Unveiling sugarcane defense response to Mythimna separata herbivory by a combination of transcriptome and metabolic analyses

Bioactivity of silverleaf nightshade (Solanum elaeagnifolium Cav.) berries parts against Galleria mellonella and Erwinia carotovora and LC-MS chemical profile of its potential extract

Natural products received much attention as an environmentally beneficial solution for pest management. Therefore, the extracts of invasive silverleaf nightshade (Solanum elaeagnifolium Cav.) weeds using their berries parts (seeds, peels and mucilage) supported by bioassay-guided fractionation were tested against both the greater wax moth (Galleria mellonella) and Erwinia carotovora pv. carotovora causes of the blackleg of potatoes. The seeds and peels of S. elaeagnifolium were successively extracted by maceration using dichloromethane (DCM), ethyl acetate (EtOAc), and ethanol (EtOH), respectively. While, its mucilage was extracted using EtOAc. The successive EtOH extract of the plant seeds had promising inhibition efficacy and the best minimal inhibition concentration (MIC) of 50 µg/ml against E. Carotovora amongst other extracts (DCM and EtOAc of the plant berries parts). Depending on dose response activity, EtOH extract had G. mellonella larval mortality and pupal duration rates (LC50; 198.30 and LC95; 1294.73 µg/ml), respectively. Additionally, this EtOH extract of seeds was fractionated using preparative TLC to three characteristic bands. The insecticidal and bacterial activities of these isolated bands (SEA, SEB, and SEC) were evaluated at a dose of 100 µg/ml, causing mortality by 48.48, 62.63 and 92.93% (G. mellonella larvae) and inhibition by 15.22, 0.00 and 31.66 mm (E. carotovora), respectively. Moreover, the separated major three bands were tentatively identified using LC-ESI-MS analysis revealing the presence of two phenolic acids; chlorogenic acid (SEA) and dicaffeoyl quinic acid (SEB) in addition to one steroidal saponin (SEC) annotated as borassoside E or yamoscin. Finally, the plant seeds' successive EtOH extract as well as its active constituents, exhibited potential broad-spectrum activity and the ability to participate in future pest management initiatives. A field study is also recommended to validate its bio-efficacy against selected pests and to develop its formulations.

Genetic Engineering for Enhancing Sugarcane Tolerance to Biotic and Abiotic Stresses

Sugarcane, a vital cash crop, contributes significantly to the world's sugar supply and raw materials for biofuel production, playing a significant role in the global sugar industry. However, sustainable productivity is severely hampered by biotic and abiotic stressors. Genetic engineering has been used to transfer useful genes into sugarcane plants to improve desirable traits and has emerged as a basic and applied research method to maintain growth and productivity under different adverse environmental conditions. However, the use of transgenic approaches remains contentious and requires rigorous experimental methods to address biosafety challenges. Clustered regularly interspaced short palindromic repeat (CRISPR) mediated genome editing technology is growing rapidly and may revolutionize sugarcane production. This review aims to explore innovative genetic engineering techniques and their successful application in developing sugarcane cultivars with enhanced resistance to biotic and abiotic stresses to produce superior sugarcane cultivars.

A ScWIP5 gene confers fall armyworm resistance by reducing digestive enzyme activities in sugarcane

BACKGROUND

The fall armyworm, Spodoptera frugiperda, is one of the most dangerous pests to various crops. As the most crucial sugar crop, sugarcane is also constantly threatened by these pests. Plant wound-induced proteinase inhibitors (WIP) are natural defense proteins that play important roles in the defense system against insect attack. Breeding for resistance would be the best way to improve the variety characteristics and productivity of sugarcane. Screening and verification for potential plant endogenous insect-resistant genes would greatly improve the insect-resistant breeding progress of sugarcane.

RESULTS

A sugarcane WIP5 gene (ScWIP5) was up-regulated 536 times after insect feeding treatment on previous published transcriptome databases. ScWIP5 was then cloned and its potential role in sugarcane resistance to fall armyworm evaluated by construction of transgenic Nicotiana benthamiana. The toxicity of ScWIP5 transgenic N. benthamiana to fall armyworm showed lower weight gain and higher mortality compared to wild-type N. benthamiana feeding group. Furthermore, the concentration of JA and NbAOC, NbAOS, and NbLOX from the Jasmin acid biosynthesis pathway was significantly induced in ScWIP5 transgenic N. benthamiana compared to the control. In addition, digestive enzyme actives from the insect gut were also evaluated, and trypsin and cathepsin were significantly lower in insects fed with ScWIP5 transgenic N. benthamiana.

