Jasmonate-induced defenses: a tale of intelligence, collaborators and rascals

Leafhopper salivary carboxylesterase suppresses JA-Ile synthesis to facilitate initial arbovirus transmission in rice phloem

Plant jasmonoyl-L-isoleucine (JA-Ile) is a major defense signal against insect feeding, but whether or how insect salivary effectors suppress JA-Ile synthesis and thus facilitate viral transmission in the plant phloem remains elusive. Insect carboxylesterases (CarEs) are the third major family of detoxification enzymes. Here, we identify a new leafhopper CarE, CarE10, that is specifically expressed in salivary glands and is secreted into the rice phloem as a saliva component. Leafhopper CarE10 directly binds to rice jasmonate resistant 1 (JAR1) and promotes its degradation by the proteasome system. Moreover, the direct association of CarE10 with JAR1 clearly impairs JAR1 enzyme activity for conversion of JA to JA-Ile in an in vitro JA-Ile synthesis system. A devastating rice reovirus activates and promotes the co-secretion of virions and CarE10 via virus-induced vesicles into the saliva-storing salivary cavities of the leafhopper vector and ultimately into the rice phloem to establish initial infection. Furthermore, a virus-mediated increase in CarE10 secretion or overexpression of CarE10 in transgenic rice plants causes reduced levels of JAR1 and thus suppresses JA-Ile synthesis, promoting host attractiveness to insect vectors and facilitating initial viral transmission. Our findings provide insight into how the insect salivary protein CarE10 suppresses host JA-Ile synthesis to promote initial virus transmission in the rice phloem.

Valsa mali PR1-like protein modulates an apple valine-glutamine protein to suppress JA signaling-mediated immunity

Apple Valsa canker (AVC) is a devastating disease of apple (Malus × domestica), caused by Valsa mali (Vm). The Cysteine-rich secretory protein, Antigen 5, and Pathogenesis-related protein 1 (CAP) superfamily protein PATHOGENESIS-RELATED PROTEIN 1-LIKE PROTEIN c (VmPR1c) plays an important role in the pathogenicity of Vm. However, the mechanisms through which it exerts its virulence function in Vm-apple interactions remain unclear. In this study, we identified an apple valine-glutamine (VQ)-motif-containing protein, MdVQ29, as a VmPR1c target protein. MdVQ29-overexpressing transgenic apple plants showed substantially enhanced AVC resistance as compared with the wild type. MdVQ29 interacted with the transcription factor MdWRKY23, which was further shown to bind to the promoter of the jasmonic acid (JA) signaling-related gene CORONATINE INSENSITIVE 1 (MdCOI1) and activate its expression to activate the JA signaling pathway. Disease evaluation in lesion areas on infected leaves showed that MdVQ29 positively modulated apple resistance in a MdWRKY23-dependent manner. Furthermore, MdVQ29 promoted the transcriptional activity of MdWRKY23 toward MdCOI1. In addition, VmPR1c suppressed the MdVQ29-enhanced transcriptional activation activity of MdWRKY23 by promoting the degradation of MdVQ29 and inhibiting MdVQ29 expression and the MdVQ29-MdWRKY23 interaction, thereby interfering with the JA signaling pathway and facilitating Vm infection. Overall, our results demonstrate that VmPR1c targets MdVQ29 to manipulate the JA signaling pathway to regulate immunity. Thus, this study provides an important theoretical basis and guidance for mining and utilizing disease-resistance genetic resources for genetically improving apples.

Salicylic acid inducing the expression of maize anti-insect gene SPI: a potential control strategy for Ostrinia furnacalis

BACKGROUND

Due to being rooted in the ground, maize (Zea mays L.) is unable to actively escape the attacks of herbivorous insects such as the Asian corn borer (Ostrinia furnacalis). In contrast to the passive damage, plants have evolved defense mechanisms to protect themselves from herbivores. Salicylic acid, a widely present endogenous hormone in plants, has been found to play an important role in inducing plant resistance to insects. In this study, we screened and identified the insect resistance gene SPI, which is simultaneously induced by SA and O. furnacalis feeding, through preliminary transcriptome data analysis. The functional validation of SPI was carried out using bioinformatics, RT-qPCR, and heterologous expression protein feeding assays.

RESULTS

Both SA and O. furnacalis treatment increased the expression abundance of SA-synthesis pathway genes and SPI in three maize strains, and the upregulation of SPI was observed strongly at 6 hours post-treatment. The expression of SPI showed a temporal relationship with SA pathway genes, indicating that SPI is a downstream defense gene regulated by SA. Protein feeding assays using two different expression vectors demonstrated that the variation in SPI protein activity among different strains is mainly due to protein modifications.

CONCLUSIONS

Our research results indicate that SPI, as a downstream defense gene regulated by SA, is induced by SA and participates in maize's insect resistance. The differential expression levels of SPI gene and protein modifications among different maize strains are one of the reasons for the variation in insect resistance. This study provides new insights into ecological pest control in maize and valuable insights into plant responses to SA-induced insect resistance.

Autophagy promotes jasmonate-mediated defense against nematodes

Autophagy, as an intracellular degradation system, plays a critical role in plant immunity. However, the involvement of autophagy in the plant immune system and its function in plant nematode resistance are largely unknown. Here, we show that root-knot nematode (RKN; Meloidogyne incognita) infection induces autophagy in tomato (Solanum lycopersicum) and different atg mutants exhibit high sensitivity to RKNs. The jasmonate (JA) signaling negative regulators JASMONATE-ASSOCIATED MYC2-LIKE 1 (JAM1), JAM2 and JAM3 interact with ATG8s via an ATG8-interacting motif (AIM), and JAM1 is degraded by autophagy during RKN infection. JAM1 impairs the formation of a transcriptional activation complex between ETHYLENE RESPONSE FACTOR 1 (ERF1) and MEDIATOR 25 (MED25) and interferes with transcriptional regulation of JA-mediated defense-related genes by ERF1. Furthermore, ERF1 acts in a positive feedback loop and regulates autophagy activity by transcriptionally activating ATG expression in response to RKN infection. Therefore, autophagy promotes JA-mediated defense against RKNs via forming a positive feedback circuit in the degradation of JAMs and transcriptional activation by ERF1.

Characterization of sandalwood (E,E)-α-farnesene synthase whose overexpression enhances cold tolerance through jasmonic acid biosynthesis and signaling in Arabidopsis

MAIN CONCLUSION

Santalum album (E,E)-α-farnesene synthase catalyzes FPP into (E,E)-α-farnesene. Overexpression of the SaAFS gene positively improved cold stress tolerance through JA biosynthesis and signaling pathways in Arabidopsis. Volatile terpenoids are released from plants that suffer negative effects following exposure to various biotic and abiotic stresses. Recent studies revealed that (E,E)-α-farnesene synthase (AFS) plays a significant role in a plant's defence against biotic attack. However, little is known about whether AFS contributes to plant resistance to cold stress. In this study, a SaAFS gene was isolated from Indian sandalwood (Santalum album L.) and functionally characterized. The SaAFS protein mainly converts farnesyl diphosphate to (E,E)-α-farnesene. SaAFS was clustered into the AFS clade from angiosperms, suggesting a highly conserved enzyme. SaAFS displayed a significant response to cold stress and methyl jasmonate. SaAFS overexpression (OE) in Arabidopsis enhanced cold tolerance by increasing proline content, reducing malondialdehyde content, electrolyte leakage, and accumulating reactive oxygen species. Transcriptomic analysis revealed that upregulated genes related to stress response and JA biosynthesis and signaling were detected in SaAFS-OE lines compared with wild type plants that were exposed to cold stress. Endogenous JA and jasmonoyl-isoleucine content increased significantly in SaAFS-OE lines exposed to cold stress. Collectively considered, these results suggest that the SaAFS gene is a positive regulator during cold stress tolerance via JA biosynthesis and signaling pathways.

