Simultaneous RNAi Knockdown of Three FMRFamide-Like Peptide Genes, Mi-flp1, Mi-flp12, and Mi-flp18 Provides Resistance to Root-Knot Nematode, Meloidogyne incognita

Unraveling the enigma of root-knot nematodes: from origins to advanced management strategies in agriculture

MAIN CONCLUSION

Integrated management strategies, including novel nematicides and resilient cultivars, offer sustainable solutions to combat root-knot nematodes, crucial for safeguarding global agriculture against persistent threats. Root-knot nematodes (RKN) pose a significant threat to a diverse range of host plants, with their obligatory endoparasitic nature leading to substantial agricultural losses. RKN spend much of their lives inside or in contact by secreting plant cell wall-modifying enzymes resulting in the giant cell development for establishing host-parasite relationships. Additionally, inflicting physical harm to host plants, RKN also contributes to disease complexes creation with fungi and bacteria. This review comprehensively explores the origin, history, distribution, and physiological races of RKN, emphasizing their economic impact on plants through gall formation. Management strategies, ranging from cultural and physical to biological and chemical controls, along with resistance mechanisms and marker-assisted selection, are explored. While recognizing the limitations of traditional nematicides, recent breakthroughs in non-fumigant alternatives like fluensulfone, spirotetramat, and fluopyram offer promising avenues for sustainable RKN management. Despite the success of resistance mechanisms like the Mi gene, challenges persist, prompting the need for integrative approaches to tackle Mi-virulent isolates. In conclusion, the review stresses the importance of innovative and resilient control measures for sustainable agriculture, emphasizing ongoing research to address evolving challenges posed by RKN. The integration of botanicals, resistant cultivars, and biological controls, alongside advancements in non-fumigant nematicides, contributes novel insights to the field, laying the ground work for future research directions to ensure the long-term sustainability of agriculture in the face of persistent RKN threats.

Host-induced RNA interference targeting the neuromotor gene FMRFamide-like peptide-14 (Mi-flp14) perturbs Meloidogyne incognita parasitic success in eggplant

KEY MESSAGE

The study demonstrates the successful management of Meloidogyne incognita in eggplant using Mi-flp14 RNA interference, showing reduced nematode penetration and reproduction without off-target effects across multiple generations. Root-knot nematode, Meloidogyne incognita, causes huge yield losses worldwide. Neuromotor function in M. incognita governed by 19 neuropeptides is vital for parasitism and parasite biology. The present study establishes the utility of Mi-flp14 for managing M. incognita in eggplant in continuation of our earlier proof of concept in tobacco (US patent US2015/0361445A1). Mi-flp14 hairpin RNA construct was used for generating 19 independent transgenic eggplant events. PCR and Southern hybridization analysis confirmed transgene integration and its orientation, while RT-qPCR and Northern hybridization established the generation of dsRNA and siRNA of Mi-flp14. In vitro and in vivo bio-efficacy analysis of single-copy events against M. incognita showed reduced nematode penetration and development at various intervals that negatively impacted reproduction. Interestingly, M. incognita preferred wild-type plants over the transgenics even when unbiased equal opportunity was provided for the infection. A significant reduction in disease parameters was observed in transgenic plants viz., galls (40-48%), females (40-50%), egg masses (35-40%), eggs/egg mass (50-55%), and derived multiplication factor (60-65%) compared to wild type. A unique demonstration of perturbed expression of Mi-flp14 in partially penetrated juveniles and female nematodes established successful host-mediated RNAi both at the time of penetration even before the nematodes started withdrawing plant nutrients and later stage, respectively. The absence of off-target effects in transgenic plants was supported by the normal growth phenotype of the plants and T-DNA integration loci. Stability in the bio-efficacy against M. incognita across T1- to T4-generation transgenic plants established the utility of silencing Mi-flp14 for nematode management. This study demonstrates the significance of targeting Mi-flp14 in eggplant for nematode management, particularly to address global agricultural challenges posed by M. incognita.

