Interplant signalling through hyphal networks

The evolution of signaling and monitoring in plant-fungal networks

Experiments have shown that when one plant is attacked by a pathogen or herbivore, this can lead to other plants connected to the same mycorrhizal network up-regulating their defense mechanisms. It has been hypothesized that this represents signaling, with attacked plants producing a signal to warn other plants of impending harm. We examined the evolutionary plausibility of this and other hypotheses theoretically. We found that the evolution of plant signaling about an attack requires restrictive conditions, and so will rarely be evolutionarily stable. The problem is that signaling about an attack provides a benefit to competing neighbors, even if they are kin, and so reduces the relative fitness of signaling plants. Indeed, selection is often more likely to push plant behavior in the opposite direction-with plants signaling dishonestly about an attack that has not occurred, or suppressing a cue that they have been attacked. Instead, we show that there are two viable alternatives that could explain the empirical data: 1) the process of being attacked leads to a cue (information about the attack) which is too costly for the attacked plant to fully suppress; 2) mycorrhizal fungi monitor their host plants, detect when they are attacked, and then the fungi signal this information to warn other plants in their network. Our results suggest the empirical work that would be required to distinguish between these possibilities.

Electrical signaling in fungi: past and present challenges

Electrical signaling is a fundamental mechanism for integrating environmental stimuli and coordinating responses in living organisms. While extensively studied in animals and plants, the role of electrical signaling in fungi remains a largely underexplored field. Early studies suggested that filamentous fungi generate action potential-like signals and electrical currents at hyphal tips, yet their function in intracellular communication remained unclear. Renewed interest in fungal electrical activity has fueled developments such as the hypothesis that mycorrhizal networks facilitate electrical communication between plants and the emerging field of fungal-based electronic materials. Given their continuous plasma membrane, specialized septal pores, and insulating cell wall structures, filamentous fungi possess architectural features that could support electrical signaling over long distances. However, studying electrical phenomena in fungal networks presents unique challenges due to the microscopic dimensions of hyphae, the structural complexity of highly modular mycelial networks, and the limitations of traditional electrophysiological methods. This review synthesizes current evidence for electrical signaling in filamentous fungi, evaluates methodological approaches, and highlights experimental challenges. By addressing these challenges and identifying best practices, we aim to advance research in this field and provide a foundation for future studies exploring the role of electrical signaling in fungal biology.

The biology and chemistry of a mutualism between a soil bacterium and a mycorrhizal fungus

Arbuscular mycorrhizal (AM) fungi (e.g., Rhizophagus species) recruit specific bacterial species in their hyphosphere. However, the chemical interplay and the mutual benefit of this intricate partnership have not been investigated yet, especially as it involves bacteria known as strong producers of antifungal compounds such as Bacillus velezensis. Here, we show that the soil-dwelling B. velezensis migrates along the hyphal network of the AM fungus R. irregularis, forming biofilms and inducing cytoplasmic flow in the AM fungus that contributes to host plant root colonization by the bacterium. During hyphosphere colonization, R. irregularis modulates the biosynthesis of specialized metabolites in B. velezensis to ensure stable coexistence and as a mechanism to ward off mycoparasitic fungi and bacteria. These mutual benefits are extended into a tripartite context via the provision of enhanced protection to the host plant through the induction of systemic resistance.

Plant Immunity Modulation in Arbuscular Mycorrhizal Symbiosis and Its Impact on Pathogens and Pests

Arbuscular mycorrhizal (AM) symbiosis is the oldest and most widespread mutualistic association on Earth and involves plants and soil fungi belonging to Glomeromycotina. A complex molecular, cellular, and genetic developmental program enables partner recognition, fungal accommodation in plant tissues, and activation of symbiotic functions such as transfer of phosphorus in exchange for carbohydrates and lipids. AM fungi, as ancient obligate biotrophs, have evolved strategies to circumvent plant defense responses to guarantee an intimate and long-lasting mutualism. They are among those root-associated microorganisms able to boost plants' ability to cope with biotic stresses leading to mycorrhiza-induced resistance (MIR), which can be effective across diverse hosts and against different attackers. Here, we examine the molecular mechanisms underlying the modulation of plant immunity during colonization by AM fungi and at the onset and display of MIR against belowground and aboveground pests and pathogens. Understanding the MIR efficiency spectrum and its regulation is of great importance to optimizing the biotechnological application of these beneficial microbes for sustainable crop protection.

Electrical integrity and week-long oscillation in fungal mycelia

The electrical potential of the mycelia of a cord-forming wood decay fungus, Pholiota brunnescens, was monitored for over 100 days on a plain agar plate during the colonization onto a wood bait. Causality analyses of the electrical potential at different locations of the mycelium revealed a clear and stable causal relationship with the directional flow of the electrical potential from the hyphae at the bait location to other parts of the mycelium. However, this causality disappeared after 60 days of incubation, coinciding with the onset of slow electrical oscillation at the bait location, which occurred over one week per oscillation cycle. We speculated that the hyphae that initially colonized the bait may act as a temporary activity center, which generates electrical signals to other parts of the mycelium, thereby facilitating the colonization of the entire mycelial body to the bait. The week-long electrical oscillation represents the longest oscillation period ever recorded in fungi and warrants further investigation to elucidate its function and stability in response to environmental stimuli.

Arbuscular Mycorrhizal Fungi as Biostimulant and Biocontrol Agents: A Review

Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.

Belowground ecological interactions in dioecious plants: why do opposites attract but similar ones repel?

Dioecious plant species exhibit sexual dimorphism in various aspects, including morphology, physiology, life history, and behavior, potentially influencing sex-specific interactions. While it is generally accepted that intersexual interactions in dioecious species are less intense compared with intrasexual interactions, the mechanisms underlying belowground facilitation in intersexual combinations remain less understood. Here, we explore these mechanisms, which encompass resource complementarity, mycorrhizal fungal networks, root exudate-mediated belowground chemical communication, as well as plant-soil feedback. We address the reason for the lack of consistency in the strength of inter- and intrasexual interactions. We also propose that a comprehensive understanding of the potential positive consequences of sex-specific interactions can contribute to maintaining ecological equilibrium, conserving biodiversity, and enhancing the productivity of agroforestry.

Facilitative and competitive interactions between mycorrhizal and nonmycorrhizal plants in an extremely phosphorus-impoverished environment: role of ectomycorrhizal fungi and native oomycete pathogens in shaping species coexistence

Nonmycorrhizal cluster root-forming species enhance the phosphorus (P) acquisition of mycorrhizal neighbours in P-impoverished megadiverse systems. However, whether mycorrhizal plants facilitate the defence of nonmycorrhizal plants against soil-borne pathogens, in return and via their symbiosis, remains unknown. We characterised growth and defence-related compounds in Banksia menziesii (nonmycorrhizal) and Eucalyptus todtiana (ectomycorrhizal, ECM) seedlings grown either in monoculture or mixture in a multifactorial glasshouse experiment involving ECM fungi and native oomycete pathogens. Roots of B. menziesii had higher levels of phytohormones (salicylic and jasmonic acids, jasmonoyl-isoleucine and 12-oxo-phytodienoic acid) than E. todtiana which further activated a salicylic acid-mediated defence response in roots of B. menziesii, but only in the presence of ECM fungi. We also found that B. menziesii induced a shift in the defence strategy of E. todtiana, from defence-related secondary metabolites (phenolic and flavonoid) towards induced phytohormone response pathways. We conclude that ECM fungi play a vital role in the interactions between mycorrhizal and nonmycorrhizal plants in a severely P-impoverished environment, by introducing a competitive component within the facilitation interaction between the two plant species with contrasting nutrient-acquisition strategies. This study sheds light on the interplay between beneficial and detrimental soil microbes that shape plant-plant interaction in severely nutrient-impoverished ecosystems.

