OsMKK3, a Stress-Responsive Protein Kinase, Positively Regulates Rice Resistance to Nilaparvata lugens via Phytohormone Dynamics

Traditional Chinese medicine Pien-Tze-Huang ameliorates LPS-induced sepsis through bile acid-mediated activation of TGR5-STAT3-A20 signalling

Pien Tze Huang (PZH), a class I nationally protected traditional Chinese medicine (TCM), has been used to treat liver diseases such as hepatitis; however, the effect of PZH on the progression of sepsis is unknown. Here, we reported that PZH attenuated lipopolysaccharide (LPS)-induced sepsis in mice and reduced LPS-induced production of proinflammatory cytokines in macrophages by inhibiting the activation of mitogen-activated protein kinase (MAPK) and nuclear factor-kappa B (NF-κB) signalling. Mechanistically, PZH stimulated signal transducer and activator of transcription 3 (STAT3) phosphorylation to induce the expression of A20, which could inhibit the activation of NF-κB and MAPK signalling. Knockdown of the bile acid (BA) receptor G protein-coupled bile acid receptor 1 (TGR5) in macrophages abolished the effects of PZH on STAT3 phosphorylation and A20 induction, as well as the LPS-induced inflammatory response, suggesting that BAs in PZH may mediate its anti-inflammatory effects by activating TGR5. Consistently, deprivation of BAs in PZH by cholestyramine resin reduced the effects of PZH on the expression of phosphorylated-STAT3 and A20, the activation of NF-κB and MAPK signalling, and the production of proinflammatory cytokines, whereas the addition of BAs to cholestyramine resin-treated PZH partially restored the inhibitory effects on the production of proinflammatory cytokines. Overall, our study identifies BAs as the effective components in PZH that activate TGR5-STAT3-A20 signalling to ameliorate LPS-induced sepsis.

MKK3 Cascade Regulates Seed Dormancy Through a Negative Feedback Loop Modulating ABA Signal in Rice

BACKGROUND

With the increasing frequency of climatic anomalies, high temperatures and long-term rain often occur during the rice-harvesting period, especially for early rice crops in tropical and subtropical regions. Seed dormancy directly affects the resistance to pre-harvest sprouting (PHS). Therefore, in order to increase rice production, it is critical to enhance seed dormancy and avoid yield losses to PHS. The elucidation and utilization of the seed dormancy regulation mechanism is of great significance to rice production. Preliminary results indicated that the OsMKKK62-OsMKK3-OsMPK7/14 module might regulate ABA sensitivity and then control seed dormancy. The detailed mechanism is still unclear.

RESULTS

The overexpression of OsMKK3 resulted in serious PHS. The expression levels of OsMKK3 and OsMPK7 were upregulated by ABA and GA at germination stage. OsMKK3 and OsMPK7 are both located in the nucleus and cytoplasm. The dormancy level of double knockout mutant mkk3/mft2 was lower than that of mkk3, indicating that OsMFT2 functions in the downstream of MKK3 cascade in regulating rice seeds germination. Biochemical results showed that OsMPK7 interacted with multiple core ABA signaling components according to yeast two-hybrid screening and luciferase complementation experiments, suggesting that MKK3 cascade regulates ABA signaling by modulating the core ABA signaling components. Moreover, the ABA response and ABA responsive genes of mpk7/14 were significantly higher than those of wild-type ZH11 when subjected to ABA treatment.

CONCLUSION

MKK3 cascade mediates the negative feedback loop of ABA signal through the interaction between OsMPK7 and core ABA signaling components in rice.

Transcriptomic and metabolomic analyses reveals keys genes and metabolic pathways in tea (Camellia sinensis) against six-spotted spider mite (Eotetranychus Sexmaculatus)

BACKGROUND

Six-spotted spider mite (Eotetranychus sexmaculatus) is one of the most damaging pests of tea (Camellia sinensis). E. sexmaculatus causes great economic loss and affects tea quality adversely. In response to pests, such as spider mites, tea plants have evolved resistance mechanisms, such as expression of defense-related genes and defense-related metabolites.

