The lipoxygenase gene OsRCI-1 is involved in the biosynthesis of herbivore-induced JAs and regulates plant defense and growth in rice

Glutamate induction of whole potatoes alleviated the browning of fresh cuts: Jasmonate signalling may play a key role

Enzymatic browning is one of the most troublesome issues for fresh-cut fruits and vegetables, as it not only reduces product quality and shelf life but also causes great waste and economic loss. Although many antibrowning technologies have been explored, few noncontact methods have been reported. In particular, the effect of using glutamate (Glu) is unknown. This study revealed that Glu treatment of whole tubers significantly reduced browning in fresh-cut potatoes. This whole-tuber Glu induction under optimal conditions (1 % Glu for 12 h) produced a brighter colour and better sensory quality than soaking slices in solutions of Glu or ascorbic acid. Notably, Glu induction led to increased jasmonic acid (JA) and jasmonate-isoleucine (JA-Ile) accumulation. The activities of 12-oxophytodienoic acid reductase 3 (OPR3), jasmonate-resistant 1 (JAR1), and coronatine-insensitive 1 (COI1) in the jasmonate synthesis pathway and the expression of their corresponding genes also increased. Additionally, phenylpropane metabolism was upregulated, as evidenced by increased levels of phenylalanine ammonia-lyase (PAL), 4-coumaric acid coenzyme a ligase (4CL), phenolic compounds and flavonoids. Moreover, the reactive oxygen species (ROS)-redox balance improved, the contents of hydrogen peroxide and malondialdehyde (MDA) decreased, and the catalase (CAT) activity and 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) scavenging capacity increased. Finally, Glu induction increased microbiological safety, resulting in a lower total bacterial count. Thus, Glu induction may modulate jasmonic acid synthesis and signalling, regulate phenylpropane metabolism and the reactive oxygen species (ROS)-redox balance, and ultimately slow browning and improve storage quality in fresh-cut potatoes. This is the first report of a noncontact browning control technique involving Glu, which provides new ideas for the fresh-cut industry.

Both Jasmonic Acid- and Abscisic Acid-Mediated Signalling Pathways Regulate the Ovicidal Defence of Plants Against Phloem-Feeding Insects

Plants perceive signals associated with herbivore eggs and in response initiate ovicidal defence. However, which phytohormone pathways regulate this defence and which defensive compounds dominate it remains largely unknown. Here, we found that the hatching rate of eggs of white-backed planthopper (WBPH) Sogatella furcifera was significantly lower on a japonica rice variety P81 than an indica rice variety NB44. When infested by WBPH, P81 plants showed higher jasmonic acid (JA) and abscisic acid (ABA) responses than did NB44 plants; moreover, P81 plants produced the ovicidal compound benzyl benzoate and exhibited higher levels of some flavonoids, phenolamides, and volatiles than were found in NB44 plants. Impairing the ABA-signalling pathway, especially the JA-signalling pathway in P81 plants enhanced the survival of WBPH eggs. Decreasing levels of some flavonoids and phenolamides in P81 plants promoted WBPH egg survival. In vitro bioassays revealed that both naringenin and sakuranetin promote the ovicidal effect of benzyl benzoate on WBPH. The results demonstrate that JA- and ABA-signalling pathways jointly regulate the rice ovicidal defence against WBPH, and that benzyl benzoate, as well as some other compounds, such as naringenin and sakuranetin, contribute to the mortality of WBPH eggs.

Exploitation of volatile organic compounds for rice field insect-pest management: current status and future prospects

Insect pests are major biotic factors that cause significant damage to rice crops, posing a major challenge to global rice production. Synthetic pesticides are the most effective and reliable technique for pest management. However, their high cost, non-biodegradability, and adverse effects on human and environmental health have driven the search for more sustainable, eco-friendly, and economically viable alternatives. Recently, Volatile Organic Compounds (VOCs), both plant-derived or synthetically made, have emerged as a promising tool for insect pest management in diverse agricultural practices. Rice plants continuously release VOCs that facilitate tritrophic interactions among the plants, their herbivores, and the natural enemies of these herbivores, highlighting their ecological importance. VOCs are being explored as semiochemicals in pest management strategies in various crops, including rice. Although applications of VOCs remain in the laboratory stage, they hold great promise for future field implementation. This review highlights the role of rice VOCs in herbivore-natural enemy interactions and explores the factors regulating their release. It provides a comprehensive analysis of recent advancements, ongoing challenges, and prospects in using VOCs for rice pest management. Additionally, the review emphasizes the integration of VOCs with precision agriculture and genetic engineering approaches along with advanced monitoring technologies, to develop sustainable and effective pest management practices in rice agroecosystems.