Exploring the putative microRNAs cross-kingdom transfer in Solanum lycopersicum-Meloidogyne incognita interactions

Introduction

Plant-pathogen interaction is an inexhaustible source of information on how to sustainably control diseases that negatively affect agricultural production. Meloidogyne incognita is a root-knot nematode (RKN), representing a pest for many crops, including tomato (Solanum lycopersicum). RKNs are a global threat to agriculture, especially under climate change, and RNA technologies offer a potential alternative to chemical nematicides. While endogenous microRNAs have been identified in both S. lycopersicum and M. incognita, and their roles have been related to the regulation of developmental changes, no study has investigated the miRNAs cross-kingdom transfer during this interaction.

Methods

Here, we propose a bioinformatics pipeline to highlight potential miRNA-dependent cross-kingdom interactions between tomato and M. incognita.

Results

The obtained data show that nematode miRNAs putatively targeting tomato genes are mostly related to detrimental effects on plant development and defense. Similarly, tomato miRNAs putatively targeting M. incognita biological processes have negative effects on digestion, mobility, and reproduction. To experimentally test this hypothesis, an in vitro feeding assay was carried out using sly-miRNAs selected from the bioinformatics approach. The results show that two tomato miRNAs (sly-miRNA156a, sly-miR169f) soaked by juvenile larvae (J2s) affected their ability to infect plant roots and form galls. This was also coupled with a significant downregulation of predicted target genes (Minc11367, Minc00111), as revealed by a qRT-PCR analysis.

Discussions

Therefore, the current study expands the knowledge related to the cross-kingdom miRNAs involvement in host-parasite interactions and could pave the way for the application of exogenous plant miRNAs as tools to control nematode infection.

Advances in RNA Interference for Plant Functional Genomics: Unveiling Traits, Mechanisms, and Future Directions

RNA interference (RNAi) is a conserved molecular mechanism that plays a critical role in post-transcriptional gene silencing across diverse organisms. This review delves into the role of RNAi in plant functional genomics and its applications in crop improvement, highlighting its mechanistic insights and practical implications. The review begins with the foundational discovery of RNAi's mechanism, tracing its origins from petunias to its widespread presence in various organisms. Various classes of regulatory non-coding small RNAs, including siRNAs, miRNAs, and phasiRNAs, have been uncovered, expanding the scope of RNAi-mediated gene regulation beyond conventional understanding. These RNA classes participate in intricate post-transcriptional and epigenetic processes that influence gene expression. In the context of crop enhancement, RNAi has emerged as a powerful tool for understanding gene functions. It has proven effective in deciphering gene roles related to stress resistance, metabolic pathways, and more. Additionally, RNAi-based approaches hold promise for integrated pest management and sustainable agriculture, contributing to global efforts in food security. This review discusses RNAi's diverse applications, such as modifying plant architecture, extending shelf life, and enhancing nutritional content in crops. The challenges and future prospects of RNAi technology, including delivery methods and biosafety concerns, are also explored. The global landscape of RNAi research is highlighted, with significant contributions from regions such as China, Europe, and North America. In conclusion, RNAi remains a versatile and pivotal tool in modern plant research, offering novel avenues for understanding gene functions and improving crop traits. Its integration with other biotechnological approaches such as gene editing holds the potential to shape the future of agriculture and sustainable food production.

Metabolic variations in root tissues and rhizosphere soils of weak host plants potently lead to distinct host status and chemotaxis regulation of Meloidogyne incognita in intercropping

Root-knot nematodes (RKNs) inflict extensive damage to global agricultural production. Intercropping has been identified as a viable agricultural tool for combating RKNs, but the mechanisms by which intercropped plants modulate RKN parasitism are still not well understood. Here, we focus on the cucumber-amaranth intercropping system. We used a range of approaches, including the attraction assay, in vitro RNA interference (RNAi), untargeted metabolomics, and hairy root transformation, to unveil the mechanisms by which weak host plants regulate Meloidogyne incognita chemotaxis towards host plants and control infection. Amaranth roots showed a direct repellence to M. incognita through disrupting its chemotaxis. The in vitro RNAi assay demonstrated that the Mi-flp-1 and Mi-flp-18 genes (encoding FMRFamide-like peptides) regulated M. incognita chemotaxis towards cucumber and controlled infection. Moreover, M. incognita infection stimulated cucumber and amaranth to accumulate distinct metabolites in both root tissues and rhizosphere soils. In particular, naringenin and salicin, enriched specifically in amaranth rhizosphere soils, inhibited the expression of Mi-flp-1 and Mi-flp-18. In addition, overexpression of genes involved in the biosynthesis of pantothenic acid and phloretin, both of which were enriched specifically in amaranth root tissues, delayed M. incognita development in cucumber hairy roots. Together, our results reveal that both the distinct host status and disruption of chemotaxis contribute to M. incognita inhibition in intercropping.

