Targeting insect mitochondrial complex I for plant protection

Role of mitochondrial complex I genes in host plant expansion of Bactrocera tau (Tephritidae: Diptera) by CRISPR/Cas9 system

Host expansion facilitates tephritid flies to expand their ranges. Unraveling the mechanisms of host expansion will help to efficiently control these pests. Our previous works showed mitochondrial complex I genes Ndufs1, Ndufs3, and Ndufa7 being upregulated during host expansion of Bactrocera tau (Walker), one of the highly hazardous species of tephritids. However, their roles in the host expansion of B. tau remain unknown. Here, using clustered regularly interspaced short palindromic repeats (CRISPR) / CRISPR-associated nuclease 9 (Cas9) editing system for the first time, a stable homozygous Ndufa7 strain (Btndufa7-/-), heterozygous Ndufs1 (Btndufs1+/-), and Ndufs3 strains (Btndufs3+/-) were obtained from F3 generation of B. tau, after gene knockout. Reduced sizes of larvae and pupae of the Ndufa7 knockout strain were first observed. Notably, the mean values of fitness estimation (pupal numbers, single-pupal weight and emergence rate) and Ndufa7 gene expression in the Ndufa7 knockout strain were slightly reduced on 2 native hosts (summer squash and cucumber), while it sharply decreased on the novel host banana and the potential host pitaya, compared with those of the wild-type strain. Furthermore, the Ndufa7 knockout strain did not survive on the novel host guava. These results suggested that Ndufa7 disturbs the survival on native hosts, expansion to novel hosts, and further expansion to potential hosts of B. tau. Homozygous lethality occurred after the knockout of Ndufs1 or Ndufs3, suggesting that these 2 genes play a role in the early development of B. tau. This study revealed that Ndufa7 is a target gene for the management of tephritids and opens a new avenue for pest control research.

Inactivation of RPX1 in Arabidopsis confers resistance to Plutella xylostella through the accumulation of the homoterpene DMNT

The lepidopteran crop pest Plutella xylostella causes severe constraints on Brassica cultivation. Here, we report a novel role for RPX1 (resistance to P. xylostella) in resistance to this pest in Arabidopsis thaliana. The rpx1-1 mutant repels P. xylostella larvae, and feeding on the rpx1-1 mutant severely damages the peritrophic matrix structure in the midgut of the larvae, thereby negatively affecting larval growth and pupation. This resistance results from the accumulation of defence compounds, including the homoterpene (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), due to the upregulation of PENTACYCLIC TRITERPENE SYNTHASE 1 (PEN1), which encodes a key DMNT biosynthetic enzyme. P. xylostella infestation and wounding induce RPX1 protein degradation, which may confer a rapid response to insect infestation. RPX1 inactivation and PEN1 overexpression are not associated with negative trade-offs for plant growth but have much higher seed production than the wild-type in the presence of P. xylostella infestation. This study offers a new strategy for plant molecular breeding against P. xylostella.

Insecticidal activity of essential oils from American native plants against Aedes aegypti (Diptera: Culicidae): an introduction to their possible mechanism of action

Searching for new bioactive molecules to design insecticides is a complex process since pesticides should be highly selective, active against the vector, and bio-safe for humans. Aiming to find natural compounds for mosquito control, we evaluated the insecticidal activity of essential oils (EOs) from 20 American native plants against Aedes aegypti larvae using bioassay, biochemical, and in silico analyses. The highest larvicide activity was exhibited by EOs from Steiractinia aspera (LC₅₀ = 42.4 µg/mL), Turnera diffusa (LC₅₀ = 70.9 µg/mL), Piper aduncum (LC₅₀ = 55.8 µg/mL), Lippia origanoides (chemotype thymol/carvacrol) (LC₅₀ = 61.9 µg/mL), L. origanoides (chemotype carvacrol/thymol) (LC₅₀ = 59.8 µg/mL), Hyptis dilatata (LC₅₀ = 61.1 µg/mL), Elaphandra quinquenervis (LC₅₀ = 61.1 µg/mL), and Calycolpus moritzianus (LC₅₀ = 73.29 µg/mL) after 24 h. This biological activity may be related to the disruption of the electron transport chain through the mitochondrial protein complexes. We hypothesized that the observed EOs' effect is due to their major components, where computational approaches such as homology modeling and molecular docking may suggest the possible binding pose of secondary metabolites that inhibit the mitochondrial enzymes and acetylcholinesterase activity (AChE). Our results provided insights into the possible mechanism of action of EOs and their major compounds for new insecticide designs targeting the mitochondria and AChE activity in A. aegypti for effective and safe insecticide.

