Role of jasmonate signaling in rice resistance to the leaf folder Cnaphalocrocis medinalis

The jasmonate pathway and water loss in rice leaves induced by a stem-borer inhibit leaf-feeder growth

Plant-mediated interactions between herbivores play an important role in regulating the composition of herbivore community. The fall armyworm (FAW), Spodoptera frugiperda, which has become one of the most serious pests on corn in China since it invaded in 2018, has been found feeding rice in the field. However, how FAW interacts with native rice insect pests remains largely unknown. Here, we investigated the interaction between FAW and a resident herbivore, striped stem borer (SSB, Chilo suppressalis) on rice. The infestation of rice leaf sheaths (LSs) by SSB larvae systemically enhanced the level of jasmonic acid (JA), abscisic acid (ABA), and trypsin proteinase inhibitors (TPIs), reduced relative water content (RWC) in leaf blades (LBs), and suppressed the growth of FAW larvae. In contrast, because FAW larvae infested LBs and did not affect defence responses in LSs, they did not influence the performance of SSB larvae. Using different mutants, together with bioassays and chemical analysis, we revealed that SSB-induced suppression of FAW larvae growth depended on both the SSB-activated JA pathway and RWC in LBs, whereas the ABA pathway activated by SSB larvae promoted the growth of FAW larvae by impeding water loss. These results provide new insights into mechanisms underlying plant-mediated interactions between herbivores.

Active defense strategies for invasive plants may alter the distribution pattern of pests in the invaded area

Introduction

In the invaded areas, it is believed that invasive species reduce their investment in defense due to the absence of natural enemies.

Methods

By field investigation and a series of laboratory assays, This study explored the defense strategies of invasive plants.

Results

Field investigation indicated that invasive plants have a antifeedant effect on herbivorous pests, and the distribution frequency of wormholes of native plants shows a peak at a distance of 2-3 m from the invasive species. The feeding preference experiment conducted with two generalist herbivorous insects (native insect Spodoptera litura and invasive insect Spodoptera frugiperda) showed that the invasive plants have a stronger antifeedant effect than native plants. By analyzing the content of secondary metabolites in the leaves of three invasive plants (Sphagneticola trilobata, Mikania micrantha, Ipomoea cairica) and three native plants (Ipomoea nil, Paederia foetida, Polygonum chinense), the leaves of invasive plants had higher concentrations of substances associated with defenses, including total phenols, flavonoids, jasmonic acid, tannin, H2O2, and total antioxidant capacity (TAC), and lower soluble protein concentrations than native plants. After leaf damage, compared to native plants, the leaves of invasive plants showed an overall increase in substances associated with defense, except for soluble sugar.

Discussion

These results suggest that invasive plants maintain active defense strategies in invaded areas, leading to changes in the distribution patterns of herbivorous insects in a manner that facilitates invasion.

Integrated Omics Analysis Reveals Key Pathways in Cotton Defense against Mirid Bug (Adelphocoris suturalis Jakovlev) Feeding

The recent dominance of Adelphocoris suturalis Jakovlev as the primary cotton field pest in Bt-cotton-cultivated areas has generated significant interest in cotton pest control research. This study addresses the limited understanding of cotton defense mechanisms triggered by A. suturalis feeding. Utilizing LC-QTOF-MS, we analyzed cotton metabolomic changes induced by A. suturalis, and identified 496 differential positive ions (374 upregulated, 122 downregulated) across 11 categories, such as terpenoids, alkaloids, phenylpropanoids, flavonoids, isoflavones, etc. Subsequent iTRAQ-LC-MS/MS analysis of the cotton proteome revealed 1569 differential proteins enriched in 35 metabolic pathways. Integrated metabolome and proteome analysis highlighted significant upregulation of 17 (89%) proteases in the α-linolenic acid (ALA) metabolism pathway, concomitant with a significant increase in 14 (88%) associated metabolites. Conversely, 19 (73%) proteases in the fructose and mannose biosynthesis pathway were downregulated, with 7 (27%) upregulated proteases corresponding to the downregulation of 8 pathway-associated metabolites. Expression analysis of key regulators in the ALA pathway, including allene oxidase synthase (AOS), phospholipase A (PLA), allene oxidative cyclase (AOC), and 12-oxophytodienoate reductase3 (OPR3), demonstrated significant responses to A. suturalis feeding. Finally, this study pioneers the exploration of molecular mechanisms in the plant-insect relationship, thereby offering insights into potential novel control strategies against this cotton pest.

