A Critical Review of Conventional and Modern Approaches to Develop Herbicide-Resistance in Rice.

Together with rice, weeds strive for nutrients and space in farmland, resulting in reduced rice yield and quality. Planting herbicide-resistant rice varieties is one of the effective ways to control weeds. In recent years, a series of breakthroughs have been made to generate herbicide-resistant germplasm, especially the emergence of biotechnological tools such as gene editing, which provides an inherent advantage for the knock-out or knock-in of the desired genes. In order to develop herbicide-resistant rice germplasm resources, gene manipulation has been conducted to enhance the herbicide tolerance of rice varieties through the utilization of techniques such as physical and chemical mutagenesis, as well as genome editing. Based on the current research and persisting problems in rice paddy fields, research on the generation of herbicide-resistant rice still needs to explore genetic mechanisms, stacking multiple resistant genes in a single genotype, and transgene-free genome editing using the CRISPR system. Current rapidly developing gene editing technologies can be used to mutate herbicide target genes, enabling targeted genes to maintain their biological functions, and reducing the binding ability of target gene encoded proteins to corresponding herbicides, ultimately resulting in herbicide-resistant crops. In this review article, we have summarized the utilization of conventional and modern approaches to develop herbicide-resistant cultivars in rice as an effective strategy for weed control in paddy fields, and discussed the technology and research directions for creating herbicide-resistant rice in the future.

B. subtilis CNBG-PGPR-1 induces methionine to regulate ethylene pathway and ROS scavenging for improving salt tolerance of tomato.

Soil salinity severely threatens plant growth and crop yields. The utilization of PGPR is an effective strategy for enhancing plant salt tolerance, but the mechanisms involved in this process have rarely been reported. In this study, we investigated the effects of Bacillus subtilis CNBG-PGPR-1 on improving plant salt tolerance and elucidated the molecular pathways involved. The results showed that CNBG-PGPR-1 significantly improved the cellular homeostasis and photosynthetic efficiency of leaves and reduced ion toxicity and osmotic stress caused by salt in tomato. Transcriptome analysis uncovered that CNBG-PGPR-1 enhanced plant salt tolerance through the activation of complex molecular pathways, with plant hormone signal transduction playing an important role. Comparative analysis and pharmacological experiments confirmed that the ethylene pathway was closely related to the beneficial effect of CNBG-PGPR-1 on improving plant salt tolerance. Furthermore, we found that methionine, a precursor of ethylene synthesis, significantly accumulated in response to CNBG-PGPR-1 in tomato. Exogenous L-methionine largely mimicked the beneficial effects of CNBG-PGPR-1 and activated the expression of ethylene pathway-related genes, indicating CNBG-PGPR-1 induces methionine accumulation to regulate the ethylene pathway in tomato. Finally, CNBG-PGPR-1 reduced salt-induced ROS by activating ROS scavenger-encoding genes, mainly involved in GSH metabolism and POD-related genes, which were also closely linked to methionine metabolism. Overall, our studies demonstrate that CNBG-PGPR-1-induced methionine is a key regulator in enhancing plant salt tolerance through the ethylene pathway and ROS scavenging, providing a novel understanding of the mechanism by which beneficial microbes improve plant salt tolerance.

SNARE proteins VAMP721 and VAMP722 mediate the post-Golgi trafficking required for auxin-mediated development in Arabidopsis.

The plant hormone auxin controls many aspects of plant development. Membrane trafficking processes, such as secretion, endocytosis and recycling, regulate the polar localization of auxin transporters in order to establish an auxin concentration gradient. Here, we investigate the function of the Arabidopsis thaliana R-SNAREs VESICLE-ASSOCIATED MEMBRANE PROTEIN 721 (VAMP721) and VAMP722 in the post-Golgi trafficking required for proper auxin distribution and seedling growth. We show that multiple growth phenotypes, such as cotyledon development, vein patterning and lateral root growth, were defective in the double homozygous vamp721 vamp722 mutant. Abnormal auxin distribution and root patterning were also observed in the mutant seedlings. Fluorescence imaging revealed that three auxin transporters, PIN-FORMED 1 (PIN1), PIN2 and AUXIN RESISTANT 1 (AUX1), aberrantly accumulate within the cytoplasm of the double mutant, impairing the polar localization at the plasma membrane (PM). Analysis of intracellular trafficking demonstrated the involvement of VAMP721 and VAMP722 in the endocytosis of FM4-64 and the secretion and recycling of the PIN2 transporter protein to the PM, but not its trafficking to the vacuole. Furthermore, vamp721 vamp722 mutant roots display enlarged trans-Golgi network (TGN) structures, as indicated by the subcellular localization of a variety of marker proteins and the ultrastructure observed using transmission electron microscopy. Thus, our results suggest that the R-SNAREs VAMP721 and VAMP722 mediate the post-Golgi trafficking of auxin transporters to the PM from the TGN subdomains, substantially contributing to plant growth.