Control of a sap-sucking insect pest by plastid-mediated RNA interference

Expression of double-stranded RNAs in plastids offers great potential for the efficient control of chewing insects. However, many insect pests do not consume plant tissue but rather feed on the host plant by sucking sap from the vascular system. Whether or not plastid-mediated RNA interference (RNAi) can be employed to control sap-sucking insects is unknown. Here, we show that five species of sap-sucking hemipteran insects acquire plastid RNA upon feeding on plants. We generated both nuclear transgenic and transplastomic tobacco plants expressing double-stranded RNAs targeting the MpDhc64C gene, a newly identified efficient target gene of RNAi whose silencing causes lethality to the green peach aphid Myzus persicae. In a whole-plant bioassay, transplastomic plants exhibited significant resistance to aphids, as evidenced by reduced insect survival, impaired fecundity, and decreased weight of survivors. The protective effect was comparable with that conferred by the best-performing nuclear transgenic plants. We found that the proportion of aphids on mature leaves of transplastomic plants was significantly lower compared with that of nuclear transgenic plants. When aphids were allowed to infest only the mature leaves, transplastomic plants grew significantly faster and were overall better protected from the pest compared with nuclear transgenic plants. When monitored by electrical-penetration-graph analyses and aphid avoidance response experiments, the insects displayed remarkable alterations in feeding behavior, which was different in nuclear transgenic and transplastomic plants, likely reflecting specific avoidance strategies to toxic RNA molecules. Taken together, our study demonstrates that plastid-mediated RNAi provides an efficient strategy for controlling at least some sap-sucking insect pests, even though there is most likely no or only very little chloroplast RNA in the sap.

Resistance to RNA interference by plant-derived double-stranded RNAs but not plant-derived short interfering RNAs in Helicoverpa armigera

Plant-mediated RNA interference (RNAi) has emerged as a promising technology for pest control through expression of double-stranded RNAs (dsRNAs) targeted against essential insect genes. However, little is known about the underlying molecular mechanisms and whether long dsRNA or short interfering RNAs (siRNAs) are the effective triggers of the RNAi response. Here we generated transplastomic and nuclear transgenic tobacco plants expressing dsRNA against the Helicoverpa armigera ATPaseH gene. We showed that expression of long dsRNA of HaATPaseH was at least three orders of magnitude higher in transplastomic plants than in transgenic plants. HaATPaseH-derived siRNAs are absent from transplastomic plants, while they are abundant in transgenic plants. Feeding transgenic plants to H. armigera larvae reduced gene expression of HaATPaseH and delayed growth. Surprisingly, no effect of transplastomic plants on insect growth was observed, despite efficient dsRNA expression in plastids. Furthermore, we found that dsRNA ingested by H. armigera feeding on transplastomic plants was rapidly degraded in the intestinal fluid. In contrast, siRNAs are relatively stable in the digestive system. These results suggest that plant-derived siRNAs may be more effective triggers of RNAi in Lepidoptera than dsRNAs, which will aid the optimization of the strategies for plant-mediated RNAi to pest control.