CONCLUSION

These results indicate that ScWIP5 might enhance insect resistance by increasing JA signal transduction processes and reducing insect digestive enzyme activities, thus impacting insect growth and development. © 2023 Society of Chemical Industry.

Chromosome level genome assembly of oriental armyworm Mythimna separata

The oriental armyworm, Mythimna separata, is an extremely destructive polyphagous pest with a broad host range that seriously threatens the safety of agricultural production. Here, a high-quality chromosome-level genome was assembled using Illumina, PacBio HiFi long sequencing, and Hi-C scaffolding technologies. The genome size was 706.30 Mb with a contig N50 of 22.08 Mb, and 99.2% of the assembled sequences were anchored to 31 chromosomes. In addition, 20,375 protein-coding genes and 258.68 Mb transposable elements were identified. The chromosome-level genome assembly of M. separata provides a significant genetic resource for future studies of this insect and contributes to the development of management strategies.

Toxicity, baseline of susceptibility, detoxifying mechanism and sublethal effects of chlorogenic acid, a potential botanical insecticide, on Bemisia tabaci

Bemisia tabaci is a threat to agriculture worldwide because of its potential to cause devastating damage to crops. Chlorogenic acid is a bioactive pesticidal phytochemical agent against various insect pests. We here determined the susceptibility of a laboratory strain of B. tabaci to chlorogenic acid and other popular insecticides, and the susceptibility of several field-collected populations to chlorogenic acid. Also, cross-resistance to four common insecticides was measured. Chlorogenic acid had the highest toxicity of all tested insecticides, and all the field-collected populations were susceptible to chlorogenic acid, and little cross-resistance was detected between chlorogenic acid and the other tested insecticides. Furthermore, analysis of enzyme activities and expression of P450 genes in B. tabaci after treatment with LC₅₀ of chlorogenic acid suggested that enhanced P450 activity could be involved in chlorogenic acid detoxification. We subsequently evaluated sublethal effects of chlorogenic acid, and found that treatment with LC₂₅ of chlorogenic acid prolonged duration of two developmental stages, reduced fecundity, and decreased survival rates of treated B. tabaci compared to untreated insects. Overall, these findings demonstrate strong toxicity and significant sublethal effects of chlorogenic acid on B. tabaci, and suggest that overexpression of P450 genes may be associated with chlorogenic acid detoxification.

Physiological and Environmental Influences on Wingbeat Frequency of Oriental Armyworm, Mythimna separata (Lepidoptera: Noctuidae)

The oriental armyworm, Mythimna separata (Walker, 1865) (Lepidoptera: Noctuidae), is a serious global migratory insect pest of grain crops. Although its migratory biology has been studied for a long history, the factors affecting wingbeat frequency (WBF), which is closely related to the flight activity of the insect, remain unclear. In this study, the WBFs of both cultured and migrating moths were tested under different conditions in the laboratory using a stroboscope. The results indicated that age and mating status significantly influenced WBF. One day old adults had the lowest WBF, and unmated females had a significantly higher WBF than that of mated females. In general, the WBF of males was significantly higher than that of female individuals. The WBF decreased gradually with increasing environmental humidity, and WBF had a significant negative binomial regression relationship with temperature change. The WBF of moths that fed on hydromel was much higher than those of the controls that fed on water or without diet. However, wind speed and air pressure had no significant effects on the moth WBF in the test environments. These findings provide a deeper understanding of factors that affect flight ability in M. separata, which will be helpful for developing a regional migratory monitoring and warning system of the pest, such as identifying target insect species based on the WBF from radar observation.

Integrated Transcriptome and Metabolome Analysis to Identify Sugarcane Gene Defense against Fall Armyworm (Spodoptera frugiperda) Herbivory

Sugarcane is the most important sugar crop, contributing ≥80% to total sugar production around the world. Spodoptera frugiperda is one of the main pests of sugarcane, potentially causing severe yield and sugar loss. The identification of key defense factors against S. frugiperda herbivory can provide targets for improving sugarcane resistance to insect pests by molecular breeding. In this work, we used one of the main sugarcane pests, S. frugiperda, as the tested insect to attack sugarcane. Integrated transcriptome and metabolomic analyses were performed to explore the changes in gene expression and metabolic processes that occurred in sugarcane leaf after continuous herbivory by S. frugiperda larvae for 72 h. The transcriptome analysis demonstrated that sugarcane pest herbivory enhanced several herbivory-induced responses, including carbohydrate metabolism, secondary metabolites and amino acid metabolism, plant hormone signaling transduction, pathogen responses, and transcription factors. Further metabolome analysis verified the inducement of specific metabolites of amino acids and secondary metabolites by insect herbivory. Finally, association analysis of the transcriptome and metabolome by the Pearson correlation coefficient method brought into focus the target defense genes against insect herbivory in sugarcane. These genes include amidase and lipoxygenase in amino acid metabolism, peroxidase in phenylpropanoid biosynthesis, and pathogenesis-related protein 1 in plant hormone signal transduction. A putative regulatory model was proposed to illustrate the sugarcane defense mechanism against insect attack. This work will accelerate the dissection of the mechanism underlying insect herbivory in sugarcane and provide targets for improving sugarcane variety resistance to insect herbivory by molecular breeding.