Attackers gain the upper hand over plants in the face of rapid global change

Interactions among organisms in natural ecosystems are the foundational underpinnings of nearly all ecological studies. It has never been more important to increase our awareness of how these interactions are altered by human activity, threatening biodiversity and disrupting ecosystem functioning. Much of the historic focus of species conservation has been the preservation of endangered and endemic species at risk from hunting, over-exploitation, and habitat destruction. However, there is increasing evidence that differences between plants and their attacking organisms in the speed and direction of physiological, demographic, and genetic (adaptation) responses to global change are having devastating consequences, resulting in large-scale losses of dominant or abundant plant species, particularly in forest ecosystems. From the elimination in the wild of the American chestnut to the extensive regional damage caused by insect outbreaks in temperate forest ecosystems, these losses of dominant species change the ecological landscape and functioning, and represent important threats to biodiversity at all scales. Introductions due to human activity, range shifts due to climate change, and their combination are the principal drivers behind these profound ecosystem changes. In this Review, we argue that there is an urgent need to increase our recognition and hone our predictive power for how these imbalances may occur. Moreover, we should seek to minimize the consequences of these imbalances in order to ensure the preservation of the structure, function and biodiversity of entire ecosystems, not just rare or highly endangered species.

Cross-Kingdom Regulation of Plant-Derived miRNAs in Modulating Insect Development

MicroRNAs (miRNAs), a class of non-coding small RNAs, are crucial regulatory factors in plants and animals at the post-transcriptional level. These tiny molecules suppress gene expression by complementary oligonucleotide binding to sites in the target messenger. Recently, the discovery of plant-derived miRNAs with cross-kingdom abilities to regulate gene expression in insects has promoted exciting discussion, although some controversies exist regarding the modulation of insect development by plant-derived miRNAs. Here, we review current knowledge about the mechanisms of miRNA biogenesis, the roles of miRNAs in coevolution between insects and plants, the regulation of insect development by plant-derived miRNAs, the cross-kingdom transport mechanisms of plant-derived miRNAs, and cross-kingdom regulation. In addition, the controversy regarding the modulation of insect development by plant-derived miRNAs also was discussed. Our review provides new insights for understanding complex plant-insect interactions and discovering new strategies for pest management and even crop genetic improvement.

Plant Metabolomics: An Overview of the Role of Primary and Secondary Metabolites against Different Environmental Stress Factors

Several environmental stresses, including biotic and abiotic factors, adversely affect the growth and development of crops, thereby lowering their yield. However, abiotic factors, e.g., drought, salinity, cold, heat, ultraviolet radiations (UVr), reactive oxygen species (ROS), trace metals (TM), and soil pH, are extremely destructive and decrease crop yield worldwide. It is expected that more than 50% of crop production losses are due to abiotic stresses. Moreover, these factors are responsible for physiological and biochemical changes in plants. The response of different plant species to such stresses is a complex phenomenon with individual features for several species. In addition, it has been shown that abiotic factors stimulate multi-gene responses by making modifications in the accumulation of the primary and secondary metabolites. Metabolomics is a promising way to interpret biotic and abiotic stress tolerance in plants. The study of metabolic profiling revealed different types of metabolites, e.g., amino acids, carbohydrates, phenols, polyamines, terpenes, etc, which are accumulated in plants. Among all, primary metabolites, such as amino acids, carbohydrates, lipids polyamines, and glycine betaine, are considered the major contributing factors that work as osmolytes and osmoprotectants for plants from various environmental stress factors. In contrast, plant-derived secondary metabolites, e.g., phenolics, terpenoids, and nitrogen-containing compounds (alkaloids), have no direct role in the growth and development of plants. Nevertheless, such metabolites could play a significant role as a defense by protecting plants from biotic factors such as herbivores, insects, and pathogens. In addition, they can enhance the resistance against abiotic factors. Therefore, metabolomics practices are becoming essential and influential in plants by identifying different phytochemicals that are part of the acclimation responses to various stimuli. Hence, an accurate metabolome analysis is important to understand the basics of stress physiology and biochemistry. This review provides insight into the current information related to the impact of biotic and abiotic factors on variations of various sets of metabolite levels and explores how primary and secondary metabolites help plants in response to these stresses.

Herbivore-induced Ca2+ signals trigger a jasmonate burst by activating ERF16-mediated expression in tomato

Herbivory severely affects plant growth, posing a threat to crop production. Calcium ion (Ca²⁺ ) signaling and accumulation of jasmonates (JAs) are activated in plant response to herbivore attack, leading to the expression of defense pathways. However, little is known about how the Ca²⁺ signal modulates JA biosynthesis. We used diverse techniques, including CRISPR/Cas9, UPLC-MS/MS and molecular biology methods to explore the role of ETHYLENE RESPONSE FACTOR 16 in Ca²⁺ signal-triggered JA burst during herbivore defense in tomato. Here we show that simulated herbivory induces GLUTAMATE RECEPTOR LIKE3.3/3.5 (GLR3.3/3.5)-dependent increases in electrical activity, Ca²⁺ influx and increases the abundance of CALMODULIN2 (CaM2) and ERF16 transcripts in tomato. The interaction between CaM2 and ERF16 promotes JA biosynthesis by enhancing the transcriptional activity of ERF16, which increases the activation of ERF16 expression and causes expression of LIPOXYGENASE D (LOXD), AOC and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3 (OPR3), the key genes in JA biosynthesis. Mutation of CaM2 results in decreased JA accumulation, together with the expression of JA biosynthesis-related genes, leading to reduced resistance to the cotton bollworm Helicoverpa armigera. These findings reveal a molecular mechanism underpinning the Ca²⁺ signal-initiated systemic JA burst and emphasize the pivotal role of Ca²⁺ signal/ERF16 crosstalk in herbivore defense.

Study on the Suitability of Tea Cultivars for Processing Oolong Tea from the Perspective of Aroma Based on Olfactory Sensory, Electronic Nose, and GC-MS Data Correlation Analysis

The oolong tea aroma is shown to consist of cultivar aroma and technical aroma in this study based on the aroma differences between oolong tea products of cultivars of different suitability, as determined by correlation analysis of olfactory, sensory, electronic nose, and GC-MS data. Human senses were significantly affected by the aroma components, which included eight terpene metabolites (β-Ocimene, (Z)-Furan linalool oxide, linalool, (3E)-4,8-Dimethyl-1,3,7-nonatriene, (E)-Pyranoid linalool oxide, γ-Elemene, Humulene, (Z,E)-α-Farnesene), three carotenoid metabolites (β-Ionone, (Z)-Geranylacetone and 6-methyl-5-Hepten -2-one), three lipid metabolites ((Z)-3-Hexenyl (Z)-3-hexenoate, Butanoic acid hexyl ester, and (Z)-Jasmone), four amino acid metabolites (Methyl salicylate, Geranyl isovalerate, indole, and Phenylethyl alcohol), and six thermal reaction products (2-Pentylfuran, Octanal, Decanal, (E,E)-2,4-Nonadienal, (Z)-2-Decenal, and (E)-2-Undecenal). Meanwhile, several aroma compounds (such as (E)-Nerolidol and α-Farnesene), mainly comprising the “technical aroma” formed in the processing mode, were noted to be less closely related to cultivar suitability. This study sheds light on the aroma characteristics of different tea cultivars for oolong tea processing.