Root-knot nematode infections and soil characteristics significantly affected microbial community composition and assembly of tobacco soil microbiota: a large-scale comparison in tobacco-growing areas

Introduction

Tobacco root-knot nematode (RKN) is a highly destructive soil-borne disease worldwide. However, there is a lack of research on the relationship between RKN and tobacco root microbial community composition under large-scale geographical conditions in China.

Methods

In this study, we collected 65 samples from 28 main tobacco-growing areas across 10 provinces in China and conducted 16S rDNA sequencing to investigate the dynamic microbial changes in tobacco soil infected by RKN compared to healthy tobacco soil. Based on the analysis of rhizosphere soil bacterial communities, changes after RKN infection, and soil environmental factors.

Results

We found the 28 tobacco-growing areas could be divided into two distinct groups with different microbial compositions and varying responses to RKN infection. In group1 of the provinces of Anhui, Henan, Shanxi, and Heilongjiang, Vicinamibacteria dominated the bacterial community, while Acidobacteriae was present in low abundance. In contrast, group2 of the other six provinces (Yunnan, Guizhou, Chongqing, Guangxi, Hubei, and Shandong) exhibited an opposite pattern. After infected by RKN, the genera Chitinophaga increased significant in group 1, while the genera Rhodococcus in group 2 exhibited a substantial increase. Alpha-diversity analysis revealed that RKN-infected tobacco exhibited a richer and more diverse rhizosphere soil bacterial community compared to healthy tobacco in most growing areas. A total of 12 kinds of soil environmental factors were measured in healthy and RKN-infected tobacco soil, and based on the co-occurrence and correlation analysis between environmental factors and microbial species, the pH level, calcium (Ca), magnesium (Mg), phosphorus (P), iron (Fe), and sodium (Na) were identified as key environmental factors influencing the population composition of rhizosphere microorganisms during RKN infection. We observed that RKN infection further increased the pH in weakly alkaline group 1 soil, while weakly acidic group 2 soil experienced a further decrease in pH. Furthermore, we identified three genera as potential biocontrol or plant growth-promoting bacteria for tobacco.

Discussion

These findings provide valuable reference data for managing RKN disease in different tobacco-growing areas and contribute to the exploration of new and effective biological control methods.

Comparative Root Transcriptome Profiling and Gene Regulatory Network Analysis between Eastern and Western Carrot (Daucus carota L.) Cultivars Reveals Candidate Genes for Vascular Tissue Patterning

Carrot (Daucus carota L.) is a highly consumed vegetable rich in carotenoids, known for their potent antioxidant, anti-inflammatory, and immune-protecting properties. While genetic and molecular studies have largely focused on wild and Western carrot cultivars (cvs), little is known about the evolutionary interactions between closely related Eastern and Western cvs. In this study, we conducted comparative transcriptome profiling of root tissues from Eastern (UHSBC-23-1) and Western (UHSBC-100) carrot cv. to better understand differentially expressed genes (DEGs) associated with storage root development and vascular cambium (VC) tissue patterning. Through reference-guided TopHat mapping, we achieved an average mapping rate of 73.87% and identified a total of 3544 DEGs (p < 0.05). Functional annotation and gene ontology classification revealed 97 functional categories, including 33 biological processes, 19 cellular components, 45 metabolic processes, and 26 KEGG pathways. Notably, Eastern cv. exhibited enrichment in cell wall, plant-pathogen interaction, and signal transduction terms, while Western cv. showed dominance in photosynthesis, metabolic process, and carbon metabolism terms. Moreover, constructed gene regulatory network (GRN) for both cvs. obtained orthologs with 1222 VC-responsive genes of Arabidopsis thaliana. In Western cv, GRN revealed VC-responsive gene clusters primarily associated with photosynthetic processes and carbon metabolism. In contrast, Eastern cv. exhibited a higher number of stress-responsive genes, and transcription factors (e.g., MYB15, WRKY46, AP2/ERF TF connected via signaling pathways with NAC036) were identified as master regulators of xylem vessel differentiation and secondary cell wall thickening. By elucidating the comparative transcriptome profiles of Eastern and Western cvs. for the first time, our study provides valuable insights into the differentially expressed genes involved in root development and VC tissue patterning. The identification of key regulatory genes and their roles in these processes represents a significant advancement in our understanding of the evolutionary relations and molecular mechanisms underlying secondary growth of carrot and regulation by vascular cambium.

