A pepper mottle virus-based vector enables systemic expression of endoglucanase D in non-transgenic plants

Expression of an extremophilic xylanase in Nicotiana benthamiana and its use for the production of prebiotic xylooligosaccharides

A gene construct encoding a xylanase, which is active in extreme conditions of temperature and alkaline pH (90 °C, pH 10.5), has been transitorily expressed with high efficiency in Nicotiana benthamiana using a viral vector. The enzyme, targeted to the apoplast, accumulates in large amounts in plant tissues in as little as 7 days after inoculation, without detrimental effects on plant growth. The properties of the protein produced by the plant, in terms of resistance to temperature, pH, and enzymatic activity, are equivalent to those observed when Escherichia coli is used as a host. Purification of the plant-produced recombinant xylanase is facilitated by exporting the protein to the apoplastic space. The production of this xylanase by N. benthamiana, which avoids the hindrances derived from the use of E. coli, namely, intracellular production requiring subsequent purification, represents an important step for potential applications in the food industry in which more sustainable and green products are continuously demanded. As an example, the use of the enzyme producing prebiotic xylooligosdaccharides from xylan is here reported.

Pepper Mottle Virus and Its Host Interactions: Current State of Knowledge

Pepper mottle virus (PepMoV) is a destructive pathogen that infects various solanaceous plants, including pepper, bell pepper, potato, and tomato. In this review, we summarize what is known about the molecular characteristics of PepMoV and its interactions with host plants. Comparisons of symptom variations caused by PepMoV isolates in plant hosts indicates a possible relationship between symptom development and genetic variation. Researchers have investigated the PepMoV–plant pathosystem to identify effective and durable genes that confer resistance to the pathogen. As a result, several recessive pvr or dominant Pvr resistance genes that confer resistance to PepMoV in pepper have been characterized. On the other hand, the molecular mechanisms underlying the interaction between these resistance genes and PepMoV-encoded genes remain largely unknown. Our understanding of the molecular interactions between PepMoV and host plants should be increased by reverse genetic approaches and comprehensive transcriptomic analyses of both the virus and the host genes.

Targeted genome editing of plants and plant cells for biomanufacturing

Plants have provided humans with useful products since antiquity, but in the last 30 years they have also been developed as production platforms for small molecules and recombinant proteins. This initially niche area has blossomed with the growth of the global bioeconomy, and now includes chemical building blocks, polymers and renewable energy. All these applications can be described as “plant molecular farming” (PMF). Despite its potential to increase the sustainability of biologics manufacturing, PMF has yet to be embraced broadly by industry. This reflects a combination of regulatory uncertainty, limited information on process cost structures, and the absence of trained staff and suitable manufacturing capacity. However, the limited adaptation of plants and plant cells to the requirements of industry-scale manufacturing is an equally important hurdle. For example, the targeted genetic manipulation of yeast has been common practice since the 1980s, whereas reliable site-directed mutagenesis in most plants has only become available with the advent of CRISPR/Cas9 and similar genome editing technologies since around 2010. Here we summarize the applications of new genetic engineering technologies to improve plants as biomanufacturing platforms. We start by identifying current bottlenecks in manufacturing, then illustrate the progress that has already been made and discuss the potential for improvement at the molecular, cellular and organism levels. We discuss the effects of metabolic optimization, adaptation of the endomembrane system, modified glycosylation profiles, programmable growth and senescence, protease inactivation, and the expression of enzymes that promote biodegradation. We outline strategies to achieve these modifications by targeted gene modification, considering case-by-case examples of individual improvements and the combined modifications needed to generate a new general-purpose “chassis” for PMF.