Common mycorrhizal network: the predominant socialist and capitalist responses of possible plant-plant and plant-microbe interactions for sustainable agriculture

Plants engage in a variety of interactions, including sharing nutrients through common mycorrhizal networks (CMNs), which are facilitated by arbuscular mycorrhizal fungi (AMF). These networks can promote the establishment, growth, and distribution of limited nutrients that are important for plant growth, which in turn benefits the entire network of plants. Interactions between plants and microbes in the rhizosphere are complex and can either be socialist or capitalist in nature, and the knowledge of these interactions is equally important for the progress of sustainable agricultural practice. In the socialist network, resources are distributed more evenly, providing benefits for all connected plants, such as symbiosis. For example, direct or indirect transfer of nutrients to plants, direct stimulation of growth through phytohormones, antagonism toward pathogenic microorganisms, and mitigation of stresses. For the capitalist network, AMF would be privately controlled for the profit of certain groups of plants, hence increasing competition between connected plants. Such plant interactions invading by microbes act as saprophytic and cause necrotrophy in the colonizing plants. In the first case, an excess of the nutritional resources may be donated to the receiver plants by direct transfer. In the second case, an unequal distribution of resources occurs, which certainly favor individual groups and increases competition between interactions. This largely depends on which of these responses is predominant ("socialist" or "capitalist") at the moment plants are connected. Therefore, some plant species might benefit from CMNs more than others, depending on the fungal species and plant species involved in the association. Nevertheless, benefits and disadvantages from the interactions between the connected plants are hard to distinguish in nature once most of the plants are colonized simultaneously by multiple fungal species, each with its own cost-benefits. Classifying plant-microbe interactions based on their habitat specificity, such as their presence on leaf surfaces (phyllospheric), within plant tissues (endophytic), on root surfaces (rhizospheric), or as surface-dwelling organisms (epiphytic), helps to highlight the dense and intricate connections between plants and microbes that occur both above and below ground. In these complex relationships, microbes often engage in mutualistic interactions where both parties derive mutual benefits, exemplifying the socialistic or capitalistic nature of these interactions. This review discusses the ubiquity, functioning, and management interventions of different types of plant-plant and plant-microbe interactions in CMNs, and how they promote plant growth and address environmental challenges for sustainable agriculture.

Foraging strategies of fungal mycelial networks: responses to quantity and distance of new resources

Fungal mycelial networks are essential for translocating and storing water, nutrients, and carbon in forest ecosystems. In particular, wood decay fungi form mycelial networks that connect various woody debris on the forest floor. Understanding their foraging strategies is crucial for complehending the role of mycelium in carbon and nutrient cycling in forests. Previous studies have shown that mycelial networks initiate migration from the original woody resource (inoculum) to a new woody resource (bait) if the latter is sufficiently large but not if it is small. However, the impact of energetic costs during foraging, such as the distance to the bait, has not been considered. In the present study, we conducted full-factorial experiments with two factors, bait size (4 and 8 cm3) and distance from the inoculum (1 and 15 cm). An inoculum wood block, colonized by the wood decay fungus Phanerochaete velutina, was placed in one corner of a bioassay dish (24 cm × 24 cm) filled with unsterilized soil. Once the mycelium grew onto the soil to a distance >15 cm from the inoculum, a sterilized new bait wood block (of either size) was placed on the soil at one of the two distances to be colonized by the mycelia from the inoculum. After 50 days of incubation, the baits were harvested, and their dried weight was measured to calculate the absolute weight loss during incubation. The inoculum wood blocks were retrieved and placed on a new soil dish to determine whether the mycelium would grow out onto the soil again. If no growth occurred within 8 days of additional incubation, we concluded that the mycelium had migrated from the inoculum to the bait. The results showed that mycelia in inocula coupled with baits positioned 1 cm away migrated to the baits more frequently than those with baits positioned 15 cm away. A structural equation model revealed that bait weight loss (energy gain) and hyphal coverage on the soil (foraging cost) significantly influenced mycelial migration decisions. These findings suggest that fungal mycelia may employ their own foraging strategies based on energetic benefits.

Perspectives on Computation in Plants

Plants thrive in virtually all natural and human-adapted environments and are becoming popular models for developing robotics systems because of their strategies of morphological and behavioral adaptation. Such adaptation and high plasticity offer new approaches for designing, modeling, and controlling artificial systems acting in unstructured scenarios. At the same time, the development of artifacts based on their working principles reveals how plants promote innovative approaches for preservation and management plans and opens new applications for engineering-driven plant science. Environmentally mediated growth patterns (e.g., tropisms) are clear examples of adaptive behaviors displayed through morphological phenotyping. Plants also create networks with other plants through subterranean roots-fungi symbiosis and use these networks to exchange resources or warning signals. This article discusses the functional behaviors of plants and shows the close similarities with a perceptron-like model that could act as a behavior-based control model in plants. We begin by analyzing communication rules and growth behaviors of plants; we then show how we translated plant behaviors into algorithmic solutions for bioinspired robot controllers; and finally, we discuss how those solutions can be extended to embrace original approaches to networking and robotics control architectures.

Susceptibility and plant immune control-a case of mycorrhizal strategy for plant colonization, symbiosis, and plant immune suppression

Plants and microbes (mycorrhizal fungi to be precise) have evolved together over the past millions of years into an association that is mutualist. The plants supply the fungi with photosynthates and shelter, while the fungi reciprocate by enhancing nutrient and water uptake by the plants as well as, in some cases, control of soil-borne pathogens, but this fungi-plant association is not always beneficial. We argue that mycorrhizal fungi, despite contributing to plant nutrition, equally increase plant susceptibility to pathogens and herbivorous pests' infestation. Understanding of mycorrhizal fungi strategies for suppressing plant immunity, the phytohormones involved and the signaling pathways that aid them will enable the harnessing of tripartite (consisting of three biological systems)-plant-mycorrhizal fungi-microbe interactions for promoting sustainable production of crops.

Trichoderma hamatum can act as an inter-plant communicator of foliar pathogen infections by colonizing the roots of nearby plants: A new inter-plant "wired communication"

Trichoderma is a genus of filamentous fungi widely studied and used as a biological control agent in agriculture. However, its ability to form fungal networks for inter-plant communication by means of the so-called inter-plant "wired communication" has not yet been addressed. In our study we used the model plant Arabidopsis thaliana, the fungus Trichoderma hamatum (isolated from Brassicaceae plants) and the pathogens Sclerotinia sclerotiorum and Xanthomonas campestris (necrotrophic fungus and hemibiotrophic bacteria, respectively). We performed different combinations of isolated/neighboring plants and root colonization/non-colonization by T. hamatum, as well as foliar infections with the pathogens. In this way, we were able to determine how, in the absence of T. hamatum, there is an inter-plant communication that induces systemic resistance in neighboring plants of plants infected by the pathogens. On the other hand, the plants colonized by T. hamatum roots show a greater systemic resistance against the pathogens. Regarding the role of T. hamatum as an inter-plant communicator, it is the result of an increase in foliar signaling by jasmonic acid (increased expression of LOX1 and VSP2 genes and decreased expression of ICS1 and PR-1 genes), antagonistically increasing root signaling by salicylic acid (increased expression of ICS1 and PR-1 genes and decreased expression of LOX1 and VSP2). This situation prevents root colonization by T. hamatum of the foliarly infected plant and leads to massive colonization of the neighboring plant, where jasmonic acid-mediated systemic defenses are induced.

