmental contamination due to the uncontrolled dispersal of 2,4-dinitrotoluene (2,4-DNT) represents a substantial global health risk, demanding urgent intervention for the removal of this detrimental compound from affected sites and the promotion of ecological restoration. Conventional methodologies, however, are energy-intensive, susceptible to secondary pollution, and may inadvertently increase carbon emissions. In this study, a 2,4-DNT degradation module is designed, assembled, and validated in rice plants. Consequently, the modified rice plants acquire the ability to counteract the phytotoxicity of 2,4-DNT. The most significant finding of this study is that these modified rice plants can completely degrade 2,4-DNT into innocuous substances and subsequently introduce them into the tricarboxylic acid cycle. Further, research reveals that the modified rice plants enable the rapid phytoremediation of 2,4-DNT-contaminated soil. This innovative, eco-friendly phytoremediation approach for dinitrotoluene-contaminated soil and water demonstrates significant potential across diverse regions, substantially contributing to carbon neutrality and sustainable development objectives by repurposing carbon and energy from organic contaminants.

Metabolic engineering of Escherichia coli for 2,4-dinitrotoluene degradation.

2,4-Dinitrotoluene (2,4-DNT) as a common industrial waste has been massively discharged into the environment with industrial wastewater. Due to its refractory degradation, high toxicity, and bioaccumulation, 2,4-DNT pollution has become increasingly serious. Compared with the currently available physical and chemical methods, in situ bioremediation is considered as an economical and environmentally friendly approach to remove toxic compounds from contaminated environment. In this study, we relocated a complete degradation pathway of 2,4-DNT into Escherichia coli to degrade 2,4-DNT completely. Eight genes from Burkholderia sp. strain were re-synthesized by PCR-based two-step DNA synthesis method and introduced into E. coli. Degradation experiments revealed that the transformant was able to degrade 2,4-DNT completely in 12 h when the 2,4-DNT concentration reached 3 mM. The organic acids in the tricarboxylic acid cycle were detected to prove the degradation of 2,4-DNT through the artificial degradation pathway. The results proved that 2,4-DNT could be completely degraded by the engineered bacteria. In this study, the complete degradation pathway of 2,4-DNT was constructed in E. coli for the first time using synthetic biology techniques. This research provides theoretical and experimental bases for the actual treatment of 2,4-DNT, and lays a technical foundation for the bioremediation of organic pollutants.

Complete biodegradation of the oldest organic herbicide 2,4-Dichlorophenoxyacetic acid by engineering Escherichia coli.

After nearly 80 years of extensive application, the oldest organic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) has caused many problems of environmental pollution and ecological deterioration. Bioremediation is an ideal method for pollutant treatment. However, difficult screening and preparation of efficient degradation bacteria have largely hindered its application in 2,4-D remediation. We have created a novel engineering Escherichia coli with a reconstructed complete degradation pathway of 2,4-D to solve the problem of screening highly efficient degradation bacteria in this study. The results of fluorescence quantitative PCR demonstrated that all nine genes in the degradation pathway were successfully expressed in the engineered strain. The engineered strains can quickly and completely degrade 0.5 mM 2, 4-D within 6 h. Inspiring, the engineered strains grew with 2,4-D as the sole carbon source. By using the isotope tracing method, the metabolites of 2,4-D were found incorporated into the tricarboxylic acid cycle in the engineering strain. Scanning electron microscopy showed that 2,4-D had less damage on the engineered bacteria than the wild-type strain. Engineered strain can also rapidly and completely remedy 2,4-D pollution in natural water and soil. Assembling the metabolic pathways of pollutants through synthetic biology was an effective method to create pollutant-degrading bacteria for bioremediation.

Nucleotide polymorphisms of the maize ZmFWL7 gene and their association with ear-related traits.

Plant fw2.2-like (FWL) genes, encoding proteins harboring a placenta-specific eight domain, have been suggested to control fruit and grain size through regulating cell division, differentiation, and expansion. Here, we re-sequenced the nucleotide sequences of the maize ZmFWL7 gene, a member of the FWL family, in 256 elite maize inbred lines, and the associations of nucleotide polymorphisms in this locus with 11 ear-related traits were further detected. A total of 175 variants, including 159 SNPs and 16 InDels, were identified in the ZmFWL7 locus. Although the promoter and downstream regions showed higher nucleotide polymorphism, the coding region also possessed 61 SNPs and 6 InDels. Eleven polymorphic sites in the ZmFWL7 locus were found to be significantly associated with eight ear-related traits. Among them, two nonsynonymous SNPs (SNP2370 and SNP2898) showed significant association with hundred kernel weight (HKW), and contributed to 7.11% and 8.62% of the phenotypic variations, respectively. In addition, the SNP2898 was associated with kernel width (KW), and contributed to 7.57% of the phenotypic variations. Notably, the elite allele T of SNP2370 was absent in teosintes and landraces, while its frequency in inbred lines was increased to 12.89%. By contrast, the frequency of the elite allele A of SNP2898 was 3.12% in teosintes, and it was raised to 12.68% and 19.92% in landraces and inbred lines, respectively. Neutral tests show that this locus wasn't artificially chosen during the process of domestication and genetic improvement. Our results revealed that the elite allelic variants in ZmFWL7 might possess potential for the genetic improvement of maize ear-related traits.

