Harnessing a Transient Gene Expression System in Nicotiana benthamiana to Explore Plant Agrochemical Transporters

Metabolic mechanism, responses, and functions of genes HDH1, HDH3, and GST1 of tea (Camellia sinensis L.) to the insecticide thiamethoxam

Misuse of insecticides such as thiamethoxam (TMX) not only affects the quality of tea but also leaves residues in tea. Therefore, exploring the metabolic mechanisms of TMX in tea plants can evaluate effects of pesticides on the environment and human health. Here, effects of TMX on tea plants were studied. Malondialdehyde (MDA) content reached a maximum of 12.59 nmol/g fresh weight (FW) on 1st d under X (the recommended dose: 0.015 kg a.i./ha) of TMX. Under 2 X (0.03 kg a.i./ha), the catalase, glutathione S-transferase and superoxide dismutase activity were increased by 45.0 %, 55.5 %, and 49.7 % at 7 d respectively. Metabolomic and transcriptomic analyses revealed that TMX significantly affected amino acid metabolism, flavonoid biosynthesis and glutathione metabolism, and induced the expression of 3-hydroxyisobutyric acid dehydrogenase genes (CsHDH1 and CsHDH3) and glutathione S-transferase gene (CsGST1). The three genes were transiently expressed in Nicotiana benthamiana for the first time to verify the function of TMX degradation, with the degradation rate of 59.2 %-85.3 % at X. This study elucidated the response of tea plants to abiotic stress on the molecular-scale perspective, and the molecular approaches could serve as a model for the study on pesticide metabolism in plants. SYNOPSIS: Degradation ability of CsHDH1, CsHDH3 and CsGST1 genes to thiamethoxam was verified for the first time, providing genetic resources for phytoremediation of pollutants.

Improvement of plant quality by amino acid transporters: A comprehensive review

Amino acids serve as the primary means of transport and organic nitrogen carrier in plants, playing an essential role in plant growth and development. Amino acid transporters (AATs) facilitate the movement of amino acids within plants and have been identified and characterised in a number of species. It has been demonstrated that these amino acid transporters exert an influence on the quality attributes of plants, in addition to their primary function of transporting amino acid transport. This paper presents a summary of the role of AATs in plant quality improvement. This encompasses the enhancement of nitrogen utilization efficiency, root development, tiller number and fruit yield. Concurrently, AATs can bolster the resilience of plants to pests, diseases and abiotic stresses, thereby further enhancing the yield and quality of fruit. AATs exhibit a wide range of substrate specificity, which greatly optimizes the use of pesticides and significantly reduces pesticide residues, and reduces the risk of environmental pollution while increasing the safety of fruit. The discovery of AATs function provides new ideas and ways to cultivate high-quality crop and promote changes in agricultural development, and has great potential in the application of plant quality improvement.

Transient expression of anti-HrpE scFv antibody reduces the hypersensitive response in non-host plant against bacterial phytopathogen Xanthomonas citri subsp. citri

Citrus canker is a bacterial disease caused by Xanthomonas citri subsp. citri (Xcc) that affects the citrus industry worldwide. Hrp pili subunits (HrpE), an essential component of Type III secretion system (T3SS) bacteria, play a crucial role in the pathogenesis of Xcc by transporting effector proteins into the host cell and causing canker symptoms. Therefore, development of antibodies that block HrpE can suppress disease progression. In this study, a specific scFv detecting HrpE was developed using phage display technique and characterized using sequencing, ELISA, Western blotting, and molecular docking. In addition, a plant expression vector of pCAMBIA-scFvH6 was constructed and agroinfiltrated into Nicotiana tabacum cv. Samson leaves. The hypersensitive response (HR) in the leaves of transformed and non-transformed plants was evaluated by inoculating leaves with Xcc. After three rounds of biopanning of the phage library, a specific human scFv antibody, named scFvH6, was identified that showed high binding activity against HrpE in ELISA and Western blotting. Molecular docking results showed that five intermolecular hydrogen bonds are involved in HrpE-scFvH6 interaction, confirming the specificity and high binding activity of scFvH6. Successful transient expression of pCAMBIA-scFvH6 in tobacco leaves was verified using immunoassay tests. The binding activity of plant-produced scFvH6 to detect HrpE in Western blotting and ELISA was similar to that of bacterial-produced scFvH6 antibody. Interestingly, tobacco plants expressing scFvH6 showed a remarkable reduction in HR induced by Xcc compared with control plants, so that incidence of necrotic lesions was significantly higher in non-transformed controls (≥ 1.5 lesions/cm2) than in the plants producing scFvH6 (≤ 0.5 lesions/cm2) after infiltration with Xcc inoculum. Our results revealed that the expression of scFvH6 in tobacco leaves can confer resistance to Xcc, indicating that this approach could be considered to provide resistance to citrus bacterial canker disease.

