Transgenic Elite Lines of Carioca Seeded Common Bean (Phaseolus Vulgaris L.) With Multiple Resistance to Viruses Reduce Cowpea Mild Mottle Virus Transmission

The most important viruses infecting common bean (Phaseolus vulgaris L.) in Brazil are BCMV, BGMV and CPMMV, the last two transmitted by the whitefly Bemisia tabaci, occurring simultaneously and causing severe yield losses. Genetically modified progenies of common bean, from carioca market class and multiple virus resistance (BCMV, BGMV and CPMMV), have been developed using conventional breeding and molecular tools. Agronomic performance and virus disease severity (VS) evaluated in two field trials, selected 39 elite progenies out of 477. Molecular analyses identified the presence of BCMV and BGMV resistance alleles in plants. CPMMV resistance was measured on mechanically inoculated plants using a VS scoring scale. Among the lowest VS average scores, five progenies showed resistance to BCMV, BGMV and CPMMV, and upright plant architecture, resistance to plant lodging and carioca market class grains, presenting potential to be developed into a new transgenic cultivar, with multiple virus resistance. Additionally, the resistant progenies may also contribute to reduce virus spread in the field, as they were a less efficient inoculum source of CPMMV in insect transmission assays.

Membrane Trafficking Proteins: A New Target to Identify Resistance to Viruses in Plants

Replication cycles from most simple-stranded positive RNA viruses infecting plants involve endomembrane deformations. Recent published data revealed several interactions between viral proteins and plant proteins associated with vesicle formation and movement. These plant proteins belong to the COPI/II, SNARE, clathrin and ESCRT endomembrane trafficking mechanisms. In a few cases, variations of these plant proteins leading to virus resistance have been identified. In this review, we summarize all known interactions between these plant cell mechanisms and viruses and highlight strategies allowing fast identification of variant alleles for membrane-associated proteins.

Evaluation of the biological effectiveness of inducers of resistance to viral diseases and their impact on potato yield in the field

Оценена биологическая эффективность Фармайода (йод) и Имуноцитофита (эфир арахидоновой кислоты) как индукторов устойчивости картофеля к вирусам в мелкоделяночных (г. Москва) и производственных опытах в Астраханской, Липецкой и Московской областях в 2015–2016 и 2018 годах. В Липецкой области картофель сорта Рамос заражен Y-вирусом картофеля (PVY) и комплексом вирусов M и S (PVM + PVS); в Астраханской области на сорте Импала отмечали комплексы PVM+PVS и PVM+PVS+PVY, в Московской области на сорте ВР-808 был отмечен Y-вирус. Биологическая эффективность Фармайода против Y-вируса в мелкоделяночных опытах на сорте Ред Скарлетт в 2015–2016 годах составила 76,4%, в 2018 году – 73,4%, а Иммуноцитофита – 47,4% и 48,4%. Прибавка урожайности от Фармайода была 21,6–34,4%, а от Иммуноцитофита – 17,0–21,3%. Против М-вируса на сорте Адретта биологическая эффективность Фармайода и Иммуноцитофита в 2015–2016 годах была 70,8% и 51,1%, в 2018 году – 56,5% и 41,3%. Урожайность в 2015–2016 годах увеличилась на 35,2% от применения Фармайода, от Иммуноцитофита – на 16,7%; в 2018 году прибавка – 24,0% и 15,3%, соответственно. В хозяйстве Московской области эффективность Фармайода составила 74,9%, предпосадочная обработка им клубней эффекта не дала. В Липецкой области биологическая эффективность Фармайода была в среднем 73%, Иммуноцитофита – 52%. Прибавка валовой урожайности от Фармайода – 9,1 т/га, Иммуноцитофита – 3,8 т/га, при урожайности в контроле 24,0 т/га; в 2016 году – 6,8 т/га и 3,3 т/га, в контроле – 19,5 т/га. В Астраханской области в 2016 году биологическая эффективность Фармайода – 73,2%, прибавка – 8,6 т/га, у Иммуноцитофита эти показатели – 53,2% и 5,2 т/га, в контроле 18,9 т/га. The biological effectiveness of Pharmaiod (100 g/l iodine) and Immunocitophyt (20 g/kg of ethylic ester of arachidonic acid) as inducers of potato resistance to viruses was evaluated in small plot trials (Moscow) and field experiments in the Astrakhan, Lipetsk and Moscow oblast in 2015–2016 and 2018. In the Lipetsk oblast, the potato variety Ramos was infected with the potato virus Y (PVY) and the complex infection of the potato viruses M and S (PVM + PVS); in Astrakhan oblast on Impala variety, the PVM + PVS and PVM + PVS + PVY virus complexes were noted; in Moscow oblast the potato variety VR-808 was infected with PVY. In 2015–2016 in small plot trials the biological effectiveness of Pharmaiod against PVY on Red Scarlet variety averaged 76.4%, in 2018–73.4% and Immunocitophyt – 47.4% and 48.4%. The yield increase from the use Pharmaiod was 21.6–34.4%, and from Immunocitophyt – 17.0–21.3%. The biological effectiveness of Pharmaiod and Immunocitophyt against the M-virus on Adretta variety in 2015–2016 was 70.8% and 51.1%, in 2018–56.5% and 41.3%. The total yield in 2015–2016 increased by 35.2% from the use of Pharmaiod, from Immunocytofit by 16.7%, in 2018, the increase was by 24.0% and 15.3%, respectively. In the farm of Moscow Oblast, the effectiveness of Pharmaiod was 74.9%, the pre-planting treatment of tubers did not have a significant effect. In Lipetsk oblast, the biological effectiveness of Pharmaiod averaged 73%, Immunocitophyt – 52%. The total yield increase from the use Pharmaiod is 9.1 t/ha, from Immunocitophyt – 3.8 t/ha, when the yield in the control variant was 24.0 t/ha; in 2016–6.8 t/ha and 3.3 t/ha, in control – 19.5 t/ha. In 2016 in Astrakhan oblast the biological effectiveness of Pharmaiod was 73.2%, the increase was 8.6 t/ha, in Immunocitophyt these rates were 53.2% and 5.2 t/ha, in the control 18.9 t/ha.