Pros and Cons of Biochar to Soil Potentially Toxic Element Mobilization and Phytoavailability: Environmental Implications

While the potential of biochar (BC) to immobilize potentially toxic elements (PTEs) in contaminated soils has been studied and reviewed, no review has focused on the potential use of BC for enhancing the phytoremediation efficacy of PTE-contaminated soils. Consequently, the overarching purpose in this study is to critically review the effects of BC on the mobilization, phytoextraction, phytostabilization, and bioremediation of PTEs in contaminated soils. Potential mechanisms of the interactions between BC and PTEs in soils are also reviewed in detail. We discuss the promises and challenges of various approaches, including potential environmental implications, of BC application to PTE-contaminated soils. The properties of BC (e.g., surface functional groups, mineral content, ionic content, and π-electrons) govern its impact on the (im)mobilization of PTEs, which is complex and highly element-specific. This review demonstrates the contrary effects of BC on PTE mobilization and highlights possible opportunities for using BC as a mobilizing agent for enhancing phytoremediation of PTEs-contaminated soils.

Boosting Sustainable Agriculture by Arbuscular Mycorrhiza under Stress Condition: Mechanism and Future Prospective

Global agriculture is frequently subjected to stresses from increased salt content, drought, heavy metals, and other factors, which limit plant growth and production, deteriorate soil health, and constitute a severe danger to global food security. Development of environmentally acceptable mitigation techniques against stresses and restrictions on the use of chemical fertilizers in agricultural fields is essential. Therefore, eco-friendly practises must be kept to prevent the detrimental impacts of stress on agricultural regions. The advanced metabolic machinery needed to handle this issue is not now existent in plants to deal against the stresses. Research has shown that the key role and mechanisms of arbuscular mycorrhiza fungi (AMF) to enhance plant nutrient uptake, immobilisation and translocation of heavy metals, and plant growth-promoting attributes may be suitable agents for plant growth under diversed stressed condition. The successful symbiosis and the functional relationship between the plant and AMF may build the protective regulatory mechansm against the key challenge in particular stress. AMF's compatibility with hyperaccumulator plants has also been supported by studies on gene regulation and theoretical arguments. In order to address this account, the present review included reducing the impacts of biotic and abiotic stress through AMF, the mechanisms of AMF to improve the host plant's capacity to endure stress, and the strategies employed by AM fungus to support plant survival in stressful conditions.

Microbial Inoculants as Plant Biostimulants: A Review on Risk Status

Modern agriculture systems are copiously dependent on agrochemicals such as chemical fertilizers and pesticides intended to increase crop production and yield. The indiscriminate use of these chemicals not only affects the growth of plants due to the accumulation of toxic compounds, but also degrades the quality and life-supporting properties of soil. There is a dire need to develop some green approach that can resolve these issues and restore soil fertility and sustainability. The use of plant biostimulants has emerged as an environmentally friendly and acceptable method to increase crop productivity. Biostimulants contain biological substances which may be capable of increasing or stimulating plant growth in an eco-friendly manner. They are mostly biofertilizers that provide nutrients and protect plants from environmental stresses such as drought and salinity. In contrast to the protection of crop products, biostimulants not only act on the plant's vigor but also do not respond to direct actions against pests or diseases. Plant biostimulants improve nutrient mobilization and uptake, tolerance to stress, and thus crop quality when applied to plants directly or in the rhizospheric region. They foster plant growth and development by positively affecting the crop life-cycle starting from seed germination to plant maturity. Legalized application of biostimulants causes no hazardous effects on the environment and primarily provides nutrition to plants. It nurtures the growth of soil microorganisms, which leads to enhanced soil fertility and also improves plant metabolism. Additionally, it may positively influence the exogenous microbes and alter the equilibrium of the microfloral composition of the soil milieu. This review frequently cites the characterization of microbial plant biostimulants that belong to either a high-risk group or are closely related to human pathogens such as Pueudomonas, Klebsiella, Enterobacter, Acinetobacter, etc. These related pathogens cause ailments including septicemia, gastroenteritis, wound infections, inflammation in the respiratory system, meningitis, etc., of varied severity under different conditions of health status such as immunocompromized and comorbidity. Thus it may attract the related concern to review the risk status of biostimulants for their legalized applications in agriculture. This study mainly emphasizes microbial plant biostimulants and their safe application concerns.

Aboveground herbivory does not affect mycorrhiza-dependent nitrogen acquisition from soil but inhibits mycorrhizal network-mediated nitrogen interplant transfer in maize

Arbuscular mycorrhizal fungi (AMF) are considered biofertilizers for sustainable agriculture due to their ability to facilitate plant uptake of important mineral elements, such as nitrogen (N). However, plant mycorrhiza-dependent N uptake and interplant transfer may be highly context-dependent, and whether it is affected by aboveground herbivory remains largely unknown. Here, we used ¹⁵N labeling and tracking to examine the effect of aboveground insect herbivory by Spodoptera frugiperda on mycorrhiza-dependent N uptake in maize (Zea mays L.). To minimize consumption differences and ¹⁵N loss due to insect chewing, insect herbivory was simulated by mechanical wounding and oral secretion of S. frugiperda larvae. Inoculation with Rhizophagus irregularis (Rir) significantly improved maize growth, and N/P uptake. The ¹⁵N labeling experiment showed that maize plants absorbed N from soils via the extraradical mycelium of mycorrhizal fungi and from neighboring plants transferred by common mycorrhizal networks (CMNs). Simulated aboveground leaf herbivory did not affect mycorrhiza-mediated N acquisition from soil. However, CMN-mediated N transfer from neighboring plants was blocked by leaf simulated herbivory. Our findings suggest that aboveground herbivory inhibits CMN-mediated N transfer between plants but does not affect N acquisition from soil solutions via extraradical mycorrhizal mycelium.

Volatile organic compounds shape belowground plant-fungi interactions

Volatile organic compounds (VOCs), a bouquet of chemical compounds released by all life forms, play essential roles in trophic interactions. VOCs can facilitate a large number of interactions with different organisms belowground. VOCs-regulated plant-plant or plant-insect interaction both below and aboveground has been reported extensively. Nevertheless, there is little information about the role of VOCs derived from soilborne pathogenic fungi and beneficial fungi, particularly mycorrhizae, in influencing plant performance. In this review, we show how plant VOCs regulate plant-soilborne pathogenic fungi and beneficial fungi (mycorrhizae) interactions. How fungal VOCs mediate plant-soilborne pathogenic and beneficial fungi interactions are presented and the most common methods to collect and analyze belowground volatiles are evaluated. Furthermore, we suggest a promising method for future research on belowground VOCs.