Disentangling the effects of jasmonate and tissue loss on the sex allocation of an annual plant

Selection through pollinators plays a major role in the evolution of reproductive traits. However, herbivory can also induce changes in plant sexual expression and sexual systems, potentially influencing conditions governing transitions between sexual systems. Previous work has shown that herbivory has a strong effect on sex allocation in the wind-pollinated annual plant Mercurialis annua, likely via responses to resource loss. It is also known that many plants respond to herbivory by inducing signaling, and endogenous responses to it, via the plant hormone jasmonate. Here, we attempt to uncouple the effects of herbivory on sex allocation in M. annua through resource limitation (tissue loss) versus plant responses to jasmonate hormone signaling. We used a two-factorial experiment with four treatment combinations: control, herbivory (25% chronic tissue loss), jasmonate, and combined herbivory and jasmonate. We estimated the effects of tissue loss and defense-inducing hormones on reproductive allocation, male reproductive effort, and sex allocation. Tissue loss caused plants to reduce their male reproductive effort, resulting in changes in total sex allocation. However, application of jasmonate after herbivory reversed its effect on male investment. Our results show that herbivory has consequences on plant sex expression and sex allocation, and that defense-related hormones such as jasmonate can buffer the impacts. We discuss the physiological mechanisms that might underpin the effects of herbivory on sex allocation, and their potential implications for the evolution of plant sexual systems.

Cytokinin Regulates Energy Utilization in Botrytis cinerea

The plant hormone cytokinin (CK) is an important developmental regulator. Previous work has demonstrated that CKs mediate plant immunity and disease resistance. Some phytopathogens have been reported to secrete CKs and may manipulate CK signaling to improve pathogenesis. In recent work, we demonstrated that CK directly inhibits the development and virulence of fungal phytopathogens by attenuating the cell cycle and reducing cytoskeleton organization. Here, focusing on Botrytis cinerea, we report that CK possesses a dual role in fungal biology, with role prioritization being based on sugar availability. In a sugar-rich environment, CK strongly inhibited B. cinerea growth and deregulated cytoskeleton organization. This effect diminished as sugar availability decreased. In its second role, we show using biochemical assays and transgenic redox-sensitive fungal lines that CK can promote glycolysis and energy consumption in B. cinerea, both in vitro and in planta. Glycolysis and increased oxidation mediated by CK were stronger in low sugar availability, indicating that sugar availability could indeed be one possible element determining the role of CK in the fungus. Transcriptomic data further support our findings, demonstrating significant upregulation to glycolysis, oxidative phosphorylation, and sucrose metabolism upon CK treatment. Thus, the effect of CK in fungal biology likely depends on energy status. In addition to the plant producing CK during its interaction with the pathogen for defense priming and pathogen inhibition, the pathogen may take advantage of this increased CK to boost its metabolism and energy production, in preparation for the necrotrophic phase of the infection.

IMPORTANCE The hormone cytokinin (CK) is a plant developmental regulator. Previous research has highlighted the involvement of CK in plant defense. Here, we report that CK has a dual role in plant-fungus interactions, inhibiting fungal growth while positively regulating B. cinerea energy utilization, causing an increase in glucose utilization and energy consumption. The effect of CK on B. cinerea was dependent on sugar availability, with CK primarily causing increases in glycolysis when sugar availability was low, and growth inhibition in a high-sugar environment. We propose that CK acts as a signal to the fungus that plant tissue is present, causing it to activate energy metabolism pathways to take advantage of the available food source, while at the same time, CK is employed by the plant to inhibit the attacking pathogen.

Impact of Future Elevated Carbon Dioxide on C3 Plant Resistance to Biotic Stresses

Before the end of the century, atmospheric carbon dioxide levels are predicted to increase to approximately 900 ppm. This will dramatically affect plant physiology and influence environmental interactions and, in particular, plant resistance to biotic stresses. This review is a broad survey of the current research on the effects of elevated CO₂ (eCO₂) on phytohormone-mediated resistance of C₃ agricultural crops and related model species to pathogens and insect herbivores. In general, while plants grown in eCO₂ often have increased constitutive and induced salicylic acid levels and suppressed induced jasmonate levels, there are exceptions that implicate other environmental factors, such as light and nitrogen fertilization in modulating these responses. Therefore, this review sets the stage for future studies to delve into understanding the mechanistic basis behind how eCO₂ will affect plant defensive phytohormone signaling pathways under future predicted environmental conditions that could threaten global food security to inform the best agricultural management practices.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Identification of genes associated with biosynthesis of bioactive flavonoids and taxoids in Taxus cuspidata Sieb. et Zucc. plantlets exposed to UV-B radiation

UV-B radiation is a typical environmental stressor that can promote phytochemical accumulation in plants. Taxus species are highly appreciated due to the existence of bioactive taxoids (especially paclitaxel) and flavonoids. However, the effect of UV-B radiation on taxoid and flavonoid biosynthesis in Taxus cuspidata Sieb. et Zucc. is largely unknown. In the present work, the accumulation of taxoids and flavonoids in T. cuspidata plantlets was significantly induced by 12 and 24 h of UV-B radiation (3 W/m²), and a large number of significantly differentially expressed genes were obtained via transcriptomic analysis. The significant up-regulation of antioxidant enzyme- and flavonoid biosynthesis-related genes (phenylalanine ammonia lyase 1, chalcone synthase 2, flavonol synthase 1, and flavonoid 3', 5'-hydroxylase 2), suggested that UV-B might cause the oxidative stress thus promoting flavonoid accumulation in T. cuspidata. Moreover, the expression of some genes related to jasmonate metabolism and taxoid biosynthesis (taxadiene synthase, baccatin III-3-amino 3-phenylpropanoyltransferase 1, taxadiene-5α-hydroxylase, and ethylene response factors 15) was significantly activated, which indicated that UV-B might initiate jasmonate signaling pathway that contributed to taxoid enhancement in T. cuspidata. Additionally, the identification of some up-regulated genes involved in lignin biosynthesis pathway indicated that the lignification process in T. cuspidata might be stimulated for defense against UV-B radiation. Overall, our findings provided a better understanding of some potential key genes associated with flavonoid and taxoid biosynthesis in T. cuspidata exposed to UV-B radiation.

Priming Seeds with Indole and (Z)-3-Hexenyl Acetate Enhances Resistance Against Herbivores and Stimulates Growth

A striking feature of plant ecology is the ability of plants to detect and respond to environmental cues such as herbivore-induced plant volatiles (HIPVs) by priming or directly activating defenses against future herbivores. However, whether seeds also respond to compounds that are common constituents of HIPV blends and initiate future plant resistance is unknown. Considering that seeds depend on other environmental cues to determine basic survival traits such as germination timing, we predicted that seeds exposed to synthetic constituents of HIPV blends would generate well-defended plants. We investigated the effect of seed exposure to common volatiles on growth, reproduction, and resistance characteristics in the model plants Arabidopsis thaliana and Medicago truncatula using herbivores from two feeding guilds. After seed scarification and vernalization, we treated seeds with one of seven different plant-derived volatile compounds for 24 h. Seeds were then germinated and the resulting plants were assayed for growth, herbivore resistance, and expression of inducible defense genes. Of all the synthetic volatiles tested, indole specifically reduced both beet armyworm growth on A. thaliana and pea aphid fecundity on M. truncatula. The induction of defense genes was not affected by seed exposure to indole in either plant species, indicating that activation of direct resistance rather than inducible resistance is the mechanism by which seed priming operates. Moreover, neither plant species showed any negative effect of seed exposure to any synthetic volatile on vegetative and reproductive growth. Rather, M. truncatula plants derived from seeds exposed to (Z)-3-hexanol and (Z)-3-hexenyl acetate grew larger compared to controls. Our results indicate that seeds are sensitive to specific volatiles in ways that enhance resistance profiles with no apparent costs in terms of growth. Seed priming by HIPVs may represent a novel ecological mechanism of plant-to-plant interactions, with broad potential applications in agriculture and seed conservation.

Multi-Omics-Based Discovery of Plant Signaling Molecules

Plants produce numerous structurally and functionally diverse signaling metabolites, yet only relatively small fractions of which have been discovered. Multi-omics has greatly expedited the discovery as evidenced by increasing recent works reporting new plant signaling molecules and relevant functions via integrated multi-omics techniques. The effective application of multi-omics tools is the key to uncovering unknown plant signaling molecules. This review covers the features of multi-omics in the context of plant signaling metabolite discovery, highlighting how multi-omics addresses relevant aspects of the challenges as follows: (a) unknown functions of known metabolites; (b) unknown metabolites with known functions; (c) unknown metabolites and unknown functions. Based on the problem-oriented overview of the theoretical and application aspects of multi-omics, current limitations and future development of multi-omics in discovering plant signaling metabolites are also discussed.