Tweaking the Small Non-Coding RNAs to Improve Desirable Traits in Plant

Plant transcriptome contains an enormous amount of non-coding RNAs (ncRNAs) that do not code for proteins but take part in regulating gene expression. Since their discovery in the early 1990s, much research has been conducted to elucidate their function in the gene regulatory network and their involvement in plants' response to biotic/abiotic stresses. Typically, 20-30 nucleotide-long small ncRNAs are a potential target for plant molecular breeders because of their agricultural importance. This review summarizes the current understanding of three major classes of small ncRNAs: short-interfering RNAs (siRNAs), microRNA (miRNA), and transacting siRNAs (tasiRNAs). Furthermore, their biogenesis, mode of action, and how they have been utilized to improve crop productivity and disease resistance are discussed here.

Metagenomic insights into the changes in the rhizosphere microbial community caused by the root-knot nematode Meloidogyne incognita in tobacco

Root-knot nematode (RKN) disease is a destructive soil disease that affects crop health and causes huge losses in crop production. To explore the relationships between soil environments, rhizobacterial communities, and plant health, rhizosphere bacterial communities were analyzed using metagenomic sequencing in tobacco samples with different grades of RKN disease. The results showed that the community structure and function of the plant rhizosphere were significantly correlated to the RKN disease. RKN density and urease content were key factors affecting the rhizosphere bacterial community. Urease accelerated the catabolism of urea and led to the production of high concentrations of ammonia, which directly suppressed the development of RKNs or by improving the nutritional and growth status of microorganisms that were antagonistic to RKNs. Further experiments showed that the suppression role of ammonia should be attributed to the direct inhibition of NH₃. The bacterial members that were positively correlated with RKN density, contained many plant cell wall degrading enzymes, which might destroy plant cell walls and promote the colonization of RKN in tobacco roots. The analysis of metatranscriptome and metabolism demonstrated the role of these cell wall degrading enzymes. This study offers a comprehensive insight into the relationships between RKNs, bacteria, and soil environmental factors and provides new ideas for the biological control of RKNs.

Host-delivered RNAi-mediated silencing using fusion cassettes of different functional groups of genes precludes Meloidogyne incognita multiplication in Nicotiana tabacum

This study demonstrates multi-gene silencing approach for simultaneous silencing of several functional genes through a fusion gene strategy for protecting plants against root-knot nematode, Meloidogyne incognita. The ability of root-knot nematode (RKN), Meloidogyne incognita, to cause extensive yield decline in a wide range of cultivated crops is well-documented. Due to the inadequacies of current management approaches, the alternatively employed contemporary RNA interference (RNAi)-based host-delivered gene silencing (HD-RNAi) strategy targeting different functional effectors/genes has shown substantial potential to combat RKNs. In this direction, we have explored the possibility of simultaneous silencing of four esophageal gland genes, six plant cell-wall modifying enzymes (PCWMEs) and a serine protease gene of M. incognita using the fusion approach. In vitro RNAi showed that combinatorial gene silencing is the most effective in affecting nematode behavior in terms of reduced attraction, penetration, development, and reproduction in tomato and adzuki beans. In addition, qRT-PCR analysis of M. incognita J2s soaked in fusion-dsRNA showed perturbed expression of all the genes comprising the fusion construct confirming successful dsRNA processing which is also supported by increased mRNA abundance of five key-RNAi pathway genes. In addition, hairpin RNA expressing constructs of multi-gene fusion cassettes were developed and used for generation of Nicotiana tabacum transgenic plants. The integration of gene constructs and expression of siRNAs in transgenic events were confirmed by Southern and Northern blot analyses. Besides, bio-efficacy analyses of transgenic events, conferred up to 87% reduction in M. incognita multiplication. Correspondingly, reduced transcript accumulation of the target genes in the M. incognita females extracted from transgenic events confirmed successful gene silencing.