Regulation of plant antiviral defense genes via host RNA-silencing mechanisms

Background Plants in nature or crops in the field interact with a multitude of beneficial or parasitic organisms, including bacteria, fungi and viruses. Viruses are highly specialized to infect a limited range of host plants, leading in extreme cases to the full invasion of the host and a diseased phenotype. Resistance to viruses can be mediated by various passive or active mechanisms, including the RNA-silencing machinery and the innate immune system. Main text RNA-silencing mechanisms may inhibit viral replication, while viral components can elicit the innate immune system. Viruses that successfully enter the plant cell can elicit pattern-triggered immunity (PTI), albeit by yet unknown mechanisms. As a counter defense, viruses suppress PTI. Furthermore, viral Avirulence proteins (Avr) may be detected by intracellular immune receptors (Resistance proteins) to elicit effector-triggered immunity (ETI). ETI often culminates in a localized programmed cell death reaction, the hypersensitive response (HR), and is accompanied by a potent systemic defense response. In a dichotomous view, RNA silencing and innate immunity are seen as two separate mechanisms of resistance. Here, we review the intricate connections and similarities between these two regulatory systems, which are collectively required to ensure plant fitness and resilience. Conclusions The detailed understanding of immune regulation at the transcriptional level provides novel opportunities for enhancing plant resistance to viruses by RNA-based technologies. However, extensive use of RNA technologies requires a thorough understanding of the molecular mechanisms of RNA gene regulation. We describe the main examples of host RNA-mediated regulation of virus resistance.

An isoform of Dicer protects mammalian stem cells against multiple RNA viruses

In mammals, early resistance to viruses relies on interferons, which protect differentiated cells but not stem cells from viral replication. Many other organisms rely instead on RNA interference (RNAi) mediated by a specialized Dicer protein that cleaves viral double-stranded RNA. Whether RNAi also contributes to mammalian antiviral immunity remains controversial. We identified an isoform of Dicer, named antiviral Dicer (aviD), that protects tissue stem cells from RNA viruses—including Zika virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)—by dicing viral double-stranded RNA to orchestrate antiviral RNAi. Our work sheds light on the molecular regulation of antiviral RNAi in mammalian innate immunity, in which different cell-intrinsic antiviral pathways can be tailored to the differentiation status of cells.