The MYC2-JAMYB transcriptional cascade regulates rice resistance to brown planthoppers

Plant defense against herbivores is primarily regulated by the phytohormone jasmonate (JA). At the core, JA signaling is the MYC2 transcription factor (TF) that regulates the expression of an extensive array of defense-related genes. However, the regulatory mechanisms underlying MYC2-mediated herbivore resistance in rice are not fully understood. We employed brown planthopper (BPH) bioassays, transcriptional activation assays, transcriptome profiling, targeted metabolomics and cleavage under targets and tagmentation-sequencing analysis to investigate the biological function and regulatory mechanism of the JAMYB TF. JAMYB is induced by BPH infestation and is transcriptionally regulated by MYC2. Mutations of JAMYB rendered rice plants susceptible to BPH attacks under laboratory and field conditions, indicating that JAMYB positively contributes to BPH resistance. BPH-elicited biosynthesis of phenolamides and volatile compounds was reduced in jamyb mutants compared with wild-type plants. These specialized metabolites, regulated by JAMYB, function as direct and indirect defenses to deter BPH damage or attract parasitoid wasps of BPH eggs. Furthermore, we found that JAMYB directly binds to AC motifs of key phenylpropanoid pathway genes and activates their expression, likely altering the metabolic flux for phenolamide biosynthesis. This study reveals the role of the MYC2-JAMYB module in JA-mediated rice resistance to BPH.

Red Light Induces Powdery Mildew Resistance by Activating the Expression of CmLOX10 in Oriental Melon

Powdery mildew (PM) is a serious fungal disease in plant cultivation, which is detrimental to the yield and quality of oriental melons. Lipoxygenases (LOXs) are widely involved in pathogen stress response. Our previous studies have indicated that red light (RL) can induce defense to PM in oriental melon seedlings. However, it remains unclear whether LOXs are involved in this process. In this study, we found that LOX activity is essential for RL-induced PM resistance, with CmLOX10 is identified as a key member. We conducted a yeast one-hybrid (Y1H) screening of oriental melon cDNA libraries using the CmLOX10 promoter, which led to the identification of CmWRKY41 and CmABL5. Both of these proteins can regulate the expression of CmLOX10, thereby participating in the RL-induced PM resistance process. Furthermore, phytochrome B (phyB) interacts with CmABL5 at the protein level, enhancing its transcriptional activation of CmLOX10. Silencing CmphyB undermines the induction of RL resistance to PM. Our study elucidates the activation mechanism of CmLOX10 involved in PM resistance following RL induction, thereby enriching the network of interaction between light and pathogenic fungi.

Jasmonic Acid (JA) Signaling Pathway in Rice Defense Against Chilo suppressalis Infestation

Jasmonic acid (JA) signaling plays a crucial role in rice defense against the striped stem borer, Chilo suppressalis, a notorious pest causing significant yield losses. This review explores the current understanding of JA-mediated defense mechanisms in rice, focusing on the molecular basis, regulatory elements, and practical implications for pest management. JA biosynthesis and signaling pathways are induced upon C. suppressalis infestation, leading to the activation of various defense responses. These include upregulation of JA-responsive genes involved in the production of proteinase inhibitors, volatile organic compounds, and other defensive compounds. The review also discusses the crosstalk between JA and other hormonal pathways, such as salicylic acid and ethylene, in fine-tuning defense responses. Structural modifications in rice plants, such as cell wall reinforcement and accumulation of secondary metabolites, have been highlighted as key components of JA-mediated defense against C. suppressalis. Furthermore, the practical applications of this knowledge in breeding insect-resistant rice varieties and developing sustainable pest management strategies were explored. Future research directions are proposed to further elucidate the complexities of JA signaling in rice-insect interactions and harness this knowledge to enhance crop protection.

Ethylene-Mediated Production and Emission of Limonene Influence Brown Planthopper Preference for Rice Plants

Volatile organic compounds (VOCs) play a key role in plant communication with other organisms in the natural environment. However, the regulatory role of the phytohormone ethylene in volatile production in plants remains unclear. In this study, we demonstrated that the application of an ethylene precursor and amplification of ethylene signaling make rice plants more attractive to brown planthopper (BPH) females for feeding and oviposition. A combination of transcriptome and VOCs analyses indicated that overexpression of OsEIL1, a master transcription factor in the ethylene pathway, influences the transcript levels of several terpene synthase genes as well as the production of volatile terpenes. Further investigation revealed that the expression of the limonene synthase gene, OsTPS19, was down-regulated in OsEIL1-overexpressing rice plants, leading to a decrease in limonene production and release. Genetic analysis confirmed the essential role of limonene in the OsEIL1-mediated attractiveness of rice plants to BPH. Our findings provide new perspectives for understanding the role of ethylene signaling in volatile-mediated plant-insect interactions.