RESULTS

To evaluate the biochemical and molecular mechanisms of resistance in C. sinensis against spider mites, "Tianfu-5" (resistant to E. sexmaculatus) and "Fuding Dabai" (susceptible to E. sexmaculatus) were inoculated with spider mites. Transcriptomics and metabolomics based on RNA-Seq and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) technology were used to analyze changes in gene expression and metabolite content, respectively. RNA-Seq data analysis revealed that 246 to 3,986 differentially expressed genes (DEGs) were identified in multiple compared groups, and these DEGs were significantly enriched in various pathways, such as phenylpropanoid and flavonoid biosynthesis, plant-pathogen interactions, MAPK signaling, and plant hormone signaling. Additionally, the metabolome data detected 2,220 metabolites, with 194 to 260 differentially abundant metabolites (DAMs) identified in multiple compared groups, including phenylalanine, lignin, salicylic acid, and jasmonic acid. The combined analysis of RNA-Seq and metabolomic data indicated that phenylpropanoid and flavonoid biosynthesis, MAPK signaling, and Ca2+-mediated PR-1 signaling pathways may contribute to spider mite resistance.

CONCLUSIONS

Our findings provide insights for identifying insect-induced genes and metabolites and form a basis for studies on mechanisms of host defense against spider mites in C. sinensis. The candidate genes and metabolites identified will be a valuable resource for tea breeding in response to biotic stress.

Recent Advances in the Genetic and Biochemical Mechanisms of Rice Resistance to Brown Planthoppers (Nilaparvata lugens Stål)

Rice (Oryza sativa L.) is the staple food of more than half of Earth's population. Brown planthopper (Nilaparvata lugens Stål, BPH) is a host-specific pest of rice responsible for inducing major losses in rice production. Utilizing host resistance to control N. lugens is considered to be the most cost-effective method. Therefore, the exploration of resistance genes and resistance mechanisms has become the focus of breeders' attention. During the long-term co-evolution process, rice has evolved multiple mechanisms to defend against BPH infection, and BPHs have evolved various mechanisms to overcome the defenses of rice plants. More than 49 BPH-resistance genes/QTLs have been reported to date, and the responses of rice to BPH feeding activity involve various processes, including MAPK activation, plant hormone production, Ca2+ flux, etc. Several secretory proteins of BPHs have been identified and are involved in activating or suppressing a series of defense responses in rice. Here, we review some recent advances in our understanding of rice-BPH interactions. We also discuss research progress in controlling methods of brown planthoppers, including cultural management, trap cropping, and biological control. These studies contribute to the establishment of green integrated management systems for brown planthoppers.

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.

Single-Cell RNA sequencing of leaf sheath cells reveals the mechanism of rice resistance to brown planthopper (Nilaparvata lugens)

The brown planthopper (BPH) (Nilaparvata lugens) sucks rice sap causing leaves to turn yellow and wither, often leading to reduced or zero yields. Rice co-evolved to resist damage by BPH. However, the molecular mechanisms, including the cells and tissues, involved in the resistance are still rarely reported. Single-cell sequencing technology allows us to analyze different cell types involved in BPH resistance. Here, using single-cell sequencing technology, we compared the response offered by the leaf sheaths of the susceptible (TN1) and resistant (YHY15) rice varieties to BPH (48 hours after infestation). We found that the 14,699 and 16,237 cells (identified via transcriptomics) in TN1 and YHY15 could be annotated using cell-specific marker genes into nine cell-type clusters. The two rice varieties showed significant differences in cell types (such as mestome sheath cells, guard cells, mesophyll cells, xylem cells, bulliform cells, and phloem cells) in the rice resistance mechanism to BPH. Further analysis revealed that although mesophyll, xylem, and phloem cells are involved in the BPH resistance response, the molecular mechanism used by each cell type is different. Mesophyll cell may regulate the expression of genes related to vanillin, capsaicin, and ROS production, phloem cell may regulate the cell wall extension related genes, and xylem cell may be involved in BPH resistance response by controlling the expression of chitin and pectin related genes. Thus, rice resistance to BPH is a complicated process involving multiple insect resistance factors. The results presented here will significantly promote the investigation of the molecular mechanisms underlying the resistance of rice to insects and accelerate the breeding of insect-resistant rice varieties.