The Costs and Benefits of Plant-Arbuscular Mycorrhizal Fungal Interactions

The symbiotic interaction between plants and arbuscular mycorrhizal (AM) fungi is often perceived as beneficial for both partners, though a large ecological literature highlights the context dependency of this interaction. Changes in abiotic variables, such as nutrient availability, can drive the interaction along the mutualism-parasitism continuum with variable outcomes for plant growth and fitness. However, AM fungi can benefit plants in more ways than improved phosphorus nutrition and plant growth. For example, AM fungi can promote abiotic and biotic stress tolerance even when considered parasitic from a nutrient provision perspective. Other than being obligate biotrophs, very little is known about the benefits AM fungi gain from plants. In this review, we utilize both molecular biology and ecological approaches to expand our understanding of the plant-AM fungal interaction across disciplines.

Cooperation With Arbuscular Mycorrhizal Fungi Increases Plant Nutrient Uptake and Improves Defenses Against Insects

Plants have evolved various defense mechanisms to cope with biotic and abiotic stresses. Cooperation with microorganisms, especially arbuscular mycorrhizal fungi (AMF), strengthens the defense capabilities of host plants. To explore the effect of AMF on the growth of Elymus and the defenses against locust feeding, we designed a two-compartment device to connect or cut the mycelia and roots. We used this to investigate communication cues and pathways between donor and receiver plants. We found that AMF significantly increased the nitrogen content and decreased the carbon to nitrogen (C:N) ratio of donor plants and receiver plants and the carbon content of both. After the establishment of the common mycorrhizal network (CMN) with AMF between the two chambers, inoculations of donor plants challenged by locusts caused enhancement in four defense-related enzymes, namely, lipoxygenase, polyphenol oxidase, phenylalanine ammonia lyase, and β-1,3-glucanase, in the receiver plants. The main components of volatile organic compounds emitted by receiver plants were terpenoids. The findings indicated that AMF could not only improve plant growth but also activate the defense response of plants to insect feeding. Four defense enzymes, volatile organic compounds, and carbon and nitrogen content were involved in the defense response, and the mycelial network could act as a conduit to deliver communication signals.

Cadmium transfer between maize and soybean plants via common mycorrhizal networks

More than 80% terrestrial plants establish mutualistic symbiosis with soil-borne arbuscular mycorrhizal fungi (AMF). These fungi not only significantly improve plant nutrient acquisition and stress resistance, but also mitigate heavy metal phytotoxicity, Furthermore, the extraradical mycorrhizal mycelia can form common mycorrhizal networks (CMNs) that link roots of multiple plants in a community. Here we show that the networks mediate migration of heavy metal cadmium (Cd) from maize (Zea mays L.) to soybean (Glycine max (Linn.) Merr.) plants. CMNs between maize and soybean plants were established after inoculation of maize plants with AMF Funneliformis mosseae. Application of CdCl2 in maize plants led to 64.4% increase in the shoots and 48.2% increase in the roots in Cd content in CMNs-connected soybean plants compared to the control without Cd treatment in maize. Meanwhile, although the CMNs-connected soybean plants did not directly receive Cd supply, they upregulated transcriptional levels of Cd transport-related genes HATPase and RSTK 2.13- and 5.96-fold, respectively, induced activities of POD by 44.8% in the leaves, and increased MDA by 146.2% in the roots. Furthermore, Cd addition inhibited maize growth but mycorrhizal colonization improved plant performance in presence of Cd stress. This finding demonstrates that mycorrhizal networks mediate the transfer of Cd between plants of different species, suggesting a potential to use CMNs as a conduit to transfer toxic heavy metals from main food crops to heavy metal hyperaccumulators via intercropping.

Harnessing Synergistic Biostimulatory Processes: A Plausible Approach for Enhanced Crop Growth and Resilience in Organic Farming

Simple Summary

Demand for organically grown crops has risen globally due to its healthier and safer food products. From a sustainability perspective, organic farming offers an eco-friendly cultivation system that minimizes agrochemicals and producing food with little or no environmental footprint. However, organic agriculture’s biggest drawback is the generally lower and variable yield in contrast to conventional farming. Compatible with organic farming, the selective use of biostimulants can close the apparent yield gap between organic and conventional cultivation systems. A biostimulant is defined as natural microorganisms (bacteria, fungi) or biologically active substances that are able to improve plant growth and yield through several processes. Biostimulants are derived from a range of natural resources including organic materials (composts, seaweeds), manures (earthworms, fish, insects) and extracts derived from microbes, plant, insect or animal origin. The current trend is indicative that a mixture of biostimulants is generally delivering better growth, yield and quality rather than applying biostimulant individually. When used correctly, biostimulants are known to help plants cope with stressful situations like drought, salinity, extreme temperatures and even certain diseases. More research is needed to understand the different biostimulants, key components, and also to adjust the formulations to improve their reliability in the field.

Abstract

Demand for organically grown food crops is rising substantially annually owing to their contributions to human health. However, organic farm production is still generally lower compared to conventional farming. Nutrient availability, content consistency, uptake, assimilation, and crop responses to various stresses were reported as critical yield-limiting factors in many organic farming systems. In recent years, plant biostimulants (BSs) have gained much interest from researchers and growers, and with the objective of integrating these products to enhance nutrient use efficiency (NUE), crop performance, and delivering better stress resilience in organic-related farming. This review gave an overview of direct and indirect mechanisms of microbial and non-microbial BSs in enhancing plant nutrient uptake, physiological status, productivity, resilience to various stressors, and soil-microbe-plant interactions. BSs offer a promising, innovative and sustainable strategy to supplement and replace agrochemicals in the near future. With greater mechanistic clarity, designing purposeful combinations of microbial and non-microbial BSs that would interact synergistically and deliver desired outcomes in terms of acceptable yield and high-quality products sustainably will be pivotal. Understanding these mechanisms will improve the next generation of novel and well-characterized BSs, combining microbial and non-microbial BSs strategically with specific desired synergistic bio-stimulatory action, to deliver enhanced plant growth, yield, quality, and resilience consistently in organic-related cultivation.

Long-Term Nitrogen Deposition Alters Ectomycorrhizal Community Composition and Function in a Poplar Plantation

The continuous upsurge in soil nitrogen (N) enrichment has had strong impacts on the structure and function of ecosystems. Elucidating how plant ectomycorrhizal fungi (EMF) mutualists respond to this additional N will facilitate the rapid development and implementation of more broadly applicable management and remediation strategies. For this study, we investigated the responses of EMF communities to increased N, and how other abiotic environmental factors impacted them. Consequently, we conducted an eight-year N addition experiment in a poplar plantation in coastal eastern China that included five N addition levels: 0 (N₀), 50 (N₁), 100 (N₂), 150 (N₃), and 300 (N₄) kg N ha⁻¹ yr⁻¹. We observed that excessive N inputs reduced the colonization rate and species richness of EMF, and altered its community structure and functional traits. The total carbon content of the humus layer and available phosphorus in the mineral soil were important drivers of EMF abundance, while the content of ammonium in the humus layer and mineral soil determined the variations in the EMF community structure and mycelium foraging type. Our findings indicated that long-term N addition induced soil nutrient imbalances that resulted in a severe decline in EMF abundance and loss of functional diversity in poplar plantations.