Simulated herbivory enhances leaky sex expression in the dioecious herb Mercurialis annua

BACKGROUND AND AIMS

Plant reproductive traits are widely understood to be responsive to the selective pressures exerted by pollinators, but there is also increasing evidence for an important role for antagonists such as herbivores in shaping these traits. Many dioecious species show leaky sex expression, with males and females occasionally producing flowers of the opposite sex. Here, we asked to what extent leakiness in sex expression in Mercurialis annua (Euphorbiaceae) might also be plastically responsive to simulated herbivory. This is important because enhanced leakiness in dioecious populations could lead to a shift in both the mating system and in the conditions for transitions between combined and separate sexes.

METHODS

We examined the effect of simulated herbivory on the sexual expression of males and females of M. annua in two experiments in which different levels of simulated herbivory led to enhanced leakiness in both sexes.

KEY RESULTS

We showed that leaky sex expression in both males and females of the wind-pollinated dioecious herb M. annua is enhanced in response to simulated herbivory, increasing the probability for and the degree of leakiness in both sexes. We also found that leakiness was greater in larger females but not in larger males.

CONCLUSIONS

We discuss hypotheses for a possible functional link between herbivory and leaky sex expression, and consider what simulated herbivory-induced leakiness might imply for the evolutionary ecology of plant reproductive systems, especially the breakdown of dioecy and the evolution of hermaphroditism.

Cytokinin Inhibits Fungal Development and Virulence by Targeting the Cytoskeleton and Cellular Trafficking

Cytokinin (CK) is an important plant developmental regulator, having activities in many aspects of plant life and response to the environment. CKs are involved in diverse processes in the plant, including stem cell maintenance, vascular differentiation, growth and branching of roots and shoots, leaf senescence, nutrient balance, and stress tolerance. In some cases, phytopathogens secrete CKs. It has been suggested that to achieve pathogenesis in the host, CK-secreting biotrophs manipulate CK signaling to regulate the host cell cycle and nutrient allocation. CK is known to induce host plant resistance to several classes of phytopathogens from a few works, with induced host immunity via salicylic acid signaling suggested to be the prevalent mechanism for this host resistance. Here, we show that CK directly inhibits the growth, development, and virulence of fungal phytopathogens. Focusing on Botrytis cinerea (Bc), we demonstrate that various aspects of fungal development can be reversibly inhibited by CK. We also found that CK affects both budding and fission yeast in a similar manner. Investigating the mechanism by which CK influences fungal development, we conducted RNA next-generation sequencing (RNA-NGS) on mock- and CK-treated B. cinerea samples, finding that CK alters the cell cycle, cytoskeleton, and endocytosis. Cell biology experiments demonstrated that CK affects cytoskeleton components and cellular trafficking in Bc, lowering endocytic rates and endomembrane compartment sizes, likely leading to reduced growth rates and arrested developmental programs. Mutant analyses in yeast confirmed that the endocytic pathway is altered by CK. Our work uncovers a remarkably conserved role for a plant growth hormone in fungal biology, suggesting that pathogen-host interactions resulted in fascinating molecular adaptations on fundamental processes in eukaryotic biology.

Herbivory and jasmonate treatment affect reproductive traits in wild Lima bean, but without transgenerational effects

PREMISE

Plant responses to herbivores and their elicitors include changes in traits associated with phenology, defense, and reproduction. Induced responses by chewing herbivores are known to be hormonally mediated by the jasmonate pathway and can cascade and affect late-season seed predators and pollinators. Moreover, herbivore-induced plant responses can be transmitted to the next generation. Whether herbivore-induced transgenerational effects also apply to phenological traits is less well understood.

METHODS

Here, we explored responses of wild lima bean plants (Phaseolus lunatus) to herbivory and jasmonate treatment and possible transgenerational effects of herbivore-induced early flowering. In a controlled field experiment, we exposed lima bean plants to herbivory by leaf beetles or methyl jasmonate sprays (MJ). We then compared plant development, phenology, reproductive fitness and seed traits among these treatments and undamaged, untreated control plants.

RESULTS

We found that MJ and leaf herbivory induced similar responses, with treated plants growing less, flowering earlier, and producing fewer seeds than undamaged plants. However, seed size, phenolics and cyanogenic glycosides concentrations did not differ among treatments. Seed germination rates and flowering time of the offspring were similar among maternal treatments.

CONCLUSIONS

Overall, the results confirm that responses of lima bean to herbivory by leaf beetles are mediated by jasmonate; however, effects on phenological traits are not transmitted to the next generation. We discuss why transgenerational effects of herbivory might be restricted to traits that directly target herbivores.

Exogenous salicylic acid improves resistance of aphid-susceptible wheat to the grain aphid, Sitobion avenae (F.) (Hemiptera: Aphididae)

Salicylic acid (SA), a phytohormone, has been considered to be a key regulator mediating plant defence against pathogens. It is still vague how SA activates plant defence against herbivores such as chewing and sucking pests. Here, we used an aphid-susceptible wheat variety to investigate Sitobion avenae response to SA-induced wheat plants, and the effects of exogenous SA on some defence enzymes and phenolics in the plant immune system. In SA-treated wheat seedlings, intrinsic rate of natural increase (rm), fecundity and apterous rate of S. avenae were 0.25, 31.4 nymphs/female and 64.4%, respectively, and significantly lower than that in the controls (P < 0.05). Moreover, the increased activities of phenylalanine-ammonia-lyase, polyphenol oxidase (PPO) and peroxidase in the SA-induced seedlings obviously depended on the sampling time, whereas activities of catalase and 4-coumarate:CoA ligase were suppressed significantly at 24, 48 and 72 h in comparison with the control. Dynamic levels of p-coumaric acid at 96 h, caffeic acid at 24 and 72 h and chlorogenic acid at 24, 48 and 96 h in wheat plants were significantly upregulated by exogenous SA application. Nevertheless, only caffeic acid content was positively correlated with PPO activity in SA-treated wheat seedlings (P = 0.031). These findings indicate that exogenous SA significantly enhanced the defence of aphid-susceptible wheat variety against aphids by regulating the plant immune system, and may prove a potential application of SA in aphid control.

Maize biochemistry in response to root herbivory was mediated by domestication, spread, and breeding

With domestication, northward spread, and breeding, maize defence against root-herbivores relied on induced defences, decreasing levels of phytohormones involved in resistance, and increasing levels of a phytohormone involved in tolerance. We addressed whether a suite of maize (Zea mays mays) phytohormones and metabolites involved in herbivore defence were mediated by three successive processes: domestication, spread to North America, and modern breeding. With those processes, and following theoretical predictions, we expected to find: a change in defence strategy from reliance on induced defences to reliance on constitutive defences; decreasing levels of phytohormones involved in herbivore resistance, and; increasing levels of a phytohormone involved in herbivore tolerance. We tested those predictions by comparing phytohormone levels in seedlings exposed to root herbivory by Diabrotica virgifera virgifera among four plant types encompassing those processes: the maize ancestor Balsas teosinte (Zea mays parviglumis), Mexican maize landraces, USA maize landraces, and USA inbred maize cultivars. With domestication, maize transitioned from reliance on induced defences in teosinte to reliance on constitutive defences in maize, as predicted. One subset of metabolites putatively involved in herbivory defence (13-oxylipins) was suppressed with domestication, as predicted, though another was enhanced (9-oxylipins), and both were variably affected by spread and breeding. A phytohormone (indole-3-acetic acid) involved in tolerance was enhanced with domestication, and with spread and breeding, as predicted. These changes are consistent with documented changes in herbivory resistance and tolerance, and occurred coincidentally with cultivation in increasingly resource-rich environments, i.e., from wild to highly enriched agricultural environments. We concluded that herbivore defence evolution in crops may be mediated by processes spanning thousands of generations, e.g., domestication and spread, as well as by processes spanning tens of generations, e.g., breeding and agricultural intensification.