A novel tasi RNA-based micro RNA-induced gene silencing strategy to tackle multiple pests and pathogens in cotton (Gossypium hirsutum L.)

This study demonstrates the combinatorial management of multiple pests through a trans-acting siRNA (tasiRNA)-based micro RNA-induced gene silencing (MIGS) strategy. Transgenic cotton events demonstrated improved efficacy against cotton leaf curl disease, cotton leaf hopper and root-knot nematode. Cotton (Gossypium hirsutum L.), an important commercial crop grown worldwide is confronted by several pests and pathogens, thus reiterating interventions for their management. In this study, we report, the utility of a novel Arabidopsis miRNA173-directed trans-acting siRNA (tasiRNA)-based micro RNA-induced gene silencing (MIGS) strategy for the simultaneous management of cotton leaf curl disease (CLCuD), cotton leaf hopper (CLH; Amrasca biguttula biguttula) and root-knot nematode (RKN, Meloidogyne incognita). Cotton transgenics were developed with the MIGS construct targeting a total of 7 genes by an apical meristem-targeted in planta transformation strategy. Stable transgenics were selected using stringent selection pressure, molecular characterization and stress-specific bio-efficacy studies. We identified 8 superior events with 50-100% resistance against CLCuD, while reduction in the root-knot nematode multiplication factor in the range of 35-75% confirmed resistance to RKN. These transgenic cotton events were also detrimental to the growth and development of CLH, as only 43.3-62.5% of nymphs could survive. Based on the corroborating evidences obtained by all the bioefficacy analyses, 3 events viz., L-75-1, E-27-11, E-27-7 were found to be consistent in tackling the target pests. To the best of our knowledge, this report is the first of its kind demonstrating the possibility of combinatorial management of pests/diseases in cotton using MIGS approach. These identified events demonstrate immense utility of the strategy towards combinatorial stress management in cotton improvement programs.

Understanding Molecular Plant–Nematode Interactions to Develop Alternative Approaches for Nematode Control

Developing control measures of plant-parasitic nematodes (PPNs) rank high as they cause big crop losses globally. The growing awareness of numerous unsafe chemical nematicides and the defects found in their alternatives are calling for rational molecular control of the nematodes. This control focuses on using genetically based plant resistance and exploiting molecular mechanisms underlying plant–nematode interactions. Rapid and significant advances in molecular techniques such as high-quality genome sequencing, interfering RNA (RNAi) and gene editing can offer a better grasp of these interactions. Efficient tools and resources emanating from such interactions are highlighted herein while issues in using them are summarized. Their revision clearly indicates the dire need to further upgrade knowledge about the mechanisms involved in host-specific susceptibility/resistance mediated by PPN effectors, resistance genes, or quantitative trait loci to boost their effective and sustainable use in economically important plant species. Therefore, it is suggested herein to employ the impacts of these techniques on a case-by-case basis. This will allow us to track and optimize PPN control according to the actual variables. It would enable us to precisely fix the factors governing the gene functions and expressions and combine them with other PPN control tactics into integrated management.