An Agrobacterium-Mediated Transient Expression Method for Functional Assay of Genes Promoting Disease in Monocots

Agrobacterium-mediated transient expression (AMTE) has been widely used for high-throughput assays of gene function in diverse plant species. However, its application in monocots is still limited due to low expression efficiency. Here, by using histochemical staining and a quantitative fluorescence assay of β-glucuronidase (GUS) gene expression, we investigated factors affecting the efficiency of AMTE on intact barley plants. We found prominent variation in GUS expression levels across diverse vectors commonly used for stable transformation and that the vector pCBEP produced the highest expression. Additionally, concurrent treatments of plants with one day of high humidity and two days of darkness following agro-infiltration also significantly increased GUS expression efficiency. We thus established an optimized method for efficient AMTE on barley and further demonstrated its efficiency on wheat and rice plants. We showed that this approach could produce enough proteins suitable for split-luciferase assays of protein-protein interactions on barley leaves. Moreover, we incorporated the AMTE protocol into the functional dissection of a complex biological process such as plant disease. Based on our previous research, we used the pCBEP vector to construct a full-length cDNA library of genes upregulated during the early stage of rice blast disease. A subsequent screen of the library by AMTE identified 15 candidate genes (out of ~2000 clones) promoting blast disease on barley plants. Four identified genes encode chloroplast-related proteins: OsNYC3, OsNUDX21, OsMRS2-9, and OsAk2. These genes were induced during rice blast disease; however, constitutive overexpression of these genes conferred enhanced disease susceptibility to Colletotrichum higginsianum in Arabidopsis. These observations highlight the power of the optimized AMTE approach on monocots as an effective tool for facilitating functional assays of genes mediating complex processes such as plant-microbe interactions.

Characterization of three tandem-duplicated calcium binding protein (CaBP) genes and promoters reveals their roles in the phytohormone and wounding responses in citrus

Accumulated evidences have revealed the critical roles of calcium binding protein (CaBP) in growth and stress responses of plants. However, its function in woody plants is poorly understood. In this study, we cloned the CDS, gDNA and promoter sequences of three tandem-duplicated CaBPs (CsCaBP1, CsCaBP2 and CsCaBP3) from Citrus sinensis, analyzed their sequence characteristics, and investigated their gene expression patterns and promoter activities under treatments of CaCl₂, several phytohormones and wounding. Results showed that the three CsCaBPs have high sequence similarity. Their expression was strongly induced by CaCl₂, ethylene, jasmonic acid, salicylic acid and wounding, and the promoting effect of wounding on their expression was found to be partially ethylene-dependent. Consistently, we identified many phytohormone-related cis-acting elements in their promoters, and their promoter activity could be induced significantly by ethylene, jasmonic acid, salicylic acid and wounding. All the three CsCaBPs can interact with WRKY40, whose encoding gene showed a similar expression pattern to CsCaBPs under phytohormone and wounding treatments. In addition, CsERF14, CsERF21, CsERF3 and CsERF2 could bind to their promoters. The results obtained in this study indicated that the three duplicated CsCaBPs were functionally redundant and played similar roles in the phytohormone and wounding responses of C. sinensis.

Plant Secondary Metabolite Transporters: Diversity, Functionality, and Their Modulation

Secondary metabolites (SMs) play crucial roles in the vital functioning of plants such as growth, development, defense, and survival via their transportation and accumulation at the required site. However, unlike primary metabolites, the transport mechanisms of SMs are not yet well explored. There exists a huge gap between the abundant presence of SM transporters, their identification, and functional characterization. A better understanding of plant SM transporters will surely be a step forward to fulfill the steeply increasing demand for bioactive compounds for the formulation of herbal medicines. Thus, the engineering of transporters by modulating their expression is emerging as the most viable option to achieve the long-term goal of systemic metabolic engineering for enhanced metabolite production at minimum cost. In this review article, we are updating the understanding of recent advancements in the field of plant SM transporters, particularly those discovered in the past two decades. Herein, we provide notable insights about various types of fully or partially characterized transporters from the ABC, MATE, PUP, and NPF families including their diverse functionalities, structural information, potential approaches for their identification and characterization, several regulatory parameters, and their modulation. A novel perspective to the concept of "Transporter Engineering" has also been unveiled by highlighting its potential applications particularly in plant stress (biotic and abiotic) tolerance, SM accumulation, and removal of anti-nutritional compounds, which will be of great value for the crop improvement program. The present study creates a roadmap for easy identification and a better understanding of various transporters, which can be utilized as suitable targets for transporter engineering in future research.