Infestation by the Piercing-Sucking Herbivore Nilaparvata lugens Systemically Triggers JA- and SA-Dependent Defense Responses in Rice

It has been well documented that an infestation of the piercing-sucking herbivore, brown planthopper (BPH), Nilaparvata lugens, activates strong local defenses in rice. However, whether a BPH infestation elicits systemic responses in rice remains largely unknown. In this study, we investigated BPH-induced systemic defenses by detecting the change in expression levels of 12 JA- and/or SA-signaling-responsive marker genes in different rice tissues upon a BPH attack. We found that an infestation of gravid BPH females on rice leaf sheaths significantly increased the local transcript level of all 12 marker genes tested except OsVSP, whose expression was induced only weakly at a later stage of the BPH infestation. Moreover, an infestation of gravid BPH females also systemically up-regulated the transcription levels of three JA-signaling-responsive genes (OsJAZ8, OsJAMyb, and OsPR3), one SA-signaling-responsive gene (OsWRKY62), and two JA- and SA- signaling-responsive genes (OsPR1a and OsPR10a). Our results demonstrate that an infestation of gravid BPH females systemically activates JA- and SA-dependent defenses in rice, which may in turn influence the composition and structure of the community in the rice ecosystem.

Plant-soil-microbe interactions in maintaining ecosystem stability and coordinated turnover under changing environmental conditions

Ecosystem functions directly depend upon biophysical as well as biogeochemical reactions occurring at the soil-microbe-plant interface. Environment is considered as a major driver of any ecosystem and for the distributions of living organisms. Any changes in climate may potentially alter the composition of communities i.e., plants, soil microbes and the interactions between them. Since the impacts of global climate change are not short-term, it is indispensable to appraise its effects on different life forms including soil-microbe-plant interactions. This article highlights the crucial role that microbial communities play in interacting with plants under environmental disturbances, especially thermal and water stress. We reviewed that in response to the environmental changes, actions and reactions of plants and microbes vary markedly within an ecosystem. Changes in environment and climate like warming, CO₂ elevation, and moisture deficiency impact plant and microbial performance, their diversity and ultimately community structure. Plant and soil feedbacks also affect interacting species and modify community composition. The interactive relationship between plants and soil microbes is critically important for structuring terrestrial ecosystems. The anticipated climate change is aggravating the living conditions for soil microbes and plants. The environmental insecurity and complications are not short-term and limited to any particular type of organism. We have appraised effects of climate change on the soil inhabiting microbes and plants in a broader prospect. This article highlights the unique qualities of tripartite interaction between plant-soil-microbe under climate change.

Engineering plant immune circuit: walking to the bright future with a novel toolbox

Plant pathogens destroy crops and cause severe yield losses, leading to an insufficient food supply to sustain the human population. Apart from relying on natural plant immune systems to combat biological agents or waiting for the appropriate evolutionary steps to occur over time, researchers are currently seeking new breakthrough methods to boost disease resistance in plants through genetic engineering. Here, we summarize the past two decades of research in disease resistance engineering against an assortment of pathogens through modifying the plant immune components (internal and external) with several biotechnological techniques. We also discuss potential strategies and provide perspectives on engineering plant immune systems for enhanced pathogen resistance and plant fitness.

Opposite roles of MAPKKK17 and MAPKKK21 against Tetranychus urticae in Arabidopsis

After recognizing a biotic stress, plants activate signalling pathways to fight against the attack. Typically, these signalling pathways involve the activation of phosphorylation cascades mediated by Mitogen-Activated Protein Kinases (MAPKs). In the Arabidopsis thaliana-Tetranychus urticae plant-herbivore model, several Arabidopsis MAP kinases are induced by the mite attack. In this study, we demonstrate the participation of the MEKK-like kinases MAPKKK17 and MAPKKK21. Leaf damage caused by the mite was assessed using T-DNA insertion lines. Differential levels of damage were found when the expression of MAPKKK17 was increased or reduced. In contrast, reduced expression of MAPKKK21 resulted in less damage caused by the mite. Whereas the expression of several genes associated with hormonal responses did not suffer significant variations in the T-DNA insertion lines, the expression of one of these kinases depends on the expression of the other one. In addition, MAPKKK17 and MAPKKK21 are coexpressed with different sets of genes and encode proteins with low similarity in the C-terminal region. Overall, our results demonstrate that MAPKKK17 and MAPKKK21 have opposite roles. MAPKKK17 and MAPKKK21 act as positive and negative regulators, respectively, on the plant response. The induction of MAPKKK17 and MAPKKK21 after mite infestation would be integrated into the bulk of signalling pathways activated to balance the response of the plant to a biotic stress.