The insecticidal effect of the botanical insecticide chlorogenic acid on Mythimna separata (Walker) is related to changes in MsCYP450 gene expression

The oriental armyworm Mythimna separata (Walker) (Lepidoptera: Noctuidae) can feed on the leaves of many crops, resulting in vast areas of damage and severe losses. Therefore, this insect has become a significant agricultural pest in north Asia. In this study, we fed 3^rd instar larvae with artificial diets containing different concentrations of chlorogenic acid and found a significant lethal effect and the mortality increased with increasing chlorogenic acid concentration. Next, we measured the sublethal effect of chlorogenic acid at LC₂₀ on the growth and development of M. separata larvae. The durations of the 4^th and 5^th instar were longer than those of the control group (prolonged by 0.8 and 0.6 days, respectively), and the 6^th instar was shorter (by 1.1 days). The total survival rate, pupation rate, eclosion rate, sex ratio, and oviposition amount in the LC₂₀ chlorogenic acid-treated group were significantly lower than those in the control group. Furthermore, transcriptome analysis of 3^rd instar larvae fed various concentrations of chlorogenic acid revealed that several MsCYP450 genes were significantly up-regulated, and this finding was further validated by qRT-PCR. In addition, various concentrations of chlorogenic acid and different treatment times significantly affected the enzyme activity of CYP450 in 3^rd instar larvae. Importantly, dietary ingestion of dsMsCYP450 significantly reduced the mRNA level of MsCYP450 genes and increased mortality in the presence of chlorogenic acid. Our results revealed that MsCYP6B6, MsCYP321A7, and MsCYP6B7-like play an essential role in the detoxification of chlorogenic acid by M. separata. This study provides evidence of control effect by botanical insecticide chlorogenic acid on M. separata, and potential detoxification mechanism mediated by P450 of botanical insecticide in arthropods.

Deciphering of Pod Borer [Helicoverpa armigera (Hübner)] Resistance in Cajanus platycarpus (Benth.) Offers Novel Insights on the Reprogramming and Role of Flavonoid Biosynthesis Pathway

Management of pod borer, Helicoverpa armigera in pigeonpea (Cajanus cajan L.), an important legume crop, has been a pertinent endeavor globally. As with other crops, wild relatives of pigeonpea are bestowed with various resistance traits that include the ability to deter the H. armigera. Understanding the molecular basis of pod borer resistance could provide useful leads for the management of this notorious herbivore. Earlier studies by our group in deciphering the resistance response to herbivory through multiomics approaches in the pigeonpea wild relative, Cajanus platycarpus, divulged the involvement of the flavonoid biosynthesis pathway, speculating an active chemical response of the wild relative to herbivory. The present study is a deeper understanding of the chemical basis of pod borer (H. armigera) resistance in, C. platycarpus, with focus on the flavonoid biosynthesis pathway. To substantiate, quantification of transcripts in H. armigera-challenged C. platycarpus (8 h, 24 h, 48 h, 96 h) showed dynamic upregulation (up to 11-fold) of pivotal pathway genes such as chalcone synthase, dihydroflavonol-4-reductase, flavonoid-3'5'-hydroxylase, flavonol synthase, leucoanthocyanidin reductase, and anthocyanidin synthase. Targeted LC-MS analyses demonstrated a concomitant increase (up to 4-fold) in naringenin, kaempferol, quercetin, delphinidin, cyanidin, epigallocatechin, and epicatechin-3-gallate. Interestingly, H. armigera diet overlaid with the over-produced flavonoids (100 ppm) showed deleterious effects on growth leading to a prolonged larval period demonstrating noteworthy coherence between over-accumulation of pathway transcripts/metabolites. The study depicts novel evidence for the directed metabolic reprogramming of the flavonoid biosynthesis pathway in the wild relative to pod borer; plant metabolic potential is worth exploiting for pest management.