Effectors of Root-Knot Nematodes: An Arsenal for Successful Parasitism

Root-knot nematodes (RKNs) are notorious plant-parasitic nematodes first recorded in 1855 in cucumber plants. They are microscopic, obligate endoparasites that cause severe losses in agriculture and horticulture. They evade plant immunity, hijack the plant cell cycle, and metabolism to modify healthy cells into giant cells (GCs) - RKN feeding sites. RKNs secrete various effector molecules which suppress the plant defence and tamper with plant cellular and molecular biology. These effectors originate mainly from sub-ventral and dorsal oesophageal glands. Recently, a few non-oesophageal gland secreted effectors have been discovered. Effectors are essential for the entry of RKNs in plants, subsequently formation and maintenance of the GCs during the parasitism. In the past two decades, advanced genomic and post-genomic techniques identified many effectors, out of which only a few are well characterized. In this review, we provide molecular and functional details of RKN effectors secreted during parasitism. We list the known effectors and pinpoint their molecular functions. Moreover, we attempt to provide a comprehensive insight into RKN effectors concerning their implications on overall plant and nematode biology. Since effectors are the primary and prime molecular weapons of RKNs to invade the plant, it is imperative to understand their intriguing and complex functions to design counter-strategies against RKN infection.

Identification, Characterization, and Evaluation of Nematophagous Fungal Species of Arthrobotrys and Tolypocladium for the Management of Meloidogyne incognita

Root-knot nematodes belonging to the genus Meloidogyne are agriculturally important pests, and biocontrol strategies offer safer alternatives for their management. In the present study, two fungal species from Indian soils were identified as Arthrobotrys thaumasia and Tolypocladium cylindrosporum based on morphological characteristics and further confirmed using molecular markers. In vitro evaluation of A. thaumasia against M. incognita and Caenorhabditis elegans showed 82 and 73% parasitism, respectively, whereas T. cylindrosporum gave 65.2 and 57.7% parasitism, respectively. Similarly, culture filtrates of A. thaumasia caused 57.7 and 53.7% mortality of M. incognita and C. elegans, respectively, whereas T. cylindrosporum caused higher mortality of 87.3 and 64%, respectively. Besides, greenhouse evaluation of both fungi against M. incognita infecting tomato significantly reduced nematode disease burden reflecting parasitic success measured as the total number of galls, egg masses, eggs per egg mass, and derived nematode multiplication factor. Application of A. thaumasia and T. cylindrosporum reduced nematode multiplication factor by 80 and 95%, respectively, compared with control. General metabolite profiling of tested fungi using gas chromatography–mass spectrometry and ultra-performance liquid chromatography–quadrupole/time of flight mass spectrometry reported for the first time here showed presence of various volatile and non-volatile compounds with nematicidal activity, viz., trimethyl-heptadiene, methyl-hexadecanol, dodecadienal, decane, terpendole E, dodecane, acetamido-6-anthraquinone, and hexadecanol. Also, other compounds such as undecane, dibutyl-disulfide, octadecenal, paganin, talathermophilin, dactylarin, tolypyridone A, tolypyridone B, pyridoxatin, and destruxin were identified, reported in the literature to possess antibacterial, antifungal, and insecticidal properties. This is the first report of the occurrence of both fungi from India and pioneer demonstration of T. cylindrosporum for root-knot nematode management.

Host-mediated RNAi for simultaneous silencing of different functional groups of genes in Meloidogyne incognita using fusion cassettes in Nicotiana tabacum

KEY MESSAGE

This study establishes possibility of combinatorial silencing of more than one functional gene for their efficacy against root-knot nematode, M. incognita. Root-knot nematodes (RKN) of the genus Meloidogyne are the key important plant parasitic nematodes (PPNs) in agricultural and horticultural crops worldwide. Among RKNs, M. incognita is the most notorious that demand exploration of novel strategies for their management. Due to its sustainable and target-specific nature, RNA interference (RNAi) has gained unprecedented importance to combat RKNs. However, based on the available genomic information and interaction studies, it can be presumed that RKNs are dynamic and not dependent on single genes for accomplishing a particular function. Therefore, it becomes extremely important to consider silencing of more than one gene to establish any synergistic or additive effect on nematode parasitism. In this direction, we have combined three effectors specific to subventral gland cells of M. incognita, Mi-msp1, Mi-msp16, Mi-msp20 as fusion cassettes-1 and two FMRFamide-like peptides, Mi-flp14, Mi-flp18, and Mi-msp20 as fusion cassettes-2 to establish their possible utility for M. incognita management. In vitro RNAi assay in tomato and adzuki bean using these two fusion gene negatively altered nematode behavior in terms of reduced attraction, invasion, development, and reproduction. Subsequently, Nicotiana tabacum plants were transformed with these two fusion gene hairpin RNA-expressing vectors (hpRNA), and characterized via PCR, qRT-PCR, and Southern blot hybridization. Production of siRNAs specific to Mi-flp18 and Mi-msp1 was also confirmed by Northern hybridization. Further, transgenic events expressing single copy insertions of hpRNA constructs of fusion 1 and fusion-2 conferred up to 85% reduction in M. incognita multiplication. Besides, expression quantification revealed a significant reduction in mRNA abundance of target genes (up to 1.8-fold) in M. incognita females extracted from transgenic plants, and provided additional evidence for successful gene silencing.