Construction of stable infectious full-length and eGFP-tagged cDNA clones of Mirabilis crinkle mosaic virus via In-Fusion cloning

Mirabilis crinkle mosaic virus (MiCMV) was tentatively classified as a new member of the genus Potyvirus in the family Potyviridae in 2019. However, it was considered to be basella rugose mosaic virus based on the sequence similarity of the coat protein (CP) region. In this study, infectious MiCMV cDNA clones under the control of the 35S promoter were constructed with an In-Fusion cloning method. Systemically infected leaves of Mirabilis jalapa and Nicotiana benthamiana plants inoculated with pMiCMV and pMiCMV-NIb/eGFP had mosaic symptoms by 5 dpi. Infections were confirmed by a western blot analysis, electron microscopy, RT-PCR, and the inoculation of N. benthamiana seedlings with progeny virions. Systemic infections were not observed after Nicotiana glutinosa leaves were similarly inoculated, with eGFP fluorescence detected only in the inoculated leaves. Interestingly, the symptoms induced by pMiCMV and pMiCMV-NIb/eGFP were not similar to those caused by the wild-type MiCMV in Basella rubra plants. Moreover, RT-PCR analyses of B. rubra plants with virus-specific primers (MicpF and MicpR) indicated that a non-target fragment corresponding to the MiCMV CP coding region was amplified. This is the first report of the construction of a biologically active, full-length cDNA copy of the MiCMV RNA genome.

Plant-Based Cellulase Assay Systems as Alternatives for Synthetic Substrates

Dissociative enzymes such as cellulases are greatly desired for a variety of applications in the food, fuel, and fiber industries. Cellulases and other cell wall-degrading enzymes are currently being engineered with improved traits for application in the breakdown of lignocellulosic biomass. Biochemical assays using these "designer" enzymes have traditionally been carried out using synthetic substrates such as crystalline bacterial microcellulose (BMCC). However, the use of synthetic substrates may not reflect the actual action of these cellulases on real plant biomass. We examined the potential of suspension cell walls from several plant species as possible alternatives for synthetic cellulose substrates. Suspension cells grow synchronously; hence, their cell walls are more uniform than those derived from mature plants. This work will help to establish a new assay system that is more genuine than using synthetic substrates. In addition to this, we have demonstrated that it is feasible to produce cellulases inexpensively and at high concentrations and activities in plants using a recombinant plant virus expression system. Our long-term goals are to use this system to develop tailored cocktails of cellulases that have been engineered to function optimally for specific tasks (i.e., the conversion of biomass into biofuel or the enhancement of nutrients available in livestock feed). The broad impact would be to provide a facile and economic system for generating industrial enzymes that offer green solutions to valorize biomass in industrialized communities and specifically in developing countries.

Application of Reverse Genetics in Functional Genomics of Potyvirus

Numerous potyvirus studies, including virus biology, transmission, viral protein function, as well as virus–host interaction, have greatly benefited from the utilization of reverse genetic techniques. Reverse genetics of RNA viruses refers to the manipulation of viral genomes, transfection of the modified cDNAs into cells, and the production of live infectious progenies, either wild-type or mutated. Reverse genetic technology provides an opportunity of developing potyviruses into vectors for improving agronomic traits in plants, as a reporter system for tracking virus infection in hosts or a production system for target proteins. Therefore, this review provides an overview on the breakthroughs achieved in potyvirus research through the implementation of reverse genetic systems.

A plant intron enhances the performance of an infectious clone in planta

Although infectious clones are fundamental tools in virology and plant pathology, their efficacy is often reduced by the instability of viral sequences in Escherichia coli. In this study, we constructed an infectious clone of PepMoV (pPepMoV) in a bacterial binary vector (pSNU1); the clone induces symptoms of PepMoV in agroinfiltrated plants. During its modification and maintenance in E. coli, however, the pPepMoV infectious clone was instable in the bacteria. Manipulation of this unstable clone in the bacterial strain DH10B led to the spontaneous formation of a recombined clone with high stability in the bacteria but with reduced infectivity due to an unwanted insertion of an E. coli sequence in the NIa-protease coding region. Replacement of this sequence with a plant intron restored infectivity and maintained plasmid stability. In addition to restoring plasmid growth in both E. coli and Agrobacterium, the presence of the intron in the PepMoV sequence enhanced the accumulation of PepMoV in agroinfiltrated leaves and resulted in symptom induction in upper systemic leaves that was nearly as strong as with PepMoV sap-inoculation. Plant introns have been previously used to stabilize plasmids in E. coli without any effect or with an unexpected lag in symptom development. In contrast, the current results demonstrated the in vivo enhancement of an infectious clone by a plant intron.