Herbivory-Induced Emission of Volatile Terpenes in Chrysanthemum morifolium Functions as an Indirect Defense against Spodoptera litura Larvae by Attracting Natural Enemies

Indirect defense is an important strategy employed by sessile plants to defend against herbivorous insects by recruiting the natural enemies of herbivores mediated by herbivore-induced plant volatiles (HIPVs). We aimed to determine whether indirect defense occurs in Compositae with Chrysanthemum morifolium as the model and elucidate the mechanisms underlying the biosynthesis of HIPVs. Using two-choice olfactometer bioassays, we showed that C. morifolium plants following infestation by larvae of the tobacco cutworm (Spodoptera litura, TCW) were significantly more attractive to two natural enemies of TCW larvae than control plants, indicating that indirect defense is an active defense strategy of C. morifolium. The chemical cue responsible for indirect defense in C. morifolium was identified as a complex blend of volatiles predominated by sesquiterpenes and monoterpenes. A total of 11 candidate terpene synthase (TPS) genes were identified by comparing the transcriptomes of healthy and TCW-infested plants. Gene expression analysis confirmed that up-regulated CmjTPS genes are consistent with the elevated emission of terpenes after herbivory treatment. Our study showed that the herbivore-induced emission of JA-dependent volatile terpenes attracted both predatory and parasitic enemies of herbivores. Generally, our findings indicate that indirect defense might be an important defense mechanism against insects in C. morifolium.

Application of Plant Defense Elicitors Fails to Enhance Herbivore Resistance or Mitigate Phytoplasma Infection in Cranberries

Synthetic elicitors of the salicylic acid (SA) and jasmonic acid (JA) plant defense pathways can be used to increase crop protection against herbivores and pathogens. In this study, we tested the hypothesis that elicitors of plant defenses interact with pathogen infection to influence crop resistance against vector and nonvector herbivores. To do so, we employed a trophic system comprising of cranberries (Vaccinium macrocarpon), the phytoplasma that causes false blossom disease, and two herbivores-the blunt-nosed leafhopper (Limotettix vaccinii), the vector of false blossom disease, and the nonvector gypsy moth (Lymantria dispar). We tested four commercial elicitors, including three that activate mainly SA-related plant defenses (Actigard, LifeGard, and Regalia) and one activator of JA-related defenses (Blush). A greenhouse experiment in which phytoplasma-infected and uninfected plants received repeated exposure to elicitors revealed that both phytoplasma infection and elicitor treatment individually improved L. vaccinii and L. dispar mass compared to uninfected, untreated controls; however, SA-based elicitor treatments reduced L. vaccinii mass on infected plants. Regalia also improved L. vaccinii survival. Phytoplasma infection reduced plant size and mass, increased levels of nitrogen (N) and SA, and lowered carbon/nitrogen (C/N) ratios compared to uninfected plants, irrespective of elicitor treatment. Although none of our elicitor treatments influenced transcript levels of a phytoplasma-specific marker gene, all of them increased N and reduced C/N levels; the three SA activators also reduced JA levels. Taken together, our findings reveal positive effects of both phytoplasma infection and elicitor treatment on the performance of L. vaccinii and L. dispar in cranberries, likely via enhancement of plant nutrition and changes in phytohormone profiles, specifically increases in SA levels and corresponding decreases in levels of JA. Thus, we found no evidence that the tested elicitors of plant defenses increase resistance to insect herbivores or reduce disease incidence in cranberries.

Identification and evolution analysis of the JAZ gene family in maize

Background

Jasmonates (JAs) are important for plants to coordinate growth, reproduction, and defense responses. In JA signaling, jasmonate ZIM-domain (JAZ) proteins serve as master regulators at the initial stage of herbivores attacks. Although discovered in many plant species, little in-depth characterization of JAZ gene expression has been reported in the agronomically important crop, maize (Zea mays L.).

Results

In this study 16 JAZ genes from the maize genome were identified and classified. Phylogenetic analyses were performed from maize, rice, sorghum, Brachypodium, and Arabidopsis using deduced protein sequences, total six clades were proposed and conservation was observed in each group, such as similar gene exon/intron structures. Synteny analysis across four monocots indicated these JAZ gene families had a common ancestor, and duplication events in maize genome may drive the expansion of JAZ gene family, including genome-wide duplication (GWD), transposon, and/or tandem duplication. Strong purifying selection acted on all JAZ genes except those in group 4, which were under neutral selection. Further, we cloned three paralogous JAZ gene pairs from two maize inbreds differing in JA levels and insect resistance, and gene polymorphisms were observed between two inbreds.

Conclusions

Here we analyzed the composition and evolution of JAZ genes in maize with three other monocot plants. Extensive phylogenetic and synteny analysis revealed the expansion and selection fate of maize JAZ. This is the first study comparing the difference between two inbreds, and we propose genotype-specific JAZ gene expression might be present in maize plants. Since genetic redundancy in JAZ gene family hampers our understanding of their role in response to specific elicitors, we hope this research could be pertinent to elucidating the defensive responses in plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07522-4.

Ethylene response factors 15 and 16 trigger jasmonate biosynthesis in tomato during herbivore resistance

Jasmonates (JAs) are phytohormones with crucial roles in plant defense. Plants accumulate JAs in response to wounding or herbivore attack, but how JA biosynthesis is triggered remains poorly understood. Here we show that herbivory by cotton bollworm (Helicoverpa armigera) induced both ethylene (ET) and JA production in tomato (Solanum lycopersicum) leaves. Using RNA-seq, ET mutants, and inhibitors of ET signaling, we identified ET-induced ETHYLENE RESPONSE FACTOR 15 (ERF15) and ERF16 as critical regulators of JA biosynthesis in tomato plants. Transcripts of ERF15 and ERF16 were markedly upregulated and peaked at 60 and 15 min, respectively, after simulated herbivore attack. While mutation in ERF16 resulted in the attenuated expression of JA biosynthetic genes and decreased JA accumulation 15 min after the simulated herbivory treatment, these changes were not observed in erf15 mutants until 60 min after treatment. Electrophoretic mobility shift assays and dual-luciferase assays demonstrated that both ERFs15 and 16 are transcriptional activators of LIPOXYGENASE D, ALLENE OXIDE CYCLASE, and 12-OXO-PHYTODIENOIC ACID REDUCTASE 3, key genes in JA biosynthesis. Furthermore, JA-activated MYC2 and ERF16 also function as the transcriptional activators of ERF16, contributing to dramatic increases in ERF16 expression. Taken together, our results demonstrated that ET signaling is involved in the rapid induction of the JA burst. ET-induced ERF15 and ERF16 function as powerful transcriptional activators that trigger the JA burst in response to herbivore attack.

Glyphosate-Modulated Biosynthesis Driving Plant Defense and Species Interactions

Glyphosate has become the best-selling herbicide used in agriculture, horticulture, silviculture, and urban environments. It disrupts the shikimate metabolic pathway and thereby blocks the production of aromatic amino acids, which are the basis for several plant metabolites. Glyphosate residues are reported in soils from diverse environments, but the effects on plant physiology and consequences for species interactions are largely unknown. Here, we emphasize the complexity of these physiological processes, and argue that glyphosate residues modulate biosynthetic pathways, individually or interactively, which may affect interactions between plants and heterotrophic organisms. In this way, glyphosate residues can substantially interfere with plant resistance and the attraction of beneficial insects, both of which are essential elements in integrated pest management and healthy ecosystems.