Consciousness and cognition in plants

Unlike animal behavior, behavior in plants is traditionally assumed to be completely determined either genetically or environmentally. Under this assumption, plants are usually considered to be noncognitive organisms. This view nonetheless clashes with a growing body of empirical research that shows that many sophisticated cognitive capabilities traditionally assumed to be exclusive to animals are exhibited by plants too. Yet, if plants can be considered cognitive, even in a minimal sense, can they also be considered conscious? Some authors defend that the quest for plant consciousness is worth pursuing, under the premise that sentience can play a role in facilitating plant's sophisticated behavior. The goal of this article is not to provide a positive argument for plant cognition and consciousness, but to invite a constructive, empirically informed debate about it. After reviewing the empirical literature concerning plant cognition, we introduce the reader to the emerging field of plant neurobiology. Research on plant electrical and chemical signaling can help shed light into the biological bases for plant sentience. To conclude, we shall present a series of approaches to scientifically investigate plant consciousness. In sum, we invite the reader to consider the idea that if consciousness boils down to some form of biological adaptation, we should not exclude a priori the possibility that plants have evolved their own phenomenal experience of the world. This article is categorized under: Cognitive Biology > Evolutionary Roots of Cognition Philosophy > Consciousness Neuroscience > Cognition.

Soil fungal networks moderate density-dependent survival and growth of seedlings

Pathogenic and mutualistic fungi have contrasting effects on seedling establishment, but it remains unclear whether density-dependent survival and growth are regulated by access to different types of mycorrhizal fungal networks supported by neighbouring adult trees. Here, we conducted an extensive field survey to test how mycorrhizal and pathogenic fungal colonization of arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) seedlings in a subtropical forest respond to density of neighbouring adult trees. In addition, we undertook a hyphal exclusion experiment to explicitly test the role of soil fungal networks in driving density-dependent effects on seedling growth and survival. Conspecific adult density was a strong predictor for the relative abundance of putative pathogens, which was greater in roots of AM than of ECM seedlings, while mycorrhizal fungal abundance and colonization were not consistently affected by conspecific adult density. Both ECM and AM fungal networks counteracted conspecific density-dependent mortality, but ECM fungi were more effective at weakening the negative effects of high seedling density than AM fungi. Our findings reveal a critical role of common fungal networks in mitigating negative density-dependent effects of pathogenic fungi on seedling establishment, which provides mechanistic insights into how soil fungal diversity shapes plant community structure in subtropical forests.

Friends, neighbours and enemies: an overview of the communal and social biology of plants

Plants were traditionally seen as rather passive actors in their environment, interacting with each other only in so far as they competed for the same resources. In the last 30 years, this view has been spectacularly overturned, with a wealth of evidence showing that plants actively detect and respond to their neighbours. Moreover, there is evidence that these responses depend on the identity of the neighbour, and that plants may cooperate with their kin, displaying social behaviour as complex as that observed in animals. These plant-plant interactions play a vital role in shaping natural ecosystems, and are also very important in determining agricultural productivity. However, in terms of mechanistic understanding, we have only just begun to scratch the surface, and many aspects of plant-plant interactions remain poorly understood. In this review, we aim to provide an overview of the field of plant-plant interactions, covering the communal interactions of plants with their neighbours as well as the social behaviour of plants towards their kin, and the consequences of these interactions. We particularly focus on the mechanisms that underpin neighbour detection and response, highlighting both progress and gaps in our understanding of these fascinating but previously overlooked interactions.

Soil fungal networks maintain local dominance of ectomycorrhizal trees

The mechanisms regulating community composition and local dominance of trees in species-rich forests are poorly resolved, but the importance of interactions with soil microbes is increasingly acknowledged. Here, we show that tree seedlings that interact via root-associated fungal hyphae with soils beneath neighbouring adult trees grow faster and have greater survival than seedlings that are isolated from external fungal mycelia, but these effects are observed for species possessing ectomycorrhizas (ECM) and not arbuscular mycorrhizal (AM) fungi. Moreover, survival of naturally-regenerating AM seedlings over ten years is negatively related to the density of surrounding conspecific plants, while survival of ECM tree seedlings displays positive density dependence over this interval, and AM seedling roots contain greater abundance of pathogenic fungi than roots of ECM seedlings. Our findings show that neighbourhood interactions mediated by beneficial and pathogenic soil fungi regulate plant demography and community structure in hyperdiverse forests.

Common Mycorrhizal Network Induced JA/ET Genes Expression in Healthy Potato Plants Connected to Potato Plants Infected by Phytophthora infestans

Most plants are connected belowground via common mycorrhizal networks (CMNs). In their presence, the transmission of warning signals from diseased to uninfected plants has been reported. However, current studies have all been conducted in pots making it difficult to discriminate direct from indirect contribution of hyphae to the transmission of the signals. Here, we conducted an in vitro study with potato plantlets connected by a CMN of the arbuscular mycorrhizal fungus Rhizophagus irregularis. The plantlets were grown in physically separated compartments and their connection ensured only by the CMN. The donor potato plantlets were infected by Phytophthora infestans and defense genes analyzed 24, 48 and 120 h post-infection (hpi) in the uninfected receiver potato plantlets. Twenty-four hpi by the pathogen, PAL, PR-1b, ERF3, and LOX genes were significantly upregulated, whereas no significant transcript variation was noticed 48 and 120 hpi. The exact nature of the warning signals remains unknown but was not associated to microorganisms other than the AMF or to diffusion mechanisms through the growth medium or induced by volatile compounds. The defense response appeared to be transitory and associated with the jasmonic acid or ethylene pathway. These findings demonstrate the direct involvement of hyphae in the transmission of warning signals from diseased to uninfected potato plantlets and their indubitable role in providing a route for activating defense responses in uninfected plants.

How mycorrhizal associations drive plant population and community biology

Mycorrhizal fungi provide plants with a range of benefits, including mineral nutrients and protection from stress and pathogens. Here we synthesize current information about how the presence and type of mycorrhizal association affect plant communities. We argue that mycorrhizal fungi regulate seedling establishment and species coexistence through stabilizing and equalizing mechanisms such as soil nutrient partitioning, feedback to soil antagonists, differential mycorrhizal benefits, and nutrient trade. Mycorrhizal fungi have strong effects on plant population and community biology, with mycorrhizal type-specific effects on seed dispersal, seedling establishment, and soil niche differentiation, as well as interspecific and intraspecific competition and hence plant diversity.

Vegetable Temporalities: Life cycles, maturation and death in an Amerindian ethnography

Abstract This article considers how relations with certain plants produce multiple temporalities for the Wajãpi, an Amerindian people from the Brazilian Amazon. Inspired by a non-anthropocentric anthropology or an “anthropology beyond the human,” the article is an ethnographic exploration about how the Wajãpi perceive the concrete and sensible features of certain vegetable species, and thus how they see them as subjects, in a process that produces different space-times. I also show how certain concepts are central to this same process, specifically, that of life cycle and maturation (including death), which lead to notions of co-temporality and difference between groups and individuals.

Recovery of Extra-Radical Fungal Peptides Amenable for Shotgun Protein Profiling in Arbuscular Mycorrhizae

In arbuscular mycorrhizal symbiosis, the belowground mycelium that develops into the soil, not only provides extensive pathways for nutrient fluxes, the occupation of different niches, and dispersal of propagules, but also has strong influences upon biogeochemical cycling. By providing a valuable overview of expression changes of most proteins, shotgun proteomics can help decipher key metabolic pathways involved in the functioning of fungal mycelia. In this protocol, we describe the combination of extra-radical mycelium growth systems with gel-based extraction of fungal peptides amenable for shotgun protein profiling, which allows gaining information about the extra-radical proteome.