Biological Roles of Lipids in Rice

Lipids are organic nonpolar molecules with essential biological and economic importance. While the genetic pathways and regulatory networks of lipid biosynthesis and metabolism have been extensively studied and thoroughly reviewed in oil crops such as soybeans, less attention has been paid to the biological roles of lipids in rice, a staple food for the global population and a model species for plant molecular biology research, leaving a considerable knowledge gap in the biological roles of lipids. In this review, we endeavor to furnish a current overview of the advancements in understanding the genetic foundations and physiological functions of lipids, including triacylglycerol, fatty acids, and very-long-chain fatty acids. We aim to summarize the key genes in lipid biosynthesis, metabolism, and transcriptional regulation underpinning rice's developmental and growth processes, biotic stress responses, abiotic stress responses, fertility, seed longevity, and recent efforts in rice oil genetic improvement.

Exploring selection signatures in the divergence and evolution of lipid droplet (LD) associated genes in major oilseed crops

BACKGROUND

Oil bodies or lipid droplets (LDs) in the cytosol are the subcellular storage compartments of seeds and the sites of lipid metabolism providing energy to the germinating seeds. Major LD-associated proteins are lipoxygenases, phospholipaseD, oleosins, TAG-lipases, steroleosins, caleosins and SEIPINs; involved in facilitating germination and enhancing peroxidation resulting in off-flavours. However, how natural selection is balancing contradictory processes in lipid-rich seeds remains evasive. The present study was aimed at the prediction of selection signatures among orthologous clades in major oilseeds and the correlation of selection effect with gene expression.

RESULTS

The LD-associated genes from the major oil-bearing crops were analyzed to predict natural selection signatures in phylogenetically close-knit ortholog clusters to understand adaptive evolution. Positive selection was the major force driving the evolution and diversification of orthologs in a lineage-specific manner. Significant positive selection effects were found in 94 genes particularly in oleosin and TAG-lipases, purifying with excess of non-synonymous substitution in 44 genes while 35 genes were neutral to selection effects. No significant selection impact was noticed in Brassicaceae as against LOX genes of oil palm. A heavy load of deleterious mutations affecting selection signatures was detected in T-lineage oleosins and LOX genes of Arachis hypogaea. The T-lineage oleosin genes were involved in mainly anther, tapetum and anther wall morphogenesis. In Ricinus communis and Sesamum indicum > 85% of PLD genes were under selection whereas selection pressures were low in Brassica juncea and Helianthus annuus. Steroleosin, caleosin and SEIPINs with large roles in lipid droplet organization expressed mostly in seeds and were under considerable positive selection pressures. Expression divergence was evident among paralogs and homeologs with one gene attaining functional superiority compared to the other. The LOX gene Glyma.13g347500 associated with off-flavor was not expressed during germination, rather its paralog Glyma.13g347600 showed expression in Glycine max. PLD-α genes were expressed on all the tissues except the seed,δ genes in seed and meristem while β and γ genes expressed in the leaf.

CONCLUSIONS

The genes involved in seed germination and lipid metabolism were under strong positive selection, although species differences were discernable. The present study identifies suitable candidate genes enhancing seed oil content and germination wherein directional selection can become more fruitful.

OsRCI-1-Mediated GLVs Enhance Rice Resistance to Brown Planthoppers

Green leaf volatiles (GLVs) play pivotal roles in plant anti-herbivore defense. This study investigated whether the rice 13-lipoxygense gene OsRCI-1 is involved in GLV production and plant defense in rice. The overexpression of OsRCI-1 (oeRCI lines) in rice resulted in increased wound-induced levels of two prominent GLVs, cis-3-hexen-1-ol and cis-3-hexenal. In a previous study, we found that the overexpression of OsRCI-1 reduced the colonization by the rice brown planthopper (BPH, Nilaparvata lugens) but increased the attractiveness to the egg parasitoid Anagrus nilaparvatae compared to wild-type (WT) plants. This study found that when cis-3-hexen-1-ol, but not cis-3-hexenal, was added to WT plants, it could change the BPH's colonization preference, i.e., more BPHs preferred to colonize the oeRCI lines. The exogenous application of cis-3-hexen-1-ol or cis-3-hexenal to BPH-infested WT plants could weaken or overturn the preference of A. nilaparvatae for oeRCI lines. However, field experiments revealed that only cis-3-hexenal was attractive to the parasitoid and increased the parasitism rates of BPH eggs. These results indicate that OsRCI-1 is involved in rice GLV production and therefore modulates both direct and indirect defense in rice.