Rice responds to Spodoptera frugiperda infestation via epigenetic regulation of H3K9ac in the jasmonic acid signaling and phenylpropanoid biosynthesis pathways

KEY MESSAGE

This study provided important insights into the complex epigenetic regulatory of H3K9ac-modified genes involved in the jasmonic acid signaling and phenylpropanoid biosynthesis pathways of rice in response to Spodoptera frugiperda infestation. Physiological and molecular mechanisms underlying plant responses to insect herbivores have been well studied, while epigenetic modifications such as histone acetylation and their potential regulation at the genomic level of hidden genes remain largely unknown. Histone 3 lysine 9 acetylation (H3K9ac) is an epigenetic marker widely distributed in plants that can activate gene transcription. In this study, we provided the genome-wide profiles of H3K9ac in rice (Oryza sativa) infested by fall armyworm (Spodoptera frugiperda, FAW) using CUT&Tag-seq and RNA-seq. There were 3269 and 4609 up-regulated genes identified in plants infested by FAW larvae for 3 h and 12 h, respectively, which were mainly enriched in alpha-linolenic acid and phenylpropanoid pathways according to transcriptomic analysis. In addition, CUT&Tag-seq analysis revealed increased H3K9ac in FAW-infested plants, and there were 422 and 543 up-regulated genes enriched with H3K9ac observed at 3 h and 12 h after FAW feeding, respectively. Genes with increased H3K9ac were mainly enriched in the transcription start site (TSS), suggesting that H3K9ac is related to gene transcription. Integrative analysis of both RNA-seq and CUT&Tag-seq data showed that up-expressed genes with H3K9ac enrichment were mainly involved in the jasmonic acid (JA) and phenylpropanoid pathways. Particularly, two spermidine hydroxycinnamoyl transferase genes SHT1 and SHT2 involved in phenolamide biosynthesis were highly modified by H3K9ac in FAW-infested plants. Furthermore, the Ossht1 and Ossht2 transgenic lines exhibited decreased resistance against FAW larvae. Our findings suggest that rice responds to insect herbivory via H3K9ac epigenetic regulation in the JA signaling and phenolamide biosynthesis pathways.

Defense Responses of Different Rice Varieties Affect Growth Performance and Food Utilization of Cnaphalocrocis medinalis Larvae

Rice leaf folder, Cnaphalocrocis medinalis (Guenée), is one of the most serious pests on rice. At present, chemical control is the main method for controlling this pest. However, the indiscriminate use of chemical insecticides has non-target effects and may cause environmental pollution. Besides, leaf curling behavior by C. medinalis may indirectly reduce the efficacy of chemical spray. Therefore, it is crucial to cultivate efficient rice varieties resistant to this pest. Previous studies have found that three different rice varieties, Zhongzao39 (ZZ39), Xiushui134 (XS134), and Yongyou1540 (YY1540), had varying degrees of infestation by C. medinalis. However, it is currently unclear whether the reason for this difference is related to the difference in defense ability of the three rice varieties against the infestation of C. medinalis. To explore this issue, the current study investigated the effects of three rice varieties on the growth performance and food utilization capability of the 4th instar C. medinalis. Further, it elucidated the differences in defense responses among different rice varieties based on the differences in leaf physiological and biochemical indicators and their impact on population occurrence. The results showed that the larval survival rate was the lowest, and the development period was significantly prolonged after feeding on YY1540. This was not related to the differences in leaf wax, pigments, and nutritional components among the three rice varieties nor to the feeding preferences of the larvae. The rate of superoxide anion production, hydrogen peroxide content, and the activity of three protective enzymes were negatively correlated with larval survival rate, and they all showed the highest in YY1540 leaves. Compared to other tested varieties, although the larvae feeding on YY1540 had higher conversion efficiency of ingested food and lower relative consumption rate, their relative growth was faster, indicating stronger food utilization capability. However, they had a lower accumulation of protein. This suggests that different rice varieties had different levels of oxidative stress after infestation by C. medinalis. The defense response of YY1540 was more intense, which was not conducive to the development of the larvae population. These results will provide new insights into the interaction mechanism between different rice varieties and C. medinalis and provide a theoretical basis for cultivating rice varieties resistant to this pest.