Lotus japonicus Symbiosis Genes Impact Microbial Interactions between Symbionts and Multikingdom Commensal Communities

Studies on symbiosis genes in plants typically focus on binary interactions between roots and soilborne nitrogen-fixing rhizobia or mycorrhizal fungi in laboratory environments. We utilized wild type and symbiosis mutants of a model legume, grown in natural soil, in which bacterial, fungal, or both symbioses are impaired to examine potential interactions between the symbionts and commensal microorganisms of the root microbiota when grown in natural soil. This revealed microbial interkingdom interactions between the root symbionts and fungal as well as bacterial commensal communities. Nevertheless, the bacterial root microbiota remains largely robust when fungal symbiosis is impaired. Our work implies a broad role for host symbiosis genes in structuring the root microbiota of legumes.

The wild legume Lotus japonicus engages in mutualistic symbiotic relationships with arbuscular mycorrhiza (AM) fungi and nitrogen-fixing rhizobia. Using plants grown in natural soil and community profiling of bacterial 16S rRNA genes and fungal internal transcribed spacers (ITSs), we examined the role of the Lotus symbiosis genes RAM1, NFR5, SYMRK, and CCaMK in structuring bacterial and fungal root-associated communities. We found host genotype-dependent community shifts in the root and rhizosphere compartments that were mainly confined to bacteria in nfr5 or fungi in ram1 mutants, while symrk and ccamk plants displayed major changes across both microbial kingdoms. We observed in all AM mutant roots an almost complete depletion of a large number of Glomeromycota taxa that was accompanied by a concomitant enrichment of Helotiales and Nectriaceae fungi, suggesting compensatory niche replacement within the fungal community. A subset of Glomeromycota whose colonization is strictly dependent on the common symbiosis pathway was retained in ram1 mutants, indicating that RAM1 is dispensable for intraradical colonization by some Glomeromycota fungi. However, intraradical colonization by bacteria belonging to the Burkholderiaceae and Anaeroplasmataceae is dependent on AM root infection, revealing a microbial interkingdom interaction. Despite the overall robustness of the bacterial root microbiota against major changes in the composition of root-associated fungal assemblages, bacterial and fungal cooccurrence network analysis demonstrates that simultaneous disruption of AM and rhizobium symbiosis increases the connectivity among taxa of the bacterial root microbiota. Our findings imply a broad role for Lotus symbiosis genes in structuring the root microbiota and identify unexpected microbial interkingdom interactions between root symbionts and commensal communities.

Root extracellular traps versus neutrophil extracellular traps in host defence, a case of functional convergence?

The root cap releases cells that produce massive amounts of mucilage containing polysaccharides, proteoglycans, extracellular DNA (exDNA) and a variety of antimicrobial compounds. The released cells - known as border cells or border-like cells - and mucilage secretions form networks that are defined as root extracellular traps (RETs). RETs are important players in root immunity. In animals, phagocytes are some of the most abundant white blood cells in circulation and are very important for immunity. These cells combat pathogens through multiple defence mechanisms, including the release of exDNA-containing extracellular traps (ETs). Traps of neutrophil origin are abbreviated herein as NETs. Similar to phagocytes, plant root cap-originating cells actively contribute to frontline defence against pathogens. RETs and NETs are thus components of the plant and animal immune systems, respectively, that exhibit similar compositional and functional properties. Herein, we describe and discuss the formation, molecular composition and functional similarities of these similar but different extracellular traps.

Activity in the Arbuscular Mycorrhizal Hyphosphere Warning Neighbouring Plants

Pathogen infections of the phyllosphere have been investigated in detail, however, the changes induced by these infections on the arbuscular mycorrhizal hyphosphere, and the consequent signalling to the neighbouring plants have been scarcely investigated. Here, our objectives were to document that B.fabae infection of connected Vicia faba plants resulted in changes in the metabolism and microbial community of the hyphosphere, confirming the induction of plant defence in connected plants through gene-expression evaluations. Infected plants were challenged with B. fabae for 72 h. Changes in gene-expression of pathogenesis-related proteins 1,2, and 5 (PR1, PR2, PR5) of both infected- and non-infected plants were analysed, to confirm signalling through the hyphosphere. The primary metabolic profiles and changes in the level of microbiota in the hyphosphere were assessed. Changes in expression of PR1, PR2, and PR5 genes occurred in the neighbouring plants 24 hours after infection. Mannitol levels decreased in presence of AMF. A decrease in the level of actinobacteria in the hyphosphere of infected plants was detected. We conclude that B.fabae infection induced a signalling event through the AM hyphosphere, confirmed by changes in defence gene-expression in non-infected neighbouring plants, influenced primary metabolic activity of-, and affected the microbial composition within-, the AM hyphosphere.

Plant volatile emission depends on the species composition of the neighboring plant community

BACKGROUND

Plants grow in multi-species communities rather than monocultures. Yet most studies on the emission of volatile organic compounds (VOCs) from plants in response to insect herbivore feeding focus on one plant species. Whether the presence and identity of neighboring plants or plant community attributes, such as plant species richness and plant species composition, affect the herbivore-induced VOC emission of a focal plant is poorly understood.

METHODS

We established experimental plant communities in pots in the greenhouse where the focal plant species, red clover (Trifolium pratense), was grown in monoculture, in a two species mixture together with Geranium pratense or Dactylis glomerata, or in a mixture of all three species. We measured VOC emission of the focal plant and the entire plant community, with and without herbivory of Spodoptera littoralis caterpillars caged on one red clover individual within the communities.

RESULTS

Herbivory increased VOC emission from red clover, and increasing plant species richness changed emissions of red clover and also from the entire plant community. Neighbor identity strongly affected red clover emission, with highest emission rates for plants growing together with D. glomerata.

CONCLUSION

The results from this study indicate that the blend of VOCs perceived by host searching insects can be affected by plant-plant interactions.

Common mycorrhizal networks influence the distribution of mineral nutrients between an invasive plant, Solidago canadensis, and a native plant, Kummerowa striata

Invasive species often reduce ecosystem services and lead to a serious threat to native biodiversity. Roots of invasive plants are often linked to roots of native plants by common mycorrhizal networks (CMNs) of arbuscular mycorrhizal (AM) fungi, but whether and how CMNs mediate interactions between invasive and native plant species remains largely uninvestigated. We conducted two microcosm experiments, one in which we amended the soil with mineral N and another in which we amended the soil with mineral P. In each experiment, we grew a pair of test plants consisting of Kummerowia striata (native to our research site) and Solidago canadensis (an invasive species). CMNs were established between the plants, and these were either left intact or severed. Intact CMNs increased growth and nutrient acquisition by S. canadensis while they decreased nutrient acquisition by K. striata in comparison with severed CMNs. ¹⁵N and P analyses indicated that compared to severed CMNs, intact CMNs preferentially transferred mineral nutrients to S. canadensis. CMNs produced by different species of AM fungi had slightly different effects on the interaction between these two plant species. These results highlight the role of CMNs in the understanding of interactions between the invasive species S. canadensis and its native neighbor.

Aphid infestation in the phyllosphere affects primary metabolic profiles in the arbuscular mycorrhizal hyphosphere

While effects of (a)biotic stress events in the phyllosphere have been studied intensively, possible influences of stress on the arbuscular mycorrhizal hyphosphere has scarcely been investigated. We hypothesised that stress challenge in the phyllosphere could alter primary metabolite profiles of the hyphosphere - the mycelial network connecting plants. Donor plants, connected to receiver plants by mycelial networks, were aphid-challenged during 84 h. Primary metabolite profiles in the hyphosphere were investigated. Gene-expression of plant defence gene PR1 was measured in one of the receiver plants during the challenge. Hexose levels in the hyphosphere increased when donor plants were aphid-challenged. This change in metabolic profile was influenced by leaf sampling from receiver plant. PR1 expression increased in donor plants 48 h after challenge, and consequently 60 h after, in receiver plants. We conclude that aphid infestation of donor plants modified primary carbon metabolism in the hyphosphere. Plant defence response in receiver plants, occurred 12 h after detection of response in the aphid-challenged donor plants. While this work is the first to reveal primary metabolic profiles of the AM hyphosphere, more work is needed to elucidate the possible role of transient changes of hexose metabolism in stress response and signalling processes in the hyphosphere of connected plants.