Extreme Resistance to Viruses in Potato and Soybean

Plant pathogens, including viruses, negatively impact global crop production. Plants have evolved complex immune responses to pathogens. These responses are often controlled by nucleotide-binding leucine-rich repeat proteins (NLRs), which recognize intracellular, pathogen-derived proteins. Genetic resistance to plant viruses is often phenotypically characterized by programmed cell death at or near the infection site; a reaction termed the hypersensitive response. Although visualization of the hypersensitive response is often used as a hallmark of resistance, the molecular mechanisms leading to the hypersensitive response and associated cell death vary. Plants with extreme resistance to viruses rarely exhibit symptoms and have little to no detectable virus replication or spread beyond the infection site. Both extreme resistance and the hypersensitive response can be activated by the same NLR genes. In many cases, genes that normally provide an extreme resistance phenotype can be stimulated to cause a hypersensitive response by experimentally increasing cellular levels of pathogen-derived elicitor protein(s). The molecular mechanisms of extreme resistance and its relationship to the hypersensitive response are largely uncharacterized. Studies on potato and soybean cultivars that are resistant to strains of Potato virus Y (PVY), Potato virus X (PVX), and Soybean mosaic virus (SMV) indicate that abscisic acid (ABA)-mediated signaling and NLR nuclear translocation are important for the extreme resistance response. Recent research also indicates that some of the same proteins are involved in both extreme resistance and the hypersensitive response. Herein, we review and synthesize published studies on extreme resistance in potato and soybean, and describe studies in additional species, including model plant species, to highlight future research avenues that may bridge the gaps in our knowledge of plant antiviral defense mechanisms.

Rapid evolutionary turnover of mobile genetic elements drives microbial resistance to viruses

Although it is generally accepted that viruses (phages) drive bacterial evolution, how these dynamics play out in the wild remains poorly understood. Here we show that the arms race between phages and their hosts is mediated by large and highly diverse mobile genetic elements. These phage-defense elements display exceedingly fast evolutionary turnover, resulting in differential phage susceptibility among clonal bacterial strains while phage receptors remain invariant. Protection afforded by multiple elements is cumulative, and a single bacterial genome can harbor as many as 18 putative phage-defense elements. Overall, elements account for 90% of the flexible genome amongst closely related strains. The rapid turnover of these elements demonstrates that phage resistance is unlinked from other genomic features and that resistance to phage therapy might be as easily acquired as antibiotic resistance.

Towards plant resistance to viruses using protein-only RNase P

Plant viruses cause massive crop yield loss worldwide. Most plant viruses are RNA viruses, many of which contain a functional tRNA-like structure. RNase P has the enzymatic activity to catalyze the 5′ maturation of precursor tRNAs. It is also able to cleave tRNA-like structures. However, RNase P enzymes only accumulate in the nucleus, mitochondria, and chloroplasts rather than cytosol where virus replication takes place. Here, we report a biotechnology strategy based on the re-localization of plant protein-only RNase P to the cytosol (CytoRP) to target plant viruses tRNA-like structures and thus hamper virus replication. We demonstrate the cytosol localization of protein-only RNase P in Arabidopsis protoplasts. In addition, we provide in vitro evidences for CytoRP to cleave turnip yellow mosaic virus and oilseed rape mosaic virus. However, we observe varied in vivo results. The possible reasons have been discussed. Overall, the results provided here show the potential of using CytoRP for combating some plant viral diseases.

Engineering crops of the future: CRISPR approaches to develop climate-resilient and disease-resistant plants

To meet increasing global food demand, breeders and scientists aim to improve the yield and quality of major food crops. Plant diseases threaten food security and are expected to increase because of climate change. CRISPR genome-editing technology opens new opportunities to engineer disease resistance traits. With precise genome engineering and transgene-free applications, CRISPR is expected to resolve the major challenges to crop improvement. Here, we discuss the latest developments in CRISPR technologies for engineering resistance to viruses, bacteria, fungi, and pests. We conclude by highlighting current concerns and gaps in technology, as well as outstanding questions for future research.

Balance between promiscuity and specificity in phage λ host range

As hosts acquire resistance to viruses, viruses must overcome that resistance to re-establish infectivity, or go extinct. Despite the significant hurdles associated with adapting to a resistant host, viruses are evolutionarily successful and maintain stable coevolutionary relationships with their hosts. To investigate the factors underlying how pathogens adapt to their hosts, we performed a deep mutational scan of the region of the λ tail fiber tip protein that mediates contact with the λ host, E. coli. Phages harboring amino acid substitutions were subjected to selection for infectivity on wild type E. coli, revealing a highly restrictive fitness landscape, in which most substitutions completely abrogate function. By comparing this lack of mutational tolerance to evolutionary diversity, we highlight a set of mutationally intolerant and diverse positions associated with host range expansion. Imposing selection for infectivity on three λ-resistant hosts, each harboring a different missense mutation in the λ receptor, reveals hundreds of adaptive variants in λ. We distinguish λ variants that confer promiscuity, a general ability to overcome host resistance, from those that drive host-specific infectivity. Both processes may be important in driving adaptation to a novel host.