Identification of a linear B-cell epitope on glycoprotein (GP) 2a of porcine reproductive and respiratory syndrome virus (PRRSV).

Glycoprotein (GP) 2a was a minor structural protein of porcine reproductive and respiratory syndrome virus (PRRSV) and was one of crucial proteins for PRRSV to bind cell receptor, which indicated that there were neutralizing epitopes on GP2a. In the present work, we used mouse anti-GP2a41-208aa serum and one GP2a41-208aa specific monoclonal antibody (McAb) to identify B-cell epitopes of GP2a by peptide-based ELISA. A liner B-cell epitope F194PTPGSRPKLHDFQQ208 was identified. However, the results of virus neutralization experiment showed that the McAb could not reduce the titers of PRRSV, which indicated that the identified epitope was not the neutralizing epitope of PRRSV. While the amino acid sequence of this epitope was conserved in North American (type 2) PRRSV, which suggested that this epitope might be diagnostic potential for type 2 PRRSV strains. In conclusion, our present work identified a new epitope on GP2a and this epitope might be diagnostic potential for type 2 PRRSV strains.

Effect of Benzalkonium Chloride Adaptation on Sensitivity to Antimicrobial Agents and Tolerance to Environmental Stresses in Listeria monocytogenes.

Listeria monocytogenes is an important food-borne pathogen that can persist in food processing environments and thus contaminate food products. Benzalkonium chloride (BC) is a common disinfectant widely used in food industry. Selective pressure associated with exposure to BC may result in adaptation to this agent in L. monocytogenes. In this study, the effect of BC adaptation on susceptibility to antimicrobial agents and tolerance to environmental stresses, as well as the role of efflux pumps in BC adaptation were investigated in Listeria monocytogenes. Exposure of L. monocytogenes to progressively increasing concentrations of BC led to adaptation not only to BC but also to several other antimicrobial agents with different modes of action, including cefotaxime, cephalothin, ciprofloxacin, and ethidium bromide (EtBr), indicating that the disinfectant BC has the ability to select for antibiotic resistance. Reserpine, an efflux pump inhibitor, reduced minimum inhibitory concentrations (MICs) of cephalosporins, ciprofloxacin, and EtBr in BC adapted strains, indicating that efflux pumps are involved in cross-adaptation to these antimicrobial agents. Our results showed that expression levels of the efflux pump MdrL in the BC adapted strains increased significantly relative to the corresponding wild-type strains (P < 0.05), with the highest increase in one BC adapted strain named HL06BCA. Moreover, the knockout mutant HL06BCAΔmdrL showed impaired growth compared to that of HL06BCA when exposed to 2 µg/ml of BC. It suggests that efflux pump MdrL is associated with BC adaptation in L. monocytogenes. However, we did not find mdrL to be associated with cross-adaptation to cephalosporins, ciprofloxacin, and EtBr in HL06BCA. Additionally, increased sensitivity to acid, alkali, osmotic, ethanol, and oxidative stresses was observed in most strains after repeated exposure to BC. These results suggest rotation of different disinfectant is helpful to maintain high effectiveness of BC toward L. monocytogenes and ethanol and hydrogen peroxide are at least the appropriate candidates.

Role of Efflux Pumps in the in vitro Development of Ciprofloxacin Resistance in Listeria monocytogenes.

Efflux is a primary fluoroquinolone resistance mechanism in Listeria monocytogenes. In the present study, ciprofloxacin resistant strains were selected by exposure of sensitive strain to progressively increasing concentrations of ciprofloxacin and then the roles of efflux pumps Lde and MdrL in the development of resistance to ciprofloxacin were also investigated in L. monocytogenes. Ciprofloxacin sensitive strain of L. monocytogenes exhibited reduced susceptibility to this antibiotic after induction. Cross-resistance to ethidium bromide (EtBr) was observed in ciprofloxacin-induced strains. However, cross-resistance to benzalkonium chloride (BC) did not occur in this study. Compared to the wild-type strain HL06, the expression levels of lde were increased in four ciprofloxacin-induced strains. The single-gene deletion mutants of lde and mdrL from the ciprofloxacin-induced resistant strain HL06CIP4 were constructed. However, decreased minimum inhibitory concentration (MIC) of ciprofloxacin was observed only in HL06CIP4Δlde compared to that of the parental strain HL06CIP4. Ciprofloxacin uptake appeared to be obviously increased in HL06CIP4Δlde in relative to HL06CIP4. These evidences suggested that efflux pump Lde is involved in ciprofloxacin resistance in L. monocytogenes HL06CIP4. The deletion of lexA had no effect on the expression levels of lde in HL06CIP4 in the absence or presence of ciprofloxacin, indicating that LexA was not involved in the regulation of efflux pump Lde in L. monocytogenes.