OsmiR319-OsPCF5 modulate resistance to brown planthopper in rice through association with MYB proteins

BACKGROUND

The brown planthopper (BPH) is a kind of piercing-sucking insect specific to rice, with the damage tops the list of pathogens and insects in recent years. microRNAs (miRNAs) are pivotal regulators of plant-environment interactions, while the mechanism underlying their function against insects is largely unknown.

RESULTS

Here, we confirmed that OsmiR319, an ancient and conserved miRNA, negatively regulated resistance to BPHs, with overexpression of OsmiR319 susceptible to BPH, while suppression of OsmiR319 resistant to BPH in comparison with wild type. Meanwhile, we identified several targets of OsmiR319 that may mediate BPH resistance. Among them, OsPCF5 was the most obviously induced by BPH feeding, and over expression of OsPCF5 was resistance to BPH. In addition, various biochemical assays verified that OsPCF5 interacted with several MYB proteins, such as OsMYB22, OsMYB30, and OsMYB30C.Genetically, we revealed that both OsMYB22 and OsMYB30C positively regulated BPH resistance. Genetic interaction analyses confirmed that OsMYB22 and OsMYB30C both function in the same genetic pathway with OsmiR319b to mediate BPH resistance.

CONCLUSIONS

Altogether, we revealed that OsPCF5 regulates BPH resistance via association with several MYB proteins downstream of OsmiR319, these MYB proteins might function as regulators of BPH resistance through regulating the phenylpropane synthesis.

The intricate role of lipids in orchestrating plant defense responses

Plants are exposed to a variety of pests and pathogens that reduce crop productivity. Plants respond to such attacks by activating a sophisticated signaling cascade that initiates with the recognition of pests/pathogens and may culminate into a resistance response. Lipids, being the structural components of cellular membranes, function as mediators of these signaling cascades and thus are instrumental in the regulation of plant defense responses. Accumulating evidence indicates that various lipids such as oxylipins, phospholipids, glycolipids, glycerolipids, sterols, and sphingolipids, among others, are involved in mediating cell signaling during plant-pathogen interaction with each lipid exhibiting a specific biological relevance, follows a distinct biosynthetic mechanism, and contributes to specific signaling cascade(s). Omics studies have further confirmed the involvement of lipid biosynthetic enzymes including the family of phospholipases in the production of defense signaling molecules subsequent to pathogen attack. Lipids participate in stress signaling by (1) mediating the signal transduction, (2) acting as precursors for bioactive molecules, (3) regulating ROS formation, and (4) interacting with various phytohormones to orchestrate the defense response in plants. In this review, we present the biosynthetic pathways of different lipids, their specific functions, and their intricate roles upstream and downstream of phytohormones under pathogen attack to get a deeper insight into the molecular mechanism of lipids-mediated regulation of defense responses in plants.

Integration of transcriptome and metabolome analyses reveals the role of OsSPL10 in rice defense against brown planthopper

KEY MESSAGE

OsSPL10 is a negative regulator of rice defense against BPH, knockout of OsSPL10 enhances BPH resistance through upregulation of defense-related genes and accumulation of secondary metabolites. Rice (Oryza sativa L.), one of the most important staple foods worldwide, is frequently attacked by various herbivores, including brown planthopper (BPH, Nilaparvata lugens). BPH is a typical monophagous, phloem-sucking herbivore that has been a substantial threat to rice production and global food security. Understanding the regulatory mechanism of defense responses to BPH is essential for improving BPH resistance in rice. In this study, a SQUAMOSA PROMOTER-BINDING PROTEIN-LIKE 10 (OsSPL10) transcription factor was found to play a negative role in the defenses of rice against BPH. To gain insights into the molecular and biochemical mechanisms of OsSPL10, we performed combined analyses of transcriptome and metabolome, and revealed that knockout of OsSPL10 gene improved rice resistance against BPH by enhancing the direct and indirect defenses. Genes involved in plant hormone signal transduction, MAPK signaling pathway, phenylpropanoid biosynthesis, and plant-pathogen interaction pathway were significantly upregulated in spl10 mutant. Moreover, spl10 mutant exhibited increased accumulation of defense-related secondary metabolites in the phenylpropanoid and terpenoid pathways. Our findings reveal a novel role for OsSPL10 gene in regulating the rice defense responses, which can be used as a potential target for genetic improvement of BPH resistance in rice.