Potential Plant-Plant Communication Induced by Infochemical Methyl Jasmonate in Sorghum (Sorghum bicolor)

Despite the fact that they are sessile organisms, plants actively move their organs and also use these movements to manipulate the surrounding biotic and abiotic environments. Plants maintain communication with neighboring plants, herbivores, and predators through the emission of diverse chemical compounds by their shoots and roots. These infochemicals modify the environment occupied by plants. Moreover, some infochemicals may induce morphophysiological changes of neighboring plants. We have used methyl-jasmonate (MeJa), a plant natural infochemical, to trigger communication between emitters and receivers Sorghum bicolor plants. The split roots of two plants were allocated to three different pots, with the middle pot containing the roots of both plants. We scored low stomatal conductance (g_S) and low CO₂ net assimilation (A) using the plants that had contact with the infochemical for the first time. During the second contact, these parameters showed no significant differences, indicating a memory effect. We also observed that the plants that had direct leaf contact with MeJa transmitted sensory information through their roots to neighboring plants. This resulted in higher maximum fluorescence (F_M) and structural changes in root anatomy. In conclusion, MeJa emerges as possible trigger for communication between neighboring sorghum plants, in response to the environmental challenges.

Seven Questions on the Chemical Ecology and Neurogenetics of Resource-Mediated Speciation

Adaptation to different environments can result in reproductive isolation between populations and the formation of new species. Food resources are among the most important environmental factors shaping local adaptation. The chemosensory system, the most ubiquitous sensory channel in the animal kingdom, not only detects food resources and their chemical composition, but also mediates sexual communication and reproductive isolation in many taxa. Chemosensory divergence may thus play a crucial role in resource-mediated adaptation and speciation. Understanding how the chemosensory system can facilitate resource-mediated ecological speciation requires integrating mechanistic studies of the chemosensory system with ecological studies, to link the genetics and physiology of chemosensory properties to divergent adaptation. In this review, we use examples of insect research to present seven key questions that can be used to understand how the chemosensory system can facilitate resource-mediated ecological speciation in consumer populations.

Oxylipins are implicated as communication signals in tomato-root-knot nematode (Meloidogyne javanica) interaction

Throughout infection, plant-parasitic nematodes activate a complex host defense response that will regulate their development and aggressiveness. Oxylipins-lipophilic signaling molecules-are part of this complex, performing a fundamental role in regulating plant development and immunity. At the same time, the sedentary root-knot nematode Meloidogyne spp. secretes numerous effectors that play key roles during invasion and migration, supporting construction and maintenance of nematodes' feeding sites. Herein, comprehensive oxylipin profiling of tomato roots, performed using LC-MS/MS, indicated strong and early responses of many oxylipins following root-knot nematode infection. To identify genes that might respond to the lipidomic defense pathway mediated through oxylipins, RNA-Seq was performed by exposing Meloidogyne javanica second-stage juveniles to tomato protoplasts and the oxylipin 9-HOT, one of the early-induced oxylipins in tomato roots upon nematode infection. A total of 7512 differentially expressed genes were identified. To target putative effectors, we sought differentially expressed genes carrying a predicted secretion signal peptide. Among these, several were homologous with known effectors in other nematode species; other unknown, potentially secreted proteins may have a role as root-knot nematode effectors that are induced by plant lipid signals. These include effectors associated with distortion of the plant immune response or manipulating signal transduction mediated by lipid signals. Other effectors are implicated in cell wall degradation or ROS detoxification at the plant-nematode interface. Being an integral part of the plant's defense response, oxylipins might be placed as important signaling molecules underlying nematode parasitism.

Cytokinin response induces immunity and fungal pathogen resistance, and modulates trafficking of the PRR LeEIX2 in tomato

Plant immunity is often defined by the immunity hormones: salicylic acid (SA), jasmonic acid (JA), and ethylene (ET). These hormones are well known for differentially regulating defence responses against pathogens. In recent years, the involvement of other plant growth hormones such as auxin, gibberellic acid, abscisic acid, and cytokinins (CKs) in biotic stresses has been recognized. Previous reports have indicated that endogenous and exogenous CK treatment can result in pathogen resistance. We show here that CK induces systemic immunity in tomato (Solanum lycopersicum), modulating cellular trafficking of the pattern recognition receptor (PRR) LeEIX2, which mediates immune responses to Xyn11 family xylanases, and promoting resistance to Botrytis cinerea and Oidium neolycopersici in an SA- and ET-dependent mechanism. CK perception within the host underlies its protective effect. Our results support the notion that CK promotes pathogen resistance by inducing immunity in the host.

Envisioning the immune interactome in Arabidopsis

During plant-pathogen interaction, immune targets were regulated by protein-protein interaction events such as ligand-receptor/co-receptor, kinase-substrate, protein sequestration, activation or repression via post-translational modification and homo/oligo/hetro-dimerisation of proteins. A judicious use of molecular machinery requires coordinated protein interaction among defence components. Immune signalling in Arabidopsis can be broadly represented in successive or simultaneous steps; pathogen recognition at cell surface, Ca2+ and reactive oxygen species signalling, MAPK signalling, post-translational modification, transcriptional regulation and phyto-hormone signalling. Proteome wide interaction studies have shown the existence of interaction hubs associated with physiological function. So far, a number of protein interaction events regulating immune targets have been identified, but their understanding in an interactome view is lacking. We focussed specifically on the integration of protein interaction signalling in context to plant-pathogenesis and identified the key targets. The present review focuses towards a comprehensive view of the plant immune interactome including signal perception, progression, integration and physiological response during plant pathogen interaction.

Larval Performance of a Major Forest Pest on Novel Hosts and the Effect of Stressors

Novel hosts lacking a coevolutionary history with herbivores can often support improved larval performance over historic hosts; e.g., emerald ash borer [Agrilus planipennis (Fairmaire) Coleoptera: Buprestidae] on North American ash (Fraxinus spp.) trees. Whether trees are novel or ancestral, stress on plants increases emerald ash borer preference and performance. White fringetree [Chionanthus virginicus (L.) Lamiales: Oleaceae] and olive [Olea europaea (L.) Lamiales: Oleaceae] are closely related non-ash hosts that support development of emerald ash borer to adulthood, but their relative suitability as hosts and the impact of plant stress on larval success has not been well studied. In a series of experiments, survival and growth of emerald ash borer larvae on these novel hosts were examined along with the impact of stress. In the first experiment, larvae grew more slowly in cut stems of olive than in green ash [Fraxinus pennsylvanica (Marshall) Lamiales: Oleaceae] and several adults successfully emerged from larger olive stems. In two experiments on young potted olive with photosynthesizing bark, larvae died within a week, but mechanical girdling increased the rate of gallery establishment. The final two experiments on field-grown fringetrees found increased larval survivorship and growth in previously emerald ash borer attacked and mechanically girdled plants than in healthy stems or stems treated with the defense hormone, methyl jasmonate. Our results demonstrate that these non-ash hosts are less suitable for emerald ash borer than preferred ash hosts, but previous emerald ash borer attack or girdling led to better survival and growth demonstrating the importance of stress for larval success. In potted olive, high mortality could be due to higher loads of toxic compounds or the presence of chlorophyllous tissue.

Root colonization by endophytic insect-pathogenic fungi

Several ascomycetous insect-pathogenic fungi, including species in the genera Beauveria and Metarhizium, are plant root symbionts/endophytes and are termed as endophytic insect-pathogenic fungi (EIPF). The endophytic capability and insect pathogenicity of Metarhizium are coupled to provide an active method of insect-derived nitrogen transfer to plant hosts via fungal mycelia. In exchange for the insect-derived nitrogen, the plant provides photosynthate to the fungus. This symbiotic interaction offers other benefits to the plant-EIPF can improve plant growth, they are antagonistic to plant pathogens and herbivores and can enhance the plant tolerance to abiotic stresses. The mechanisms and underlying biochemical and genetic features of insect pathogenesis are generally well-established. However, there is a paucity of information regarding the underlying mechanisms in this plant-symbiotic association. Here we review five aspects of EIPF interactions with host plant roots: (i) rhizosphere colonization, (ii) signalling factors from the plant and EIPF, (iii) modulation of plant defence responses, (iv) nutrient exchange and (v) tripartite interactions with insects and other micro-organisms. The elucidation of these interactions is fundamental to understanding this symbiotic association for effective application of EIPF in an agricultural setting.