The N-terminal α2 helix element is critical for the activity of the rice transcription factor MYC2

Jasmonates (JAs) are a class of phytohormones that play a crucial role in plant growth, development, and environmental stress responses. Central to JA signaling are the MYC2-type transcription factors, as they activate the expression of JA-responsive genes. We previously used CRISPR-Cas9-based genome editing to engineer rice OsMYC2 and yielded a mutant (myc2-5) with a single amino acid (aa) deletion (75I) outside the known functional domains of the protein. This myc2-5 mutant also showed some JA-deficient phenotypes, promoting us to investigate how 75I deletion affects JA responses. The mutation is found in the α2 helix element at the N-terminal of OsMYC2. The deletion of 75I in OsMYC2 rendered plants deficient in most of the JA responses, including root growth, leaf senescence, spikelet development, and resistance to pathogens and herbivores. Biochemical assays revealed that the 75I deletion markedly reduced OsMYC2 protein accumulation, subsequently diminishing its transcriptional activity. However, the deletion did not influence the protein's subcellular localization, DNA-binding capability, or its interactions with JAZ transcriptional repressors and the Mediator complex subunit MED25. Additionally, the screening of seven other deletions in the α2 helix further reinforces the importance of this protein element. Our results highlight the significance of the α2 helix in the N-terminus for OsMYC2's functionality, primarily through modulating its protein levels. This insight expands our knowledge of JA signaling and opens new avenues for research into the yet-to-be-explored domains of the MYC2 protein, with the potential to tailor JA responses in rice and other plant species.

Knocking down a DNA demethylase gene affects potato plant defense against a specialist insect herbivore

DNA demethylase (DML) is involved in plant development and responses to biotic and abiotic stresses; however, its role in plant-herbivore interaction remains elusive. Here, we found that herbivory by the potato tuber moth, Phthorimaea operculella, rapidly induced the genome-wide DNA methylation and accumulation of DML gene transcripts in potato plants. Herbivory induction of DML transcripts was suppressed in jasmonate-deficient plants, whereas exogenous application of methyl jasmonate (MeJA) improved DML transcripts, indicating that the induction of DML transcripts by herbivory is associated with jasmonate signaling. Moreover, P. operculella larvae grew heavier on DML gene (StDML2) knockdown plants than on wild-type plants, and the decreased biosynthesis of jasmonates in the former may be responsible for this difference, since the larvae feeding on these two genotypes supplemented with MeJA showed similar growth. In addition, P. operculella adult moths preferred to oviposit on StDML2 knockdown plants than on wild-type plants, which was associated with the reduced emission of β-caryophyllene in the former. In addition, supplementing β-caryophyllene to these two genotypes further disrupted moths' oviposit choice preference for them. Interestingly, in StDML2 knockdown plants, hypermethylation was found at the promoter regions for the key genes StAOS and StAOC in the jasmonate biosynthetic pathway, as well as for the key gene StTPS12 in β-caryophyllene production. Our findings suggest that knocking down StDML2 can affect herbivore defense via jasmonate signaling and defense compound production in potato plants.

Calcium (Ca2+ ) sensors and MYC2 are crucial players during jasmonates-mediated abiotic stress tolerance in plants

Plants evolve stress-specific responses that sense changes in their external environmental conditions and develop various mechanisms for acclimatization and survival. Calcium (Ca2+ ) is an essential stress-sensing secondary messenger in plants. Ca2+ sensors, including calcium-dependent protein kinases (CDPKs), calmodulins (CaMs), CaM-like proteins (CMLs), and calcineurin B-like proteins (CBLs), are involved in jasmonates (JAs) signalling and biosynthesis. Moreover, JAs are phospholipid-derived phytohormones that control plant response to abiotic stresses. The JAs signalling pathway affects hormone-receptor gene transcription by binding to the basic helix-loop-helix (bHLH) transcription factor. MYC2 acts as a master regulator of JAs signalling module assimilated through various genes. The Ca2+ sensor CML regulates MYC2 and is involved in a distinct mechanism mediating JAs signalling during abiotic stresses. This review highlights the pivotal role of the Ca2+ sensors in JAs biosynthesis and MYC2-mediated JAs signalling during abiotic stresses in plants.