Efficient control of western flower thrips by plastid-mediated RNA interference

Plastid-mediated RNA interference (PM-RNAi) has emerged as a promising strategy for pest control. Expression from the plastid genome of stable double-stranded RNAs (dsRNAs) targeted against essential insect genes can effectively control some herbivorous beetles, but little is known about the efficacy of the transplastomic approach in other groups of pest insects, especially nonchewing insects that do not consume large amounts of leaf material. Here we have investigated the susceptibility of the western flower thrip (WFT, Frankliniella occidentalis), a notorious pest in greenhouses and open fields, to PM-RNAi. We show that WFTs ingest chloroplasts and take up plastid-expressed dsRNAs. We generated a series of transplastomic tobacco plants expressing dsRNAs and hairpin RNAs (hpRNAs) targeted against four essential WFT genes. Unexpectedly, we discovered plastid genome instability in transplastomic plants expressing hpRNAs, suggesting that dsRNA cassettes are preferable over hpRNA cassettes when designing PM-RNAi strategies. Feeding studies revealed that, unlike nuclear transgenic plants, transplastomic plants induced a potent RNAi response in WFTs, causing efficient suppression of the targeted genes and high insect mortality. Our study extends the application range of PM-RNAi technology to an important group of nonchewing insects, reveals design principles for the construction of dsRNA-expressing transplastomic plants, and provides an efficient approach to control one of the toughest insect pests in agriculture and horticulture.

RNAi technology for plant protection and its application in wheat

The RNAi technology takes advantage of the intrinsic RNA interference (RNAi) mechanism that exists in nearly all eukaryotes in which target mRNAs are degraded or functionally suppressed. Significant progress has been made in recent years where RNAi technology is applied to several crops and economic plants for protection against diseases like fungi, pests, and nematode. RNAi technology is also applied in controlling pathogen damages in wheat, one of the most important crops in the world. In this review, we first give a brief introduction of the RNAi technology and the underneath mechanism. We then review the recent progress of its utilization in crops, particular wheat. Finally, we discuss the existing challenges and prospect future development of this technology in crop protection.

Cloning and RNAi-mediated three lethal genes that can be potentially used for Chilo suppressalis (Lepidoptera: Crambidae) management

RNA interference (RNAi) has gained attention in recent years as a viable pest control strategy. Here, RNAi assays were performed to screen the potential functionality of genes in Chilo suppressalis, a serious pest of rice, and to determine their potential for developing a highly targeted molecular control approach. Potential homologs of NADH dehydrogenase (ND), glycerol 3-phosphate dehydrogenase (GPDH) and male specific lethal 3 (MSL3) were cloned from C. suppressalis, and their spatiotemporal gene expression evaluated. The expression of all three genes was higher in the pupal and adult stages than the larval stages and largely higher in the larval head compared to other tissues. Newly hatched larvae exhibited high mortalities and suppressed growth when fed bacteria producing double-stranded RNAs (dsRNAs) corresponding to the three target genes. This study provides insights into the function of ND, GPDH and MSL3 during C. suppressalis larval development and suggests that all may be candidate gene targets for C. suppressalis pest management.

NDUFV2 pseudogene (NDUFV2P1) contributes to mitochondrial complex I deficits in schizophrenia

Mitochondria together with other cellular components maintain a constant crosstalk, modulating transcriptional and posttranslational processes. We and others demonstrated mitochondrial multifaceted dysfunction in schizophrenia, with aberrant complex I (CoI) as a major cause. Here we show deficits in CoI activity and homeostasis in schizophrenia-derived cell lines. Focusing on a core CoI subunit, NDUFV2, one of the most severely affected subunits in schizophrenia, we observed reduced protein level and functioning, with no change in mRNA transcripts. We further show that NDUFV2 pseudogene (NDUFV2P1) expression is increased in schizophrenia-derived cells and in postmortem brain specimens. In schizophrenia and controls pooled samples, NDUFV2P1 level demonstrated a significant inverse correlation with NDUFV2 pre- and matured protein level and with CoI-driven cellular respiration. Our data suggest a role for a pseudogene in its parent-gene regulation and possibly in CoI dysfunction in schizophrenia. The abnormal expression of the pseudogene may be one element of a vicious circle in which CoI deficits lead to mitochondrial dysfunction potentially affecting genome-wide regulation of gene expression, including the expression of pseudogenes.