Calcium Signaling in Plant-Insect Interactions

In plant-insect interactions, calcium (Ca²⁺) variations are among the earliest events associated with the plant perception of biotic stress. Upon herbivory, Ca²⁺ waves travel long distances to transmit and convert the local signal to a systemic defense program. Reactive oxygen species (ROS), Ca²⁺ and electrical signaling are interlinked to form a network supporting rapid signal transmission, whereas the Ca²⁺ message is decoded and relayed by Ca²⁺-binding proteins (including calmodulin, Ca²⁺-dependent protein kinases, annexins and calcineurin B-like proteins). Monitoring the generation of Ca²⁺ signals at the whole plant or cell level and their long-distance propagation during biotic interactions requires innovative imaging techniques based on sensitive sensors and using genetically encoded indicators. This review summarizes the recent advances in Ca²⁺ signaling upon herbivory and reviews the most recent Ca²⁺ imaging techniques and methods.

Plant Kinases in the Perception and Signaling Networks Associated With Arthropod Herbivory

The success in the response of plants to environmental stressors depends on the regulatory networks that connect plant perception and plant response. In these networks, phosphorylation is a key mechanism to activate or deactivate the proteins involved. Protein kinases are responsible for phosphorylations and play a very relevant role in transmitting the signals. Here, we review the present knowledge on the contribution of protein kinases to herbivore-triggered responses in plants, with a focus on the information related to the regulated kinases accompanying herbivory in Arabidopsis. A meta-analysis of transcriptomic responses revealed the importance of several kinase groups directly involved in the perception of the attacker or typically associated with the transmission of stress-related signals. To highlight the importance of these protein kinase families in the response to arthropod herbivores, a compilation of previous knowledge on their members is offered. When available, this information is compared with previous findings on their role against pathogens. Besides, knowledge of their homologous counterparts in other plant-herbivore interactions is provided. Altogether, these observations resemble the complexity of the kinase-related mechanisms involved in the plant response. Understanding how kinase-based pathways coordinate in response to a specific threat remains a major challenge for future research.

Bio-Efficacy of Chrysoeriol7, a Natural Chemical and Repellent, against Brown Planthopper in Rice

Brown planthopper (BPH, Nilaparvata lugens Stal.) is the most damaging rice pest affecting stable rice yields worldwide. Currently, methods for controlling BPH include breeding a BPH-resistant cultivar and using synthetic pesticides. Nevertheless, the continuous cultivation of resistant cultivars allows for the emergence of various resistant races, and the use of synthetic pesticides can induce environmental pollution as well as the emergence of unpredictable new pest species. As plants cannot migrate to other locations on their own to combat various stresses, the production of secondary metabolites allows plants to protect themselves from stress and tolerate their reproduction. Pesticides using natural products are currently being developed to prevent environmental pollution and ecosystem disturbance caused by synthetic pesticides. In this study, after BPH infection in rice, chrysoeriol7 (C7), a secondary metabolite that induces resistance against BPH, was assessed. After C7 treatment and BPH infection, relative expression levels of the flavonoid-related genes were elevated, suggesting that in plants subjected to BPH, compounds related to flavonoids, among the secondary metabolites, play an important role in inducing resistance. The plant-derived natural compound chrysoeriol7 can potentially thus be used to develop environmentally friendly pesticides. The suggested control of BPH can be effectively used to alleviate concerns regarding environmental pollution and to construct a relatively safe rice breeding environment.

ERF Transcription Factor OsBIERF3 Positively Contributes to Immunity against Fungal and Bacterial Diseases but Negatively Regulates Cold Tolerance in Rice