Functional dissection of rice jasmonate receptors involved in development and defense

The phytohormones, jasmonates (JAs), mediate many plant developmental processes and their responses to important environmental stresses, such as herbivore attack. Bioactive JAs are perceived by CORONATINE INSENSITIVE (COI)-receptors, and associated JAZ proteins, to activate downstream responses. To date, the JA receptors of the important monocot crop plant, rice, remain to be explored. Here, we studied all three rice COI proteins, OsCOI1a, OsCOI1b, and OsCOI2, by ligand binding, genome editing, and phenotyping and examining some of the responsible mechanisms for the different responses. OsCOI2 binds to most individual OsJAZs in the presence of endogenous JA ligands, as OsCOI1a /1b do, albeit with greater partner selectivity. Single mutants of each OsCOI and OsCOI1a/1b double mutants were constructed by CRIPSR-Cas9-based genome editing and used to phenotype developmental and defense responses. OsCOI1b is involved in root growth and grain-size control and plays overlapping roles with OsCOI1a in spikelet development, while OsCOI2 regulates leaf senescence, male sterility, root growth, and grain size. All OsCOIs mediated resistance to the devastating rice pest, the brown planthopper. However, the defense sectors regulated by OsCOI1a/1b and OsCOI2 clearly differed. Our results revealed that all three OsCOIs are functional JA receptors that play diverse roles in regulating downstream JA responses.

Insect Herbivory on Main Stem Enhances Induced Defense of Primary Tillers in Rice (Oryza sativa L.)

Clonal plants are interconnected to form clonal plant networks with physiological integration, enabling the reassignment as well as sharing of resources among the members. The systemic induction of antiherbivore resistance via clonal integration may frequently operate in the networks. Here, we used an important food crop rice (Oryza sativa), and its destructive pest rice leaffolder (LF; Cnaphalocrocis medinalis) as a model to examine defense communication between the main stem and clonal tillers. LF infestation and MeJA pretreatment on the main stem for two days reduced the weight gain of LF larvae fed on the corresponding primary tillers by 44.5% and 29.0%, respectively. LF infestation and MeJA pretreatment on the main stem also enhanced antiherbivore defense responses in primary tillers: increased levels of a trypsin protease inhibitor, putative defensive enzymes, and jasmonic acid (JA), a key signaling compound involved in antiherbivore induced defenses; strong induction of genes encoding JA biosynthesis and perception; and rapid activation of JA pathway. However, in a JA perception OsCOI RNAi line, LF infestation on main stem showed no or minor effects on antiherbivore defense responses in primary tillers. Our work demonstrates that systemic antiherbivore defense operate in the clonal network of rice plants and JA signaling plays a crucial role in mediating defense communication between main stem and tillers in rice plants. Our findings provide a theoretical basis for the ecological control of pests by using the systemic resistance of cloned plants themselves.

Elevating herbivore-induced JA-Ile enhances potato resistance to the polyphagous beet armyworm but not to the oligophagous potato tuber moth

BACKGROUND

The oligophagous potato tuber moth (PTM), Phthorimaea operculella, and the polyphagous beet armyworm (BAW), Spodoptera exigua, are two destructive pests of potato, and infestations can lead to serious reduction in potato yield. However, potato plant responses to the two herbivories are only poorly understood. Endogenous jasmonoyl-isoleucine (JA-Ile) is a signal responsible for the induction of plant anti-herbivore defenses. Elevation of JA-Ile by blocking its catabolism is considered to be an effective and sustainable approach to enhance plant resistance to insect pests. However, it is not clear whether this approach can enhance potato resistance to PTM and BAW.

RESULTS

We demonstrated that the transcriptional changes induced by simulated PTM and BAW feeding overlap to a large extent, and that 81.5% of the PTM- and 90.5% of the BAW-responsive genes were commonly regulated. We also generated potato transgenic lines, irStCYP94B3s, in which the three JA-Ile hydroxylases were all simultaneously silenced. These lines exhibited enhanced resistance only to BAW, but not to PTM, although levels of JA-Ile and its downstream induced defensive chemicals, including caffeoylputrescine, dicaffeoylspermidine, lyciumoside II, and the nicotianosides I, II, and VII, were all present at higher levels in PTM-infested than in BAW-infested irStCYP94B3s lines.

CONCLUSION

Our results provide support for the hypothesis that StCYP94B3 genes are able to act as potential targets for the control of polyphagous insect pests in potato, and reveal that the oligophagous PTM has evolved an effective mechanism to cope with JA-Ile-induced anti-herbivore defenses. © 2022 Society of Chemical Industry.