Insect-Resistant Genetically Engineered Crops in China: Development, Application, and Prospects for Use

With 20% of the world's population but just 7% of the arable land, China has invested heavily in crop biotechnology to increase agricultural productivity. We examine research on insect-resistant genetically engineered (IRGE) crops in China, including strategies to promote their sustainable use. IRGE cotton, rice, and corn lines have been developed and proven efficacious for controlling lepidopteran crop pests. Ecological impact studies have demonstrated conservation of natural enemies of crop pests and halo suppression of crop-pest populations on a local scale. Economic, social, and human health effects are largely positive and, in the case of Bt cotton, have proven sustainable over 20 years of commercial production. Wider adoption of IRGE crops in China is constrained by relatively limited innovation capacity, public misperception, and regulatory inaction, suggesting the need for further financial investment in innovation and greater scientific engagement with the public. The Chinese experience with Bt cotton might inform adoption of other Bt crops in China and other developing countries.

Cross-Kingdom Small RNAs Among Animals, Plants and Microbes

Small RNAs (sRNAs), a class of regulatory non-coding RNAs around 20~30-nt long, including small interfering RNAs (siRNAs) and microRNAs (miRNAs), are critical regulators of gene expression. Recently, accumulating evidence indicates that sRNAs can be transferred not only within cells and tissues of individual organisms, but also across different eukaryotic species, serving as a bond connecting the animal, plant, and microbial worlds. In this review, we summarize the results from recent studies on cross-kingdom sRNA communication. We not only review the horizontal transfer of sRNAs among animals, plants and microbes, but also discuss the mechanism of RNA interference (RNAi) signal transmission via cross-kingdom sRNAs. We also compare the advantages of host-induced gene silencing (HIGS) and spray-induced gene silencing (SIGS) technology and look forward to their applicable prospects in controlling fungal diseases.

Milk MicroRNAs in Health and Disease

MicroRNAs are small noncoding RNAs responsible for regulating 40% to 60% of gene expression at the posttranscriptional level. The discovery of circulating microRNAs in several biological fluids opened the path for their study as biomarkers and long-range cell-to-cell communication mediators. Their transfer between individuals in the case of blood transfusion, for example, and their high enrichment in milk have sparked the interest for microRNA transfer through diet, especially from mothers to infants during breastfeeding. The extension of such paradigm led to the study of milk microRNAs in the case of cow or goat milk consumption in adults. Here we provide a comprehensive critical review of the key findings surrounding milk microRNAs in human, cow, and goat milk among other species. We discuss the data on their biological properties, their use as disease biomarkers, their transfer between individuals or species, and their putative or verified functions in health and disease of infants and adult consumers. This work is based on all the literature available and integrates all the results, theories, debates, and validation studies available so far on milk microRNAs and related areas of investigations. We critically discuss the limitations and outline future aspects and avenues to explore in this rapidly growing field of research that could impact public health through infant milk formulations or new therapies. We hope that this comprehensive review of the literature will provide insight for all teams investigating milk RNAs' biological activities and help ensure the quality of future reports.

Overexpression of ghr-miR166b generates resistance against Bemisia tabaci infestation in Gossypium hirsutum plants