Efflux pump-mediated benzalkonium chloride resistance in Listeria monocytogenes isolated from retail food.

In this study, efflux pump-mediated benzalkonium chloride (BC) resistance, including plasmid-encoded (Qac protein family and BcrABC) and chromosome-borne efflux pumps, was investigated in Listeria monocytogenes from retail food in China. Among the 59 L. monocytogenes strains, 13 (22.0%) strains were resistant to BC. The PCR results showed that bcrABC was harbored by 2 of 13 BC resistant strains. However, none of the qac genes were detected among the 59 strains. The bcrABC was absent in both of the plasmid cured strains, indicating that this BC resistance determinant was plasmid-encoded in the two bcrABC-positive strains. In the presence of reserpine, most of the bcrABC-negative strains had decreases in the MICs of BC, suggesting the existence of other efflux pumps and their role in BC resistance. After exposed to reserpine, the reduction in BC MICs was observed in the two cured strains, indicating that efflux pumps located on chromosome was also involved in BC resistance. Our findings suggest that food products may act as reservoirs for BC resistant isolates of L. monocytogenes and plasmid- and chromosome-encoded efflux pumps could mediate the BC resistance of L. monocytogenes, which is especially relevant to the adaption of this organism in food-related environments with frequent BC use.

Detection of Extended-Spectrum ß-Lactamase and Plasmid-Mediated Quinolone Resistance Determinants in Escherichia coli Isolates from Retail Meat in China.

The aim of this study was to investigate the presence of extended-spectrum ß-lactamase (ESBL) and plasmid-mediated quinolone resistance (PMQR) genes in Escherichia coli isolated from retail meat samples in Henan Province, China. E. coli isolates were detected in 179 of 645 (27.7%) retail meat samples. Resistance of these isolates to antimicrobials was commonly observed, with 78.2% of isolates resistant to streptomycin, 74.3% resistant to tetracycline and 54.2% resistant to trimethoprim/sulfamethoxazole. Of the 179 isolates, 30 (16.7%) expressed ESBL, with blaTEM-1 (n = 17) and bla(CTX-M-14) (n = 9) most commonly mediating the ESBL phenotype. PMQR genes were present in 14 isolates (7.8%), with qnr and aac(6')-Ib-cr detected alone or in combination in nine (5.0%) and seven isolates (3.9%), respectively. The qnr genes detected included qnrS1 (n = 5), qnrA1 (n = 3), and qnrB4 (n = 1). The qepA gene was absent among these isolates. CTX-M-14 was the most prevalent ESBL type among the PMQR-positive isolates. The qnr and aac(6')-Ib-cr genes were found to co-reside and be co-transferred with blaCTX-M-14 or blaTEM-1 in five isolates. Our data suggest that retail meat may act as a reservoir for multi-resistant E. coli and may facilitate the dissemination of resistance genes.

Shedding of Fas ectodomain that affects apoptosis of hepatocytes occurring in regenerative liver.

BACKGROUND: On the basis of comprehending several membrane proteins undergoing ectodomain shedding, including tumor necrosis factor (TNF) alpha receptors, we want to know if Fas (CD95/APO-1), which belongs to the TNF receptor (TNFR) superfamily and transduces signals resulting in apoptosis upon binding of Fas ligand (L) or agonistic anti-Fas antibody, is shed on its ectodomain during liver regeneration METHODS: After purification of the total membrane protein of hepatocytes, we analyzed Fas ectodomain shedding, using Western blotting, and determined the effect of Fas shedding on the apoptosis of hepatocytes by a statistical method relevant to apoptosis. RESULTS: Fas protein ectodomain shedding occurred at 2, 12, and 36 h after partial hepatectomy, and its level decreased at 2 months after partial hepatectomy. The same results were gained from in-vitro cultured hepatocytes induced by serum from rats after partial hepatectomy. The sensitivity of hepatocytes to agonistic anti-Fas antibody increased significantly after they were treated with serum from rats after partial hepatectomy. However, the expression of Fas mRNA and Fas protein did not affect the liver regeneration. CONCLUSIONS: Fas ectodomain shedding might be an important mechanism in controlling hepatocyte apoptosis during liver regeneration.