The plant streptolysin S (SLS)-associated gene B confers nitroaromatic tolerance and detoxification.

Nitroaromatic compounds, as the important chemical feedstock, have caused widespread environmental contaminations, and exhibited high toxicity and mutagenic activity to nearly all living organisms. The clean-up of nitroaromatic-contaminated soil and water has long been a major international concern. Here, we uncovered the role of a novel nitroreductase family gene, streptolysin S (SLS)-associated gene B (SagB), in enhancing nitroaromatic tolerance and detoxification of plants, and its potential application in phytoremediation of nitroaromatic contaminations. The expression of both the Arabidopsis and rice SagB genes is significantly induced by multiple hazardous nitroaromatic substances, including explosive pollutant 2,4,6-trinitrotoluene (TNT), natural compound 1-nitropyrene (1-NP) and herbicide pendimethalin (Pen). In vitro and in vivo evidences revealed that plant SagBs possess activities in degradation of these nitroaromatic substances. Arabidopsis and rice transgenic assays suggested that plant SagB genes increase tolerance and detoxification of nitroaromatic through facilitating its transformation to the amino derivative. More importantly, overexpression of plant SagBs increase their ability in TNT uptake, and remove more TNT from the growth culture. Our findings shed novel insights into a plant endogenous nitroreductase-mediated nitroaromatic tolerance and detoxification, and provide a new gene target for phytoremediation of nitroaromatic-contaminated environments.

OsCOMT, encoding a caffeic acid O-methyltransferase in melatonin biosynthesis, increases rice grain yield through dual regulation of leaf senescence and vascular development.

Melatonin, a natural phytohormone in plants, plays multiple critical roles in plant growth and stress responses. Although melatonin biosynthesis-related genes have been suggested to possess diverse biological functions, their roles and functional mechanisms in regulating rice grain yield remain largely unexplored. Here, we uncovered the roles of a caffeic acid O-methyltransferase (OsCOMT) gene in mediating rice grain yield through dual regulation of leaf senescence and vascular development. In vitro and in vivo evidence revealed that OsCOMT is involved in melatonin biosynthesis. Transgenic assays suggested that OsCOMT significantly delays leaf senescence at the grain filling stage by inhibiting degradation of chlorophyll and chloroplast, which, in turn, improves photosynthesis efficiency. In addition, the number and size of vascular bundles in the culms and leaves were significantly increased in the OsCOMT-overexpressing plants, while decreased in the knockout plants, suggesting that OsCOMT plays a positive role in vascular development of rice. Further evidence indicated that OsCOMT-mediated vascular development might owe to the crosstalk between melatonin and cytokinin. More importantly, we found that OsCOMT is a positive regulator of grain yield, and overexpression of OsCOMT increase grain yield per plant even in a high-yield variety background, suggesting that OsCOMT can be used as an important target for enhancing rice yield. Our findings shed novel insights into melatonin-mediated leaf senescence and vascular development and provide a possible strategy for genetic improvement of rice grain yield.

Nucleotide Diversity of the Maize ZmCNR13 Gene and Association With Ear Traits.

The maize (Zea mays L.) ZmCNR13 gene, encoding a protein of fw2.2-like (FWL) family, has been demonstrated to be involved in cell division, expansion, and differentiation. In the present study, the genomic sequences of the ZmCNR13 locus were re-sequenced in 224 inbred lines, 56 landraces and 30 teosintes, and the nucleotide polymorphism and selection signature were estimated. A total of 501 variants, including 415 SNPs and 86 Indels, were detected. Among them, 51 SNPs and 4 Indels were located in the coding regions. Although neutrality tests revealed that this locus had escaped from artificial selection during the process of maize domestication, the population of inbred lines possesses lower nucleotide diversity and decay of linkage disequilibrium. To estimate the association between sequence variants of ZmCNR13 and maize ear characteristics, a total of ten ear-related traits were obtained from the selected inbred lines. Four variants were found to be significantly associated with six ear-related traits. Among them, SNP2305, a non-synonymous mutation in exon 2, was found to be associated with ear weight, ear grain weight, ear diameter and ear row number, and explained 4.59, 4.61, 4.31, and 8.42% of the phenotypic variations, respectively. These results revealed that natural variations of ZmCNR13 might be involved in ear development and can be used in genetic improvement of maize ear-related traits.