We previously showed that overexpression of the rice ERF transcription factor gene OsBIERF3 in tobacco increased resistance against different pathogens. Here, we report the function of OsBIERF3 in rice immunity and abiotic stress tolerance. Expression of OsBIERF3 was induced by Xanthomonas oryzae pv. oryzae, hormones (e.g., salicylic acid, methyl jasmonate, 1-aminocyclopropane-1-carboxylic acid, and abscisic acid), and abiotic stress (e.g., drought, salt and cold stress). OsBIERF3 has transcriptional activation activity that depends on its C-terminal region. The OsBIERF3-overexpressing (OsBIERF3-OE) plants exhibited increased resistance while OsBIERF3-suppressed (OsBIERF3-Ri) plants displayed decreased resistance to Magnaporthe oryzae and X. oryzae pv. oryzae. A set of genes including those for PRs and MAPK kinases were up-regulated in OsBIERF3-OE plants. Cell wall biosynthetic enzyme genes were up-regulated in OsBIERF3-OE plants but down-regulated in OsBIERF3-Ri plants; accordingly, cell walls became thicker in OsBIERF3-OE plants but thinner in OsBIERF3-Ri plants than WT plants. The OsBIERF3-OE plants attenuated while OsBIERF3-Ri plants enhanced cold tolerance, accompanied by altered expression of cold-responsive genes and proline accumulation. Exogenous abscisic acid and 1-aminocyclopropane-1-carboxylic acid, a precursor of ethylene biosynthesis, restored the attenuated cold tolerance in OsBIERF3-OE plants while exogenous AgNO₃, an inhibitor of ethylene action, significantly suppressed the enhanced cold tolerance in OsBIERF3-Ri plants. These data demonstrate that OsBIERF3 positively contributes to immunity against M. oryzae and X. oryzae pv. oryzae but negatively regulates cold stress tolerance in rice.

Rice functional genomics: decades' efforts and roads ahead

Rice (Oryza sativa L.) is one of the most important crops in the world. Since the completion of rice reference genome sequences, tremendous progress has been achieved in understanding the molecular mechanisms on various rice traits and dissecting the underlying regulatory networks. In this review, we summarize the research progress of rice biology over past decades, including omics, genome-wide association study, phytohormone action, nutrient use, biotic and abiotic responses, photoperiodic flowering, and reproductive development (fertility and sterility). For the roads ahead, cutting-edge technologies such as new genomics methods, high-throughput phenotyping platforms, precise genome-editing tools, environmental microbiome optimization, and synthetic methods will further extend our understanding of unsolved molecular biology questions in rice, and facilitate integrations of the knowledge for agricultural applications.

Silencing a Simple Extracellular Leucine-Rich Repeat Gene OsI-BAK1 Enhances the Resistance of Rice to Brown Planthopper Nilaparvata lugens

Many plant proteins with extracellular leucine-rich repeat (eLRR) domains play an important role in plant immunity. However, the role of one class of eLRR plant proteins—the simple eLRR proteins—in plant defenses against herbivores remains largely unknown. Here, we found that a simple eLRR protein OsI-BAK1 in rice localizes to the plasma membrane. Its expression was induced by mechanical wounding, the infestation of gravid females of brown planthopper (BPH) Nilaparvata lugens or white-backed planthopper Sogatella furcifera and treatment with methyl jasmonate or abscisic acid. Silencing OsI-BAK1 (ir-ibak1) in rice enhanced the BPH-induced transcript levels of three defense-related WRKY genes (OsWRKY24, OsWRKY53 and OsWRKY70) but decreased the induced levels of ethylene. Bioassays revealed that the hatching rate was significantly lower in BPH eggs laid on ir-ibak1 plants than wild-type (WT) plants; moreover, gravid BPH females preferred to oviposit on WT plants over ir-ibak1 plants. The exogenous application of ethephon on ir-ibak1 plants eliminated the BPH oviposition preference between WT and ir-ibak1 plants but had no effect on the hatching rate of BPH eggs. These findings suggest that OsI-BAK1 acts as a negative modulator of defense responses in rice to BPH and that BPH might exploit this modulator for its own benefit.

A tomato receptor-like cytoplasmic kinase, SlZRK1, acts as a negative regulator in wound-induced jasmonic acid accumulation and insect resistance

Jasmonates accumulate rapidly and act as key regulators in response to mechanical wounding, but few studies have linked receptor-like cytoplasmic kinases (RLCKs) to wound-induced jasmonic acid (JA) signaling cascades. Here, we identified a novel wounding-induced RLCK-XII-2 subfamily member (SlZRK1) in tomato (Solanum lycopersicum) that was closely related to Arabidopsis HOPZ-ETI-DEFICIENT 1 (ZED1)-related kinases 1 based on phylogenetic analysis. SlZRK1 was targeted to the plasma membrane of tobacco mesophyll protoplasts as determined by transient co-expression with the plasma membrane marker mCherry-H+-ATPase. Catalytic residue sequence analysis and an in vitro kinase assay indicated that SlZRK1 may act as a pseudokinase. To further analyse the function of SlZRK1, we developed two stable knock-out mutants by CRISPR/Cas9. Loss of SlZRK1 significantly altered the expression of genes involved in JA biosynthesis, salicylic acid biosynthesis, and ethylene response. Furthermore, after mechanical wounding treatment, slzrk1 mutants increased transcription of early wound-inducible genes involved in JA biosynthesis and signaling. In addition, JA accumulation after wounding and plant resistance to herbivorous insects also were enhanced. Our findings expand plant regulatory networks in the wound-induced JA production by adding RLCKs as a new component in the wound signal transduction pathway.