Silencing a dehydration-responsive element-binding gene enhances the resistance of plants to a phloem-feeding herbivore

Herbivore-induced plant defence responses share common components with plant responses to abiotic stresses. However, whether abiotic stress-responsive factors influence the resistance of plants to herbivores by regulating these components remains largely unknown. Here, we cloned a dehydration-responsive element-binding gene in rice, OsDREB1A, and investigated its role in the resistance of rice to the phloem-feeding herbivore, brown planthopper (BPH, Nilaparvata lugens), under normal and low temperatures. We found that OsDREB1A localized to the nucleus, and its transcripts in rice were up-regulated in response to BPH infestation, low temperatures and treatment with methyl jasmonate or salicylic acid. Silencing OsDREB1A changed transcript levels of two defence-related WRKY and two PLD genes, enhanced levels of jasmonic acid (JA), JA-isoleucine and abscisic acid, and decreased the ethylene level in rice; these changes subsequently enhanced the resistance of plants to BPH, especially at 17°C, by decreasing the hatching rate and delaying the development of BPH eggs. Moreover, silencing OsDREB1A increased the growth of rice plants. These findings suggest that OsDREB1A, which positively regulates the resistance of rice to abiotic stresses, negatively regulates the resistance of rice to BPH.

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.

A comprehensive dynamic immune acetylproteomics profiling induced by Puccinia polysora in maize

Lysine-ε-acetylation (Kac) is a reversible post-translational modification that plays important roles during plant-pathogen interactions. Some pathogens can deliver secreted effectors encoding acetyltransferases or deacetylases into host cell to directly modify acetylation of host proteins. However, the function of these acetylated host proteins in plant-pathogen defense remains to be determined. Employing high-resolution tandem mass spectrometry, we analyzed protein abundance and lysine acetylation changes in maize infected with Puccinia polysora (P. polysora) at 0 h, 12 h, 24 h, 48 h and 72 h. A total of 7412 Kac sites from 4697 proteins were identified, and 1732 Kac sites from 1006 proteins were quantified. Analyzed the features of lysine acetylation, we found that Kac is ubiquitous in cellular compartments and preferentially targets lysine residues in the -F/W/Y-X-X-K (ac)-N/S/T/P/Y/G- motif of the protein, this Kac motif contained proteins enriched in basic metabolism and defense-associated pathways during fungal infection. Further analysis of acetylproteomics data indicated that maize regulates cellular processes in response to P. polysora infection by altering Kac levels of histones and non-histones. In addition, acetylation of pathogen defense-related proteins presented converse patterns in signaling transduction, defense response, cell wall fortification, ROS scavenging, redox reaction and proteostasis. Our results provide informative resources for studying protein acetylation in plant-pathogen interactions, not only greatly extending the understanding on the roles of acetylation in vivo, but also providing a comprehensive dynamic pattern of Kac modifications in the process of plant immune response.

Ectopic Expression of AeNAC83, a NAC Transcription Factor from Abelmoschus esculentus, Inhibits Growth and Confers Tolerance to Salt Stress in Arabidopsis

NAC transcription factors play crucial roles in plant growth, development and stress responses. Previously, we preliminarily identified that the transcription factor AeNAC83 gene was significantly up-regulated under salt stress in okra (Abelmoschus esculentus). Herein, we cloned the nuclear-localized AeNAC83 from okra and identified its possible role in salt stress response and plant growth. The down-regulation of AeNAC83 caused by virus-induced gene silencing enhanced plant sensitivity to salt stress and increased the biomass accumulation of okra seedlings. Meanwhile, AeNAC83-overexpression Arabidopsis lines improved salt tolerance and exhibited many altered phenotypes, including small rosette, short primary roots, and promoted crown roots and root hairs. RNA-seq showed numerous genes at the transcriptional level that changed significantly in the AeNAC83-overexpression transgenic and the wild Arabidopsis with or without NaCl treatment, respectively. The expression of most phenylpropanoid and flavonoid biosynthesis-related genes was largely induced by salt stress. While genes encoding key proteins involved in photosynthesis were almost declined dramatically in AeNAC83-overexpression transgenic plants, and NaCl treatment further resulted in the down-regulation of these genes. Furthermore, DEGs encoding various plant hormone signal pathways were also identified. These results indicate that AeNAC83 is involved in resistance to salt stress and plant growth.