Plant Defense by Latex: Ecological Genetics of Inducibility in the Milkweeds and a General Review of Mechanisms, Evolution, and Implications for Agriculture

Latex occurs in 10% of plant families, has evolved independently many times, and is the most effective defense of milkweeds against its chewing herbivores. Here we report on new experiments on the heritability and inducibility of latex in several milkweed species. In addition, we review what is known about the genetic and environmental determinants of latex exudation, hormonal regulation, evolution within and among species, and the role and frequency of latex in agricultural crops. We first evaluated genotype-by-environment interactions using ~20 full-sibling genetic families in each of seven Asclepias species treated as controls or attacked by monarch butterfly caterpillars. All species showed substantial genetic variation for latex exudation and six of seven species responded to monarch herbivory (two species increased latex, two species decreased, and two showed variation among genetic families). Exogenous application of jasmonic acid (JA) to three species induced a consistent increase in latex (including species which showed a decline following caterpillar herbivory). We next evaluated three hypotheses for what determines genetic variation for induced latex in A. syriaca: 1) a trade-off with constitutive investment, 2) differential endogenous JA induction, or 3) variation in responsiveness to JA. We only found support for the second hypothesis: genetic families with a stronger JA-burst showed the greatest latex exudation following herbivory. We conclude that most species exhibit a genetic and inducible basis for latex, although genetic variation in inducibility is not pervasive. Finally, we summarized studies across 22 species of Asclepias and found that neither a species' latitude nor its phylogenetic position predicted latex inducibility. Nonetheless, a negative association between constitutive and induced latex across species indicates a macroevolutionary trade-off in allocation to this defense. Our review indicates that jasmonic acid is a key regulator of latex exudation, laticifer morphology, and defensive metabolites within latex. Biotic and abiotic factors strongly modulate latex expression. A survey of latex in food crops revealed that latex and analogous exudates (gums, resins, mucilage) are more common than expected based on their distribution across all plants. In conclusion, despite its widespread occurrence, the literature on latex is currently dominated by rubber trees and milkweeds, and we look forward to the broadening of ecological, agricultural, and mechanistic research into other systems.

RNA-seq of eight different poplar clones reveals conserved up-regulation of gene expression in response to insect herbivory

BACKGROUND

Herbivorous insects can have a profound impact on plant growth performance. In some years, canopy damage in poplar plantations exceeds 50% of the total leaf surface, thereby possibly compromising carbon fixation and biomass yield. To assess the transcriptional response of elite poplar clones to insect feeding and to test whether this response varies between different genotypes, we performed an RNA-sequencing experiment. We deeply sequenced the transcriptomes of eight elite clones belonging to three poplar species (Populus trichocarpa, P. nigra and P. maximowiczii), under Phratora vitellinae feeding and control conditions. This allowed us to precisely quantify transcript levels of about 24,000 expressed genes.

RESULTS

Our data reveal a striking overall up-regulation of gene expression under insect attack in all eight poplar clones studied. The up-regulated genes were markedly enriched for the biological process 'regulation of transcription' indicating a highly concerted restructuring of the transcriptome. A search for potential cis-regulatory elements (CREs) that may be involved in this process identified the G-box (CACGTG) as the most significant motif in the promoters of the induced genes. In line with the role of the G-box in jasmonate (JA)-mediated activation of gene expression by MYC2, several genes involved in JA biosynthesis and signaling were up-regulated in our dataset. A co-expression network analysis additionally highlighted WRKY transcription factors. Within the most prominent expression module, WRKYs were strongly overrepresented and occupied several network hubs. Finally, the insect-induced genes comprised several protein families known to be involved in plant defenses, e.g. cytochrome P450s, chitinases and protease inhibitors.

CONCLUSIONS

Our data represent a comprehensive characterization of the transcriptional response of selected elite poplar clones to insect herbivory. Our results suggest that the concerted up-regulation of gene expression is controlled by JA signaling and WRKY transcription factors, and activates several defense mechanisms. Our data highlight potential targets of selection and may thus contribute to breeding insect-resistant poplar clones.

OsbZIP81, A Homologue of Arabidopsis VIP1, May Positively Regulate JA Levels by Directly Targetting the Genes in JA Signaling and Metabolism Pathway in Rice

Rice (Oryza sativa L.) is one of the most important food crops in the world. In plants, jasmonic acid (JA) plays essential roles in response to biotic and abiotic stresses. As one of the largest transcription factors (TFs), basic region/leucine zipper motif (bZIP) TFs play pivotal roles through the whole life of plant growth. However, the relationship between JA and bZIP TFs were rarely reported, especially in rice. In this study, we found two rice homologues of Arabidopsis VIP1 (VirE2-interacting protein 1), OsbZIP81, and OsbZIP84. OsbZIP81 has at least two alternative transcripts, OsbZIP81.1 and OsbZIP81.2. OsbZIP81.1 and OsbZIP84 are typical bZIP TFs, while OsbZIP81.2 is not. OsbZIP81.1 can directly bind OsPIOX and activate its expression. In OsbZIP81.1 overexpression transgenic rice plant, JA (Jasmonic Acid) and SA (Salicylic acid) were up-regulated, while ABA (Abscisic acid) was down-regulated. Moreover, Agrobacterium, Methyl Jasmonic Acid (MeJA), and PEG6000 can largely induce OsbZIP81. Based on ChIP-Seq and Random DNA Binding Selection Assay (RDSA), we identified a novel cis-element OVRE (Oryza VIP1 response element). Combining ChIP-Seq and RNA-Seq, we obtained 1332 targeted genes that were categorized in biotic and abiotic responses, including α-linolenic acid metabolism and fatty acid degradation. Together, these results suggest that OsbZIP81 may positively regulate JA levels by directly targeting the genes in JA signaling and metabolism pathway in rice.

Testing the Distraction Hypothesis: Do extrafloral nectaries reduce ant-pollinator conflict?

Ant guards protect plants from herbivores, but can also hinder pollination by damaging reproductive structures and/or repelling pollinators. Natural selection should favour the evolution of plant traits that deter ants from visiting flowers during anthesis, without waiving their defensive services. The Distraction Hypothesis posits that rewarding ants with extrafloral nectar could reduce their visitation of flowers, reducing ant-pollinator conflict while retaining protection of other structures.We characterised the proportion of flowers occupied by ants and the number of ants per flower in a Mexican ant-plant, Turnera velutina. We clogged extrafloral nectaries on field plants and observed the effects on patrolling ants, pollinators and ants inside flowers, and quantified the effects on plant fitness. Based on the Distraction Hypothesis, we predicted that preventing extrafloral nectar secretion should result in fewer ants active at extrafloral nectaries, more ants inside flowers and a higher proportion of flowers occupied by ants, leading to ant-pollinator conflict, with reduced pollinator visitation and reduced plant fitness.Overall ant activity inside flowers was low. Preventing extrafloral nectar secretion through clogging reduced the number of ants patrolling extrafloral nectaries, significantly increased the proportion of flowers occupied by ants from 6.1% to 9.7%, and reduced plant reproductive output through a 12% increase in the probability of fruit abortion. No change in the numbers of ants or pollinators inside flowers was observed. This is the first support for the Distraction Hypothesis obtained under field conditions, showing ecological and plant fitness benefits of the distracting function of extrafloral nectar during anthesis. Synthesis. Our study provides the first field experimental support for the Distraction Hypothesis, suggesting that extrafloral nectaries located close to flowers may bribe ants away from reproductive structures during the crucial pollination period, reducing the probability of ant occupation of flowers, reducing ant-pollinator conflict and increasing plant reproductive success.