Endophytic Strain Bacillus subtilis 26D Increases Levels of Phytohormones and Repairs Growth of Potato Plants after Colorado Potato Beetle Damage

Plant damage caused by defoliating insects has a long-term negative effect on plant growth and productivity. Consequently, the restoration of plant growth after exposure to pathogens or pests is the main indicator of the effectiveness of the implemented defense reactions. A short-term Leptinotarsa decemlineata Say attack on potato tube-grown plantlets (Solanum tuberosum L.) led to a reduction of both the length and mass of the shoots in 9 days. The decrease of the content of phytohormones—indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin and zeatin–riboside—in shoots of damaged potato plants was found. Endophytic strain Bacillus subtilis 26D (Cohn) is capable of secreting up to 83.6 ng/mL IAA and up to 150 ng/mL cytokinins into the culture medium. Inoculation of potato plants with cells of the B. subtilis 26D increases zeatin–riboside content in shoots and the mass of roots of undamaged plants, but does not influence content of IAA and ABA and growth of shoots. The presence of B. subtilis 26D in plant tissues promoted a rapid recovery of the growth rates of shoots, as well as the wet and dry mass of roots of plants after the pest attack, which we associate with the maintenance of a high level of IAA, ABA and cytokinins in their tissues.

Update on the Roles of Rice MAPK Cascades

The mitogen-activated protein kinase (MAPK) cascades have been validated playing critical roles in diverse aspects of plant biology, from growth and developmental regulation, biotic and abiotic stress responses, to phytohormone signal transduction or responses. A classical MAPK cascade consists of a MAPK kinase kinase (MAPKKK), a MAPK kinase (MAPKK), and a MAPK. From the 75 MAPKKKs, eight MAPKKs, and 15 MAPKs of rice, a number of them have been functionally deciphered. Here, we update recent advances in knowledge of the roles of rice MAPK cascades, including their components and complicated action modes, their diversified functions controlling rice growth and developmental responses, coordinating resistance to biotic and abiotic stress, and conducting phytohormone signal transduction. Moreover, we summarize several complete MAPK cascades that harbor OsMAPKKK-OsMAPKK-OsMAPK, their interaction with different upstream components and their phosphorylation of diverse downstream substrates to fulfill their multiple roles. Furthermore, we state a comparison of networks of rice MAPK cascades from signal transduction crosstalk to the precise selection of downstream substrates. Additionally, we discuss putative concerns for elucidating the underlying molecular mechanisms and molecular functions of rice MAPK cascades in the future.

OrMKK3 Influences Morphology and Grain Size in Rice

Although morphology and grain size are important to rice growth and yield, the identity of abundant natural allelic variations that determine agronomically important differences in crops is unknown. Here, we characterized the function of mitogen-activated protein kinase 3 from Oryza officinalis Wall. ex Watt encoded by OrMKK3. Different alternative splicing variants occurred in OrMKK3. Green fluorescent protein (GFP)-OrMKK3 fusion proteins localized to the cell membrane and nuclei of rice protoplasts. Overexpression of OrMKK3 influenced the expression levels of the grain size-related genes SMG1, GW8, GL3, GW2, and DEP3. Phylogenetic analysis showed that OrMKK3 is well conserved in plants while showing large amounts of variation between indica, japonica, and wild rice. In addition, OrMKK3 slightly influenced brassinosteroid (BR) responses and the expression levels of BR-related genes. Our findings thus identify a new gene, OrMKK3, influencing morphology and grain size and that represents a possible link between mitogen-activated protein kinase and BR response pathways in grain growth.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12374-020-09290-2.