Field studies reveal functions of chemical mediators in plant interactions

Plants are at the trophic base of most ecosystems, embedded in a rich network of ecological interactions in which they evolved. While their limited range and speed of motion precludes animal-typical behavior, plants are accomplished chemists, producing thousands of specialized metabolites which may function to convey information, or even to manipulate the physiology of other organisms. Plants' complex interactions and their underlying mechanisms are typically dissected within the controlled environments of growth chambers and glasshouses, but doing so introduces conditions alien to plants evolved in natural environments, such as being pot-bound, and receiving artificial light with a spectrum very different from sunlight. The mechanistic understanding gained from a reductionist approach provides the tools required to query and manipulate plant interactions in real-world settings. The few tests conducted in natural ecosystems and agricultural fields have highlighted the limitations of studying plant interactions only in artificial environments. Here, we focus on three examples of known or hypothesized chemical mediators of plants' interactions: the volatile phytohormone ethylene (ET), more complex plant volatile blends, and as-yet-unknown mediators transferred by common mycorrhizal networks (CMNs). We highlight how mechanistic knowledge has advanced research in all three areas, and the critical importance of field work if we are to put our understanding of chemical ecology on rigorous experimental and theoretical footing, and demonstrate function.

Below-ground-above-ground Plant-microbial Interactions: Focusing on Soybean, Rhizobacteria and Mycorrhizal Fungi

INTRODUCTION

Organisms seldom exist in isolation and are usually involved in interactions with several hosts and these interactions in conjunction with the physicochemical parameters of the soil affect plant growth and development. Researches into below and aboveground microbial community are unveiling a myriad of intriguing interactions within the rhizosphere, and many of the interactions are facilitated by exudates that are secreted by plants roots. These interactions can be harnessed for beneficial use in agriculture to enhance crop productivity especially in semi-arid and arid environments.

THE RHIZOSPHERE

The rhizosphere is the region of soil close to plants roots that contain large number of diverse organisms. Examples of microbial candidates that are found in the rhizosphere include the Arbuscular Mycorrhizal Fungi (AMF) and rhizobacteria. These rhizosphere microorganisms use plant root secretions such as mucilage and flavonoids which are able to influence their diversity and function and also enhance their potential to colonize plants root.

NATURAL INTERACTIONS BETWEEN MICROORGANISMS AND PLANT

In the natural environments, plants live in interactions with different microorganisms, which thrive belowground in the rhizosphere and aboveground in the phyllosphere. Some of the plant-microbial interactions (which can be in the form of antagonism, amensalism, parasitism and symbiosis) protect the host plants against detrimental microbial and non-microbial invaders and provide nutrients for plants while others negatively affect plants. These interactions can influence below-ground-above-ground plants' biomass development thereby playing significant role in sustaining plants. Therefore, understanding microbial interactions within the rhizosphere and phyllosphere is urgent towards farming practices that are less dependent on conventional chemical fertilizers, which have known negative impacts on the environments.

BELOW GROUND RHIZOBACTERIA INTERACTIONS ALLEVIATE DROUGHT STRESS

Drought stress is one of the major factors militating against agricultural productivity globally and is likely to further increase. Belowground rhizobacteria interactions could play important role in alleviating drought stress in plants. These beneficial rhizobacterial colonize the rhizosphere of plants and impart drought tolerance by up regulation or down regulation of drought responsive genes such as ascorbate peroxidase, S-adenosyl-methionine synthetase, and heat shock protein.

INSIGHTS INTO BELOW AND ABOVE THE GROUND MICROBIAL INTERACTIONS VIA OMIC STUDIES

Investigating complex microbial community in the environment is a big challenge. Therefore, omic studies of microorganisms that inhabit the rhizosphere are important since this is where most plant-microbial interactions occur. One of the aims of this review is not to give detailed account of all the present omic techniques, but instead to highlight the current omic techniques that can possibly lead to detection of novel genes and their respective proteins within the rhizosphere which may be of significance in enhancing crop plants (such as soybean) productivity especially in semi-arid and arid environments.

FUTURE PROSPECTS AND CONCLUSIONS

Plant-microbial interactions are not totally understood, and there is, therefore, the need for further studies on these interactions in order to get more insights that may be useful in sustainable agricultural development. With the emergence of omic techniques, it is now possible to effectively monitor transformations in rhizosphere microbial community together with their effects on plant development. This may pave way for scientists to discover new microbial species that will interact effectively with plants. Such microbial species can be used as biofertilizers and/or bio-pesticides to increase crop yield and enhance global food security.

Volatile terpenoids: multiple functions, biosynthesis, modulation and manipulation by genetic engineering

Terpenoids play several physiological and ecological functions in plant life through direct and indirect plant defenses and also in human society because of their enormous applications in the pharmaceutical, food and cosmetics industries. Through the aid of genetic engineering its role can by magnified to broad spectrum by improving genetic ability of crop plants, enhancing the aroma quality of fruits and flowers and the production of pharmaceutical terpenoids contents in medicinal plants. Terpenoids are structurally diverse and the most abundant plant secondary metabolites, playing an important role in plant life through direct and indirect plant defenses, by attracting pollinators and through different interactions between the plants and their environment. Terpenoids are also significant because of their enormous applications in the pharmaceutical, food and cosmetics industries. Due to their broad distribution and functional versatility, efforts are being made to decode the biosynthetic pathways and comprehend the regulatory mechanisms of terpenoids. This review summarizes the recent advances in biosynthetic pathways, including the spatiotemporal, transcriptional and post-transcriptional regulatory mechanisms. Moreover, we discuss the multiple functions of the terpene synthase genes (TPS), their interaction with the surrounding environment and the use of genetic engineering for terpenoid production in model plants. Here, we also provide an overview of the significance of terpenoid metabolic engineering in crop protection, plant reproduction and plant metabolic engineering approaches for pharmaceutical terpenoids production and future scenarios in agriculture, which call for sustainable production platforms by improving different plant traits.

Plant Science View on Biohybrid Development

Biohybrid consists of a living organism or cell and at least one engineered component. Designing robot-plant biohybrids is a great challenge: it requires interdisciplinary reconsideration of capabilities intimate specific to the biology of plants. Envisioned advances should improve agricultural/horticultural/social practice and could open new directions in utilization of plants by humans. Proper biohybrid cooperation depends upon effective communication. During evolution, plants developed many ways to communicate with each other, with animals, and with microorganisms. The most notable examples are: the use of phytohormones, rapid long-distance signaling, gravity, and light perception. These processes can now be intentionally re-shaped to establish plant-robot communication. In this article, we focus on plants physiological and molecular processes that could be used in bio-hybrids. We show phototropism and biomechanics as promising ways of effective communication, resulting in an alteration in plant architecture, and discuss the specifics of plants anatomy, physiology and development with regards to the bio-hybrids. Moreover, we discuss ways how robots could influence plants growth and development and present aims, ideas, and realized projects of plant-robot biohybrids.