Sodium chloride primes JA-independent defense against Spodoptera litura (Fabricius) larvae in Arabidopsis thaliana

Priming for better defense performance is an important strategy in acclimation to the ever-changing environment. In the present study, defense priming induced by sodium chloride at the seedling stage significantly increased the expression of defense gene VSP2, the content of total glucosinolates and the level of the reactive oxygen species in mature Arabidopsis thaliana plants after transferred into the stress-free environment. The previously primed plants could effectively resist the feeding of Spodoptera litura (Fabricius) larvae. Salt-priming enhanced defense of Arabidopsis plants in the absence of either MYC2 or AOS, which encodes a critical transcription factor in JA-signaling and an important enzyme in JA biosynthesis, respectively. Our results supported the JA-independent defense primed by sodium chloride, as well as the elevated ROS and glucosinolate level in primed plants. In addition, the feasibility of using mild salt-priming to improve crop performance in field was proposed.

The moss jasmonate ZIM-domain protein PnJAZ1 confers salinity tolerance via crosstalk with the abscisic acid signalling pathway

Abscisic acid (ABA) and jasmonates (JAs) are the primary plant hormones involved in mediating salt tolerance. In addition, these two plant hormones exert a synergistic effect to inhibit seed germination. However, the molecular mechanism of the interaction between ABA signalling and JA signalling is still not well documented. Here, a moss jasmonate ZIM-domain gene (PnJAZ1), which encodes a nucleus-localized protein with conserved ZIM and Jas domains, was cloned from Pohlia nutans. PnJAZ1 expression was rapidly induced by various abiotic stresses. The PnJAZ1 protein physically interacted with MYC2 and was degraded by exogenous 12-oxo-phytodienoic acid (OPDA) treatment, implying that the JAZ protein-mediated signalling pathway is conserved in plants. Transgenic Arabidopsis and Physcomitrella plants overexpressing PnJAZ1 showed increased tolerance to salt stress and decreased ABA sensitivity during seed germination and early development. The overexpression of PnJAZ1 inhibited the expression of ABA pathway genes related to seed germination and seedling growth. Moreover, the transgenic Arabidopsis lines exhibited enhanced tolerance to auxin (IAA) and glucose, mimicking the phenotypes of abi4 or abi5 mutants. These results suggest that PnJAZ1 acts as a repressor, mediates JA-ABA synergistic crosstalk and enhances plant growth under salt stress.

Endophyte Infection and Methyl Jasmonate Treatment Increased the Resistance of Achnatherum sibiricum to Insect Herbivores Independently

Alkaloids are usually thought to be responsible for protecting endophyte-infected (EI) grasses from their herbivores. For EI grasses that produce few alkaloids, can endophyte infection enhance their resistance to herbivores? Related studies are limited. In the Inner Mongolian steppe, Achnatherum sibiricum is highly infected by Epichloë endophytes, but produces few alkaloids. Locusts are the common insect herbivores of grasses. In this study, A. sibiricum was used as plant material. Methyl jasmonate (MJ, when applied exogenously, can induce responses similar to herbivore damage) treatment was performed. The effects of endophyte infection and MJ treatment on the resistance of A. sibiricum to Locusta migratoria were studied. We found that locusts preferred EF (endophyte-free) plants to EI plants in both choice and no-choice feeding experiments. Endophyte infection enhanced the resistance of A. sibiricum to locusts. Endophyte infection decreased soluble sugar concentrations, while it increased the total phenolic content and phenylalanine ammonia lyase (PAL) activity, which may contribute to the resistance of A. sibiricum to locusts. There was an interaction effect between MJ treatment and endophyte infection on the growth of the host. MJ treatment was a negative regulator of the plant growth-promoting effects of endophyte infection. There was no interaction effect between MJ treatment and endophyte infection on the defense characteristics of the host. In groups not exposed to locusts, MJ treatment and endophyte infection had a similar effect in decreasing the soluble sugar content, while increasing the total phenolic content and the PAL activity. In groups exposed to locusts, the effect of MJ treatment on the above characteristics disappeared, while the effect of endophyte infection became more obvious. All of these results suggest that even for endophytes producing few alkaloids, they could still increase the resistance of native grasses to insect herbivores. Furthermore, endophyte infection might mediate the defense responses of the host, independent of jasmonic acid (JA) pathways.

Type VI glandular trichome density and their derived volatiles are differently induced by jasmonic acid in developing and fully developed tomato leaves: Implications for thrips resistance

Variation in the induction of plant defenses along the plant canopy can determine distribution and colonization of arthropod herbivores within the plant. In tomato, type VI glandular trichomes, which are epidermal defensive structures, and their derived volatiles are induced by the phytohormone jasmonic acid (JA). How JA-mediated induction of these trichome-associated chemical defenses depends on the leaf developmental stage and correlates with resistance against herbivory is unknown. We showed that application of JA reduced thrips-associated damage, however the amplitude of this response was reduced in the fully developed leaves compared to those still developing. Although JA increased type-VI trichome densities in all leaf developmental stages, as well as JA-inducible defensive proteins, these increases were stronger in developing leaves. Remarkably, the concentration of trichome-derived volatiles was induced by JA to a larger degree in developing leaves than in fully developed leaves. In fully developed leaves, the increase in trichome-derived volatiles was explained by an enhanced production per trichome, while in developing leaves this was mainly caused by increases in type-VI trichome densities. Together, we showed that JA-mediated induction of trichome density and chemistry depends on leaf development stage, and it might explain the degree of thrips-associated leaf damage in tomato.

Consortium of five fungal isolates conditioning root growth and arbuscular mycorrhiza in soybean, corn, and sugarcane

Plant growth and arbuscular mycorrhizal colonization were studied in sugarcane, corn and soybean by applying five plant growth promoting fungi: Beauveria bassiana, Metarhizium anisopliae, Pochonia chlamydosporia, Purpureocillium lilacinum, and Trichoderma asperella. Sugarcane, corn and soybean were grown in pots under two treatments: (1) inoculation with the fungal consortium and (2) control without inoculation. In the inoculated treatment, fungal spore suspension were applied to the seeds and shoots were sprayed every 28 days. Means were analyzed by analysis of variance and Tukey's test at 5% probability level. The experiment was arranged in a completely randomized design, with six replications. Fungi consortium mediate root growth in soybean and corn, and arbuscular mycorrhizal colonization in soybean and sugarcane. These findings are probably caused by the fungi producing phytohormones and inducing the plants to synthesize phytohormones: auxins for root growth; and jasmonic, abscisic, and salicylic acids with a role in the regulation of mycorrhizal colonization. These effects are important when seeking conservation strategies in agriculture and livestock production, since Fungi consortium can better mediate soil resource acquisition, promoting greater absorption of nutrients and water.

Searching for best lower dimensional visualization angles for high dimensional RNA-Seq data

The accumulation of RNA sequencing (RNA-Seq) gene expression data in recent years has resulted in large and complex data sets of high dimensions. Exploratory analysis, including data mining and visualization, reveals hidden patterns and potential outliers in such data, but is often challenged by the high dimensional nature of the data. The scatterplot matrix is a commonly used tool for visualizing multivariate data, and allows us to view multiple bivariate relationships simultaneously. However, the scatterplot matrix becomes less effective for high dimensional data because the number of bivariate displays increases quadratically with data dimensionality. In this study, we introduce a selection criterion for each bivariate scatterplot and design/implement an algorithm that automatically scan and rank all possible scatterplots, with the goal of identifying the plots in which separation between two pre-defined groups is maximized. By applying our method to a multi-experiment Arabidopsis RNA-Seq data set, we were able to successfully pinpoint the visualization angles where genes from two biological pathways are the most separated, as well as identify potential outliers.