Overexpression of a Cytosolic 6-Phosphogluconate Dehydrogenase Gene Enhances the Resistance of Rice to Nilaparvata lugens

The pentose phosphate pathway (PPP) plays an important role in plant growth and development, and plant responses to biotic and abiotic stresses. Yet, whether the PPP regulates plant defenses against herbivorous insects remains unclear. In this study, we cloned a rice cytosolic 6-phosphogluconate dehydrogenase gene, Os6PGDH1, which encodes the key enzyme catalyzing the third step in the reaction involving the oxidative phase of the PPP, and explored its role in rice defenses induced by brown planthopper (BPH) Nilaparvata lugens. Levels of Os6PGDH1 transcripts were detected in all five examined tissues, with the highest in outer leaf sheaths and lowest in inner leaf sheaths. Os6PGDH1 expression was strongly induced by mechanical wounding, infestation of gravid BPH females, and jasmonic acid (JA) treatment. Overexpressing Os6PGDH1 (oe6PGDH) decreased the height of rice plants and the mass of the aboveground part of plants, but slightly increased the length of plant roots. In addition, the overexpression of Os6PGDH1 enhanced levels of BPH-induced JA, jasmonoyl-isoleucine (JA-Ile), and H₂O₂, but decreased BPH-induced levels of ethylene. Bioassays revealed that gravid BPH females preferred to feed and lay eggs on wild-type (WT) plants over oe6PGDH plants; moreover, the hatching rate of BPH eggs raised on oe6PGDH plants and the fecundity of BPH females fed on these were significantly lower than the eggs and the females raised and fed on WT plants. Taken together, these results indicate that Os6PGDH1 plays a pivotal role not only in rice growth but also in the resistance of rice to BPH by modulating JA, ethylene, and H₂O₂ pathways.

Research Progress on Oviposition-Related Genes in Insects

Oviposition-related genes have remained a consistent focus of insect molecular biology. Previous research has gradually clarified our mechanistic understanding of oviposition-related genes, including those related to oviposition-gland-related genes, oogenesis-related genes, oviposition-site-selection-related genes, and genes related to ovulation and hatching. Moreover, some of this research has revealed how the expression of single oviposition-related genes affects the expression of related genes, and more importantly, how individual node genes function to link the expression of upstream and downstream genes. However, the research to date is not sufficient to completely explain the overall interactions among the genes of the insect oviposition system. Through a literature review of a large number of studies, this review provides references for future research on oviposition-related genes in insects and the use of RNAi or CRISPR/Cas9 technology to verify the functions of oviposition-related genes and to prevent and control harmful insects.

Suppression of a leucine-rich repeat receptor-like kinase enhances host plant resistance to a specialist herbivore

The mechanisms by which herbivores induce plant defenses are well studied. However, how specialized herbivores suppress plant resistance is still poorly understood. Here, we discovered a rice (Oryza sativa) leucine-rich repeat receptor-like kinase, OsLRR-RLK2, which is induced upon attack by gravid females of a specialist piercing-sucking herbivore, the brown planthopper (BPH, Nilaparvata lugens). Silencing OsLRR-RLK2 decreases the constitutive activity of mitogen-activated protein kinase (OsMPK6) and alters BPH-induced transcript levels of several defense-related WRKY transcription factors. Moreover, silencing OsLRR-RLK2 reduces BPH-induction of jasmonic acid and ethylene but promotes the biosynthesis of both elicited salicylic acid and H₂ O₂ ; silencing also enhances the production of volatiles emitted from rice plants infested with gravid BPH females. These changes decrease BPH preference and performance in the glasshouse and the field. These findings suggest that OsLRR-RLK2, by regulating the plant's defense-related signaling profile, increases the susceptibility of rice to BPH, and that BPH infestation influences the expression of OsLRR-RLK2, suppressing the resistance of rice to BPH.

Exogenous jasmonic acid decreased Cu accumulation by alfalfa and improved its photosynthetic pigments and antioxidant system

Jasmonic acid (JA) is an important phytohormone, which among others may be involved in the regulation of plant accumulating heavy metal. This experiment was designed to explore the effects of exogenous JA on the responses of alfalfa to Cu stress (100 μM) in Hoagland solution. When 1, 5 or 10 mM JA was added to the treatment with Cu addition, Cu concentrations in roots and leaves of alfalfa were significantly decreased (p < 0.05) to some extents compared to the treatment without JA addition. The biomasses of roots and leaves of alfalfa in treatments of JA additions were significantly increased (p < 0.05) compared to the Cu stress treatment. Similarly, the concentrations of Chlorophyll, antioxidant enzyme activities, MDA and H₂O₂ were improved accordingly. But these factors of JA were not improved further when its concentration added in media was the highest (10 mM), indicating its improvement roles were limited. These results suggested that there were positive roles of exogenous JA on alfalfa decreased its Cu accumulation and toxicities might via reduced oxidative stress.