Pyramiding dsRNAs increases phytonematode tolerance in cotton plants

Host-derived suppression of nematode essential genes decreases reproduction of Meloidogyne incognita in cotton. Root-knot nematodes (RKN) represent one of the most damaging plant-parasitic nematode genera worldwide. RNAi-mediated suppression of essential nematode genes provides a novel biotechnological strategy for the development of sustainable pest-control methods. Here, we used a Host Induced Gene Silencing (HIGS) approach by stacking dsRNA sequences into a T-DNA construct to target three essential RKN genes: cysteine protease (Mi-cpl), isocitrate lyase (Mi-icl), and splicing factor (Mi-sf), called dsMinc1, driven by the pUceS8.3 constitutive soybean promoter. Transgenic dsMinc1-T₄ plants infected with Meloidogyne incognita showed a significant reduction in gall formation (57-64%) and egg masses production (58-67%), as well as in the estimated reproduction factor (60-78%), compared with the susceptible non-transgenic cultivar. Galls of the RNAi lines are smaller than the wild-type (WT) plants, whose root systems exhibited multiple well-developed root swellings. Transcript levels of the three RKN-targeted genes decreased 13- to 40-fold in nematodes from transgenic cotton galls, compared with those from control WT galls. Finally, the development of non-feeding males in transgenic plants was 2-6 times higher than in WT plants, indicating a stressful environment for nematode development after RKN gene silencing. Data strongly support that HIGS of essential RKN genes is an effective strategy to improve cotton plant tolerance. This study presents the first application of dsRNA sequences to target multiple genes to promote M. incognita tolerance in cotton without phenotypic penalty in transgenic plants.

RNA interference and crop protection against biotic stresses

RNA interference (RNAi) is a universal phenomenon of RNA silencing or gene silencing with broader implications in important physiological and developmental processes of most eukaryotes, including plants. Small RNA (sRNA) are the critical drivers of the RNAi machinery that ensures down-regulation of the target genes in a homology-dependent manner and includes small-interfering RNAs (siRNAs) and micro RNAs (miRNAs). Plant researchers across the globe have exploited the powerful technique of RNAi to execute targeted suppression of desired genes in important crop plants, with an intent to improve crop protection against pathogens and pests for sustainable crop production. Biotic stresses cause severe losses to the agricultural productivity leading to food insecurity for future generations. RNAi has majorly contributed towards the development of designer crops that are resilient towards the various biotic stresses such as viruses, bacteria, fungi, insect pests, and nematodes. This review summarizes the recent progress made in the RNAi-mediated strategies against these biotic stresses, along with new insights on the future directions in research involving RNAi for crop protection.

Biotechnological advances with applicability in potatoes for resistance against root-knot nematodes

Potato production is negatively affected by root-knot nematodes (Meloidogyne spp.). There are no commercially available potato cultivars that are resistant to root-knot nematodes. To reduce the reliance on chemical controls, genetic engineering for nematode resistance in potato shows promise. Genetically modified potatoes that silence a parasitism gene or that express toxic protease inhibitors display reduced nematode infections. Modifying potato immune responses may also offer new opportunities for nematode resistance in potato. Plant defense elicitors, including those secreted by modified bacteria, enhanced resistance against root-knot nematodes in potato. The use of transgenic bacteria as delivery vehicles of defense-related molecules presents several possibilities for sophisticated nematode management and because this does not involve transgenic plants, it may garner greater public acceptance.

