A highly accumulated secretory protein from cotton bollworm interacts with basic helix-loop-helix transcription factors to dampen plant defense

Nitrogen-mediated volatilisation of defensive metabolites in tomato confers resistance to herbivores

Plants synthesise a vast array of volatile organic compounds (VOCs), which serve as chemical defence and communication agents in their interactions with insect herbivores. Although nitrogen (N) is a critical resource in the production of plant metabolites, its regulatory effects on defensive VOCs remain largely unknown. Here, we investigated the effect of N content in tomato (Solanum lycopersicum) on the tobacco cutworm (Spodoptera litura), a notorious agricultural pest, using biochemical and molecular experiments in combination with insect behavioural and performance analyses. We observed that on tomato leaves with different N contents, S. litura showed distinct feeding preference and growth and developmental performance. Particularly, metabolomics profiling revealed that limited N availability conferred resistance upon tomato plants to S. litura is likely associated with the biosynthesis and emission of the volatile metabolite α-humulene as a repellent. Moreover, exogenous application of α-humulene on tomato leaves elicited a significant repellent response against herbivores. Thus, our findings unravel the key factors involved in N-mediated plant defence against insect herbivores and pave the way for innovation of N management to improve the plant defence responses to facilitate pest control strategies within agroecosystems.

The proteomic landscape of fall armyworm oral secretion reveals its role in plant adaptation

BACKGROUND

The fall armyworm (FAW, Spodoptera frugiperda (J.E. Smith)) is a polyphagous agricultural pest with rapidly evolving adaptations to host plants. We found the oral secretion (OS) of FAW from different plants influences plant defense response differentially, suggesting its role in adapting to host plants. However, the protein expression profile of FAW OS respond to different plants is largely unknown.

RESULTS

Here, from the mass spectrometry assay, we identified a total of 256 proteins in the OS of FAW fed on cotton (Gossypium hirsutum L.), tobacco (Nicotiana benthamiana Domin), maize (Zea mays L.) and artificial diet. The FAW OS primarily comprise of 60 proteases, 32 esterases and 92 non-enzymatic proteins. It displays high plasticity across different diets. We found that more than half of the esterases are lipases which have been reported as insect elicitors to enhance plant defense response. The lipase accumulation in cotton-fed larvae was the highest, followed by maize-fed larvae. In the presence of lipase inhibitors, the enhanced induction on defense genes in wounded leaves by OS was attenuated. However, the putative effectors were most highly accumulated in the OS from FAW larvae fed on maize compared to those fed on other diets. We identified that one of them (VRLP4) reduces the OS-mediated induction on defense genes in wounded leaves.

CONCLUSION

Together, our investigation presents the proteomic landscape of the OS of FAW influenced by different diets and reveals diet-mediated plasticity of OS is involved in FAW adaptation to host plants. © 2024 Society of Chemical Industry.

Dephosphorylation of the MAP kinases MPK6 and MPK3 fine-tunes responses to wounding and herbivory in Arabidopsis

The Arabidopsis MAP Kinases (MAPKs) MPK6 and MPK3 and orthologs in other plants function as major stress signaling hubs. MAPKs are activated by phosphorylation and are negatively regulated by MAPK-inactivating phosphatases (MIPPs), which alter the intensity and duration of MAPK signaling via dephosphorylation. Unlike in other plant species, jasmonic acid (JA) accumulation in Arabidopsis is apparently not MPK6- and MPK3-dependent, so their role in JA-mediated defenses against herbivorous insects is unclear. Here we explore whether changes in MPK6/3 phosphorylation kinetics in Arabidopsis MIPP mutants lead to changes in hormone synthesis and resistance against herbivores. The MIPPs MKP1, DsPTP1, PP2C5, and AP2C1 have been implicated in responses to infection, drought, and osmotic stress, which all impinge on JA-mediated defenses. In loss-of-function mutants, we found that the four MIPPs alter wound-induced MPK6/3 phosphorylation kinetics and affect the accumulation of the defense hormones JA, abscisic acid, and salicylic acid, as compared to wild type plants (Col-0). Moreover, MPK6/3 misregulation in MIPP or MAPK mutant plants resulted in slight changes in the resistance to Trichoplusia ni and Spodoptera exigua larvae as compared to Col-0. Our data indicate that MPK6/3 and the four MIPPs moderately contribute to wound signaling and defense against herbivorous insects in Arabidopsis.

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.