Plant-insect-microbe interaction: A love triangle between enemies in ecosystem

In natural ecosystems, plants interact with biotic components such as microbes, insects, animals and other plants as well. Generally, researchers have focused on each interaction separately, which condenses the significance of the interaction. This limited presentation of the facts masks the collective role of constantly interacting organisms in complex communities disturbing not only plant responses but also the response of organisms for each other in natural ecological settings. Beneficial microorganisms interact with insect herbivores, their predators and pollinators in a bidirectional way through the plant. Fascinatingly, insects employ diverse tactics to protect themselves from parasites or predators. Influences of microbial and insects attack on plants can bring changes in info-chemical frameworks and play a role in the food chain also. After insect herbivory and microbial pathogenesis, plants exhibit intense morpho-physiological and chemical reprogramming that leads to repellence/attraction of attacking organism or its natural enemy. The characterization of such interactions in different ecosystems is receiving due consideration, and underlying molecular and physiological mechanisms must be the point of concentration to unveil the evolution of multifaceted multitrophic interactions. Therefore, we have focused this phenomenon in a more realistic setting by integrating ecology and physiology to portray these multidimensional interfaces. We have shown, in this article, physiological trajectories in plant-microbe and insect relationship and their ecological relevance in nature. We focus and discuss microbial pathogenesis in plants, induced defense and the corresponding behavior of herbivore insects and vice-versa. It is hoped that this review will stimulate interest and zeal in microbes mediated plant-insect interactions along with their ecological consequences and encourage scientists to accept the challenges in this field.

Two splice variants of the DsMEK1 mitogen-activated protein kinase kinase (MAPKK) are involved in salt stress regulation in Dunaliella salina in different ways

BACKGROUND

Dunaliella salina can produce glycerol under salt stress, and this production can quickly adapt to changes in external salt concentration. Notably, glycerol is an ideal energy source. In recent years, it has been reported that the mitogen-activated protein kinase cascade pathway plays an important role in regulating salt stress, and in Dunaliella tertiolecta DtMAPK can regulate glycerol synthesis under salt stress. Therefore, it is highly important to study the relationship between the MAPK cascade pathway and salt stress in D. salina and modify it to increase the production of glycerol.

RESULTS

In our study, we identified and analysed the alternative splicing of DsMEK1 (DsMEK1-X1, DsMEK1-X2) from the unicellular green alga D. salina. DsMEK1-X1 and DsMEK1-X2 were both localized in the cytoplasm. qRT-PCR assays showed that DsMEK1-X2 was induced by salt stress. Overexpression of DsMEK1-X2 revealed a higher increase rate of glycerol production compared to the control and DsMEK1-X1-oe under salt stress. Under salt stress, the expression of DsGPDH2/3/5/6 increased in DsMEK1-X2-oe strains compared to the control. This finding indicated that DsMEK1-X2 was involved in the regulation of DsGPDH expression and glycerol overexpression under salt stress. Overexpression of DsMEK1-X1 increased the proline content and reduced the MDA content under salt stress, and DsMEK1-X1 was able to regulate oxidative stress; thus, we hypothesized that DsMEK1-X1 could reduce oxidative damage under salt stress. Yeast two-hybrid analysis showed that DsMEK1-X2 could interact with DsMAPKKK1/2/3/9/10/17 and DsMAPK1; however, DsMEK1-X1 interacted with neither upstream MAPKKK nor downstream MAPK. DsMEK1-X2-oe transgenic lines increased the expression of DsMAPKKK1/3/10/17 and DsMAPK1, and DsMEK1-X2-RNAi lines decreased the expression of DsMAPKKK2/10/17. DsMEK1-X1-oe transgenic lines did not exhibit increased gene expression, except for DsMAPKKK9.

CONCLUSION

Our findings demonstrate that DsMEK1-X1 and DsMEK1-X2 can respond to salt stress by two different pathways. The DsMEK1-X1 response to salt stress reduces oxidative damage; however, the DsMAPKKK1/2/3/9/10/17-DsMEK1-X2-DsMAPK1 cascade is involved in the regulation of DsGPDH expression and thus glycerol synthesis under salt stress.