Micro RNA-induced gene silencing strategy for the delivery of siRNAs targeting Meloidogyne incognita in a model plant Nicotiana benthamiana

BACKGROUND

Occurrence of multiple biotic stresses on crop plants result in drastic yield losses which may have severe impact on the food security. It is a challenge to design strategies for simultaneous management of these multiple stresses. Hence, establishment of innovative approaches that aid in their management is critical. Here, we have introgressed a micro RNA-induced gene silencing (MIGS) based combinatorial gene construct containing seven target gene sequences of cotton leaf curl disease (CLCuD), cotton leaf hopper (Amrasca biguttula biguttula), cotton whitefly (Bemisia tabaci) and root-knot nematode (Meloidogyne incognita).

RESULTS

Stable transgenic lines of Nicotiana benthamiana were generated with the T-DNA harboring Arabidopsis miR173 target site fused to fragments of Sec23 and ecdysone receptor (EcR) genes of cotton leaf hopper and cotton whitefly. It also contained C2/replication associated protein (C2/Rep) and C4 (movement protein) along with βC1 gene of betasatellite to target CLCuD, and two FMRFamide-like peptide (FLP) genes, Mi-flp14 and Mi-flp18 of M. incognita. These transgenic plants were assessed for the amenability of MIGS approach for pest control by efficacy evaluation against M. incognita. Results showed successful production of small interfering RNA (siRNA) through the tasiRNA (trans-acting siRNA) pathway in the transgenic plants corresponding to Mi-flp18 gene. Furthermore, we observed reduced Mi-flp14 and Mi-flp18 transcripts (up to 2.37 ± 0.12-fold) in females extracted from transgenic plants. The average number of galls, total endoparasites, egg masses and number of eggs per egg mass reduced were in the range 27-62%, 39-70%, 38-65% and 34-49%, respectively. More importantly, MIGS transgenic plants showed 80% reduction in the nematode multiplication factor (MF).

CONCLUSION

This study demonstrates successful validation of the MIGS approach in the model plant, N. benthamiana for efficacy against M. incognita, as a prelude to translation to cotton. © 2021 Society of Chemical Industry.

FMRFamide-Like Peptide 22 Influences the Head Movement, Host Finding, and Infection of Heterodera glycines

The FMRFamide-like peptides (FLPs) represent the largest family of nematode neuropeptides and are involved in multiple parasitic activities. The immunoreactivity to FMRFamide within the nervous system of Heterodera glycines, the most economically damaging parasite of soybean [Glycine max L. (Merr)], has been reported in previous research. However, the family of genes encoding FLPs of H. glycines were not identified and functionally characterized. In this study, an FLP encoding gene Hg-flp-22 was cloned from H. glycines, and its functional characterization was uncovered by using in vitro RNA interference and application of synthetic peptides. Bioinformatics analysis showed that flp-22 is widely expressed in multiple nematode species, where they encode the highly conserved KWMRFamide motifs. Quantitative real-time (qRT)-PCR results revealed that Hg-flp-22 was highly expressed in the infective second-stage juveniles (J2s) and adult males. Silencing of Hg-flp-22 resulted in the reduced movement of J2s to the host root and reduced penetration ability, as well as a reduction in their subsequent number of females. Behavior and infection assays demonstrated that application of synthetic peptides Hg-FLP-22b (TPQGKWMRFa) and Hg-FLP-22c (KMAIEGGKWVRFa) significantly increased the head movement frequency and host invasion abilities in H. glycines but not in Meloidogyne incognita. In addition, the number of H. glycines females on the host roots was found to be significantly higher in Hg-FLP-22b treated nematodes than the ddH₂O-treated control J2s. These results presented in this study elucidated that Hg-flp-22 plays a role in regulating locomotion and infection of H. glycines. This suggests the potential of FLP signaling as putative control targets for H. glycines in soybean production.