MAIN CONCLUSION

In silico identified Gossypium hirsutum ghr-miR166b shows multi-compatible targets in mitochondrial ATP synthase of Bemisia tabaci. Its overexpression in planta has the potential to act as a biopesticide in reducing B. tabaci population, and consequently the spread of whitefly-transmitted plant viruses. Whiteflies (B. tabaci) are hemipterous insects that act as a vector to transmit plant viruses causing enormous losses to the plants. In the present study, G. hirsutum-encoded miRNAs targeting expressed sequence tags (ESTs) of B. tabaci, based on sequence complimentarity and miRNA-target mRNA thermodynamics, were in silico identified. Out of 108 G. hirsutum miRNAs, 55 targeted the protein encoding ESTs. Among them, ghr-miR166b was selected owing to its intrinsic affinity for ATP synthase. Its functional role was validated following expression of ghr-MIR166b (precursor) sequence in G. hirsutum cv. HS6 plants through Agrobacterium-mediated transformation. Total of seven independent transformed (T0) G. hirsutum lines were obtained. The transcript level of ghr-MIR166b in the transgenic lines was observed to be 2.0- to 17-fold higher as compared to non-transformed plants. Northern-blot analysis of small RNAs isolated from the transgenic plants confirmed the presence of the ghr-miR166b. After feeding on the leaves of transgenic line (HS6-166-30) having highest level of ghr-miR166b expression, B. tabaci population was reduced up to 91% as compared to non-transformed leaves. Further, in the whole plant assay, a maximum of 78% B. tabaci mortality was observed in the same line, while there was an increase in B. tabaci population on the non-transformed plants. Our results revealed that ghr-miR166b supposedly targeting ATP synthase gene of B. tabaci, and subsequently its overexpression in planta has potential to act as biopesticide for reducing B. tabaci population and consequently spread of whitefly transmitted viruses.

Transcriptome analysis of three cotton pests reveals features of gene expressions in the mesophyll feeder Apolygus lucorum

The green mirid bug Apolygus lucorum is an agricultural pest that is known to cause damage to more than 150 plant species. Here, we report the transcriptomes of A. lucorum at three different developmental stages (the second and fifth instar nymphs and adults). A total of 98,236 unigenes with an average length of 1,335 nt was obtained, of which 50,640 were annotated, including those encoding digestive enzymes and cytochrome P450s. Comparisons with cotton bollworm and cotton aphid transcriptomes revealed distinct features of A. lucorum as a mesophyll feeder. The gene expression dynamics varied during development from young nymphs to adults. The high-quality transcriptome data and the gene expression dynamics reported here provide valuable data for a more comprehensive understanding of the physiology and development of mirid bugs, and for mining targets for their control.

Diet-derived microRNAs: unicorn or silver bullet?

In ancient lore, a bullet cast from silver is the only effective weapon against monsters. The uptake of active diet-derived microRNAs (miRNAs) in consumers may be the silver bullet long sought after in nutrition and oral therapeutics. However, the majority of scientists consider the transfer and regulation of consumer’s gene activity by these diet-derived miRNAs to be a fantasy akin to spotting a unicorn. Nevertheless, groups like Dr. Chen-Yu Zhang’s lab in Nanjing University have stockpiled breathtaking amounts of data to shoot down these naysayers. Meanwhile, Dr. Ken Witwer at John Hopkins has steadfastly cautioned the field to beware of fallacies caused by contamination, technical artifacts, and confirmation bias. Here, Dr. Witwer and Dr. Zhang share their realities of dietary miRNAs by answering five questions related to this controversial field.

New Insight into Inter-kingdom Communication: Horizontal Transfer of Mobile Small RNAs

Small RNAs (sRNAs), including small interfering RNAs (siRNAs) and microRNAs (miRNAs), are conventionally regarded as critical molecular regulators of various intracellular processes. However, recent accumulating evidence indicates that sRNAs can be transferred within cells and tissues and even across species. In plants, nematodes and microbes, these mobile sRNAs can mediate inter-kingdom communication, environmental sensing, gene expression regulation, host-parasite defense and many other biological functions. Strikingly, a recent study by our group suggested that ingested plant miRNAs are transferred to blood, accumulate in tissues and regulate transcripts in consuming animals. While our and other independent groups’ subsequent studies further explored the emerging field of sRNA-mediated crosstalk between species, some groups reported negative results and questioned its general applicability. Thus, further studies carefully evaluating the horizontal transfer of exogenous sRNAs and its potential biological functions are urgently required. Here, we review the current state of knowledge in the field of the horizontal transfer of mobile sRNAs, suggest its future directions and key points for examination and discuss its potential mechanisms and application prospects in nutrition, agriculture and medicine.