Single-cell RNA sequencing reveals a hierarchical transcriptional regulatory network of terpenoid biosynthesis in cotton secretory glandular cells

Plants can synthesize a wide range of terpenoids in response to various environmental cues. However, the specific regulatory mechanisms governing terpenoid biosynthesis at the cellular level remain largely elusive. In this study, we employed single-cell RNA sequencing to comprehensively characterize the transcriptome profile of cotton leaves and established a hierarchical transcriptional network regulating cell-specific terpenoid production. We observed substantial expression levels of genes associated with the biosynthesis of both volatile terpenes (such as β-caryophyllene and β-myrcene) and non-volatile gossypol-type terpenoids in secretory glandular cells. Moreover, two novel transcription factors, namely GoHSFA4a and GoNAC42, are identified to function downstream of the Gossypium PIGMENT GLAND FORMATION genes. Both transcription factors could directly regulate the expression of terpenoid biosynthetic genes in secretory glandular cells in response to developmental and environmental stimuli. For convenient retrieval of the single-cell RNA sequencing data generated in this study, we developed a user-friendly web server . Our findings not only offer valuable insights into the precise regulation of terpenoid biosynthesis genes in cotton leaves but also provide potential targets for cotton breeding endeavors.

A comprehensive overview of cotton genomics, biotechnology and molecular biological studies

Cotton is an irreplaceable economic crop currently domesticated in the human world for its extremely elongated fiber cells specialized in seed epidermis, which makes it of high research and application value. To date, numerous research on cotton has navigated various aspects, from multi-genome assembly, genome editing, mechanism of fiber development, metabolite biosynthesis, and analysis to genetic breeding. Genomic and 3D genomic studies reveal the origin of cotton species and the spatiotemporal asymmetric chromatin structure in fibers. Mature multiple genome editing systems, such as CRISPR/Cas9, Cas12 (Cpf1) and cytidine base editing (CBE), have been widely used in the study of candidate genes affecting fiber development. Based on this, the cotton fiber cell development network has been preliminarily drawn. Among them, the MYB-bHLH-WDR (MBW) transcription factor complex and IAA and BR signaling pathway regulate the initiation; various plant hormones, including ethylene, mediated regulatory network and membrane protein overlap fine-regulate elongation. Multistage transcription factors targeting CesA 4, 7, and 8 specifically dominate the whole process of secondary cell wall thickening. And fluorescently labeled cytoskeletal proteins can observe real-time dynamic changes in fiber development. Furthermore, research on the synthesis of cotton secondary metabolite gossypol, resistance to diseases and insect pests, plant architecture regulation, and seed oil utilization are all conducive to finding more high-quality breeding-related genes and subsequently facilitating the cultivation of better cotton varieties. This review summarizes the paramount research achievements in cotton molecular biology over the last few decades from the above aspects, thereby enabling us to conduct a status review on the current studies of cotton and provide strong theoretical support for the future direction.

Diversification of JAZ-MYC signaling function in immune metabolism

Jasmonate (JA) re-programs metabolism to confer resistance to diverse environmental threats. Jasmonate stimulates the degradation of JASMONATE ZIM-DOMAIN (JAZ) proteins that repress the activity of MYC transcription factors. In Arabidopsis thaliana, MYC and JAZ are encoded by 4 and 13 genes, respectively. The extent to which expansion of the MYC and JAZ families has contributed to functional diversification of JA responses is not well understood. Here, we investigated the role of MYC and JAZ paralogs in controlling the production of defense compounds derived from aromatic amino acids (AAAs). Analysis of loss-of-function and dominant myc mutations identified MYC3 and MYC4 as the major regulators of JA-induced tryptophan metabolism. We developed a JAZ family-based, forward genetics approach to screen randomized jaz polymutants for allelic combinations that enhance tryptophan biosynthetic capacity. We found that mutants defective in all members (JAZ1/2/5/6) of JAZ group I over-accumulate AAA-derived defense compounds, constitutively express marker genes for the JA-ethylene branch of immunity and are more resistant to necrotrophic pathogens but not insect herbivores. In defining JAZ and MYC paralogs that regulate the production of amino-acid-derived defense compounds, our results provide insight into the specificity of JA signaling in immunity.

Advances of herbivore-secreted elicitors and effectors in plant-insect interactions

Diverse molecular processes regulate the interactions between insect herbivores and their host plants. When plants are exposed to insects, elicitors induce plant defenses, and complex physiological and biochemical processes are triggered, such as the activation of the jasmonic acid (JA) and salicylic acid (SA) pathways, Ca2+ flux, reactive oxygen species (ROS) burst, mitogen-activated protein kinase (MAPK) activation, and other responses. For better adaptation, insects secrete a large number of effectors to interfere with plant defenses on multiple levels. In plants, resistance (R) proteins have evolved to recognize effectors and trigger stronger defense responses. However, only a few effectors recognized by R proteins have been identified until now. Multi-omics approaches for high-throughput elicitor/effector identification and functional characterization have been developed. In this review, we mainly highlight the recent advances in the identification of the elicitors and effectors secreted by insects and their target proteins in plants and discuss their underlying molecular mechanisms, which will provide new inspiration for controlling these insect pests.