Disproportionate photosynthetic decline and inverse relationship between constitutive and induced volatile emissions upon feeding of Quercus robur leaves by large larvae of gypsy moth (Lymantria dispar)

Gypsy moth (Lymantria dispar L., Lymantriinae) is a major pest of pedunculate oak (Quercus robur) forests in Europe, but how its infections scale with foliage physiological characteristics, in particular with photosynthesis rates and emissions of volatile organic compounds has not been studied. Differently from the majority of insect herbivores, large larvae of L. dispar rapidly consume leaf area, and can also bite through tough tissues, including secondary and primary leaf veins. Given the rapid and devastating feeding responses, we hypothesized that infection of Q. robur leaves by L. dispar leads to disproportionate scaling of leaf photosynthesis and constitutive isoprene emissions with damaged leaf area, and to less prominent enhancements of induced volatile release. Leaves with 0% (control) to 50% of leaf area removed by larvae were studied. Across this range of infection severity, all physiological characteristics were quantitatively correlated with the degree of damage, but all these traits changed disproportionately with the degree of damage. The net assimilation rate was reduced by almost 10-fold and constitutive isoprene emissions by more than 7-fold, whereas the emissions of green leaf volatiles, monoterpenes, methyl salicylate and the homoterpene (3E)-4,8-dimethy-1,3,7-nonatriene scaled negatively and almost linearly with net assimilation rate through damage treatments. This study demonstrates that feeding by large insect herbivores disproportionately alters photosynthetic rate and constitutive isoprene emissions. Furthermore, the leaves have a surprisingly large capacity for enhancement of induced emissions even when foliage photosynthetic function is severely impaired.

Nutrient enrichment effects on mycorrhizal fungi in an Andean tropical montane Forest

Nitrogen (N) and phosphorus (P) deposition are increasing worldwide largely due to increased fertilizer use and fossil fuel combustion. Most work with N and P deposition in natural ecosystems has focused on temperate, highly industrialized, regions. Tropical regions are becoming more developed, releasing large amounts of these nutrients into the atmosphere. Nutrient enrichment in nutrient-poor systems such as tropical montane forest can represent a relatively large shift in nutrient availability, especially for sensitive microorganisms such as arbuscular mycorrhizal fungi (AMF). These symbiotic fungi are particularly critical, given their key role in ecosystem processes affecting plant community structure and function.To better understand the consequences of nutrient deposition in plant communities, a long-term nutrient addition experiment was set up in a tropical montane forest in the Andes of southern Ecuador. In this study, we investigated the impacts of 7 years of elevated N and P on AMF root colonization potential (AMF-RCP) through a greenhouse bait plant method in which we quantified root colonization. We also examined the relationship between AMF-RCP and rarefied tree diversity.After 7 years of nutrient addition, AMF-RCP was negatively correlated with soil P, positively correlated with soil N, and positively correlated with rarefied tree diversity. Our results show that AMF in this tropical montane forest are directly affected by soil N and P concentrations, but may also be indirectly impacted by shifts in rarefied tree diversity. Our research also highlights the need to fully understand the benefits and drawbacks of using different sampling methods (e.g., AMF-RCP versus direct root sampling) to robustly examine AMF-plant interactions in the future.

Transfer of 13 C between paired Douglas-fir seedlings reveals plant kinship effects and uptake of exudates by ectomycorrhizas

Processes governing the fixation, partitioning, and mineralization of carbon in soils are under increasing scrutiny as we develop a more comprehensive understanding of global carbon cycling. Here we examined fixation by Douglas-fir seedlings and transfer to associated ectomycorrhizal fungi, soil microbes, and full-sibling or nonsibling neighbouring seedlings. Stable isotope probing with 99% ¹³ C-CO₂ was applied to trace ¹³ C-labelled photosynthate throughout plants, fungi, and soil microbes in an experiment designed to assess the effect of relatedness on ¹³ C transfer between plant pairs. The fixation and transfer of the ¹³ C label to plant, fungal, and soil microbial tissue was examined in biomass and phospholipid fatty acids. After a 6 d chase period, c. 26.8% of the ¹³ C remaining in the system was translocated below ground. Enrichment was proportionally greatest in ectomycorrhizal biomass. The presence of mesh barriers (0.5 or 35 μm) between seedlings did not restrict ¹³ C transfer. Fungi were the primary recipients of ¹³ C-labelled photosynthate throughout the system, representing 60-70% of total ¹³ C-enriched phospholipids. Full-sibling pairs exhibited significantly greater ¹³ C transfer to recipient roots in two of four Douglas-fir families, representing three- and fourfold increases (+ c. 4 μg excess ¹³ C) compared with nonsibling pairs. The existence of a root/mycorrhizal exudation-hyphal uptake pathway was supported.

CO2 studies remain key to understanding a future world

Contents 34 I. 34 II. 36 III. 37 IV. 37 V. 38 38 References 38 SUMMARY: Characterizing plant responses to past, present and future changes in atmospheric carbon dioxide concentration ([CO₂ ]) is critical for understanding and predicting the consequences of global change over evolutionary and ecological timescales. Previous CO₂ studies have provided great insights into the effects of rising [CO₂ ] on leaf-level gas exchange, carbohydrate dynamics and plant growth. However, scaling CO₂ effects across biological levels, especially in field settings, has proved challenging. Moreover, many questions remain about the fundamental molecular mechanisms driving plant responses to [CO₂ ] and other global change factors. Here we discuss three examples of topics in which significant questions in CO₂ research remain unresolved: (1) mechanisms of CO₂ effects on plant developmental transitions; (2) implications of rising [CO₂ ] for integrated plant-water dynamics and drought tolerance; and (3) CO₂ effects on symbiotic interactions and eco-evolutionary feedbacks. Addressing these and other key questions in CO₂ research will require collaborations across scientific disciplines and new approaches that link molecular mechanisms to complex physiological and ecological interactions across spatiotemporal scales.

The Mutualistic Interaction between Plants and Arbuscular Mycorrhizal Fungi

Mycorrhizal fungi belong to several taxa and develop mutualistic symbiotic associations with over 90% of all plant species, from liverworts to angiosperms. While descriptive approaches have dominated the initial studies of these fascinating symbioses, the advent of molecular biology, live cell imaging, and “omics” techniques have provided new and powerful tools to decipher the cellular and molecular mechanisms that rule mutualistic plant-fungus interactions. In this article we focus on the most common mycorrhizal association, arbuscular mycorrhiza (AM), which is formed by a group of soil fungi belonging to Glomeromycota. AM fungi are believed to have assisted the conquest of dry lands by early plants around 450 million years ago and are found today in most land ecosystems. AM fungi have several peculiar biological traits, including obligate biotrophy, intracellular development inside the plant tissues, coenocytic multinucleate hyphae, and spores, as well as unique genetics, such as the putative absence of a sexual cycle, and multiple ecological functions. All of these features make the study of AM fungi as intriguing as it is challenging, and their symbiotic association with most crop plants is currently raising a broad interest in agronomic contexts for the potential use of AM fungi in sustainable production under conditions of low chemical input.

Plant volatile-mediated signalling and its application in agriculture: successes and challenges

856 I. 856 II. 857 III. 858 IV. 859 V. 860 VI. 862 VII. 863 VIII. 864 IX. 866 866 References 866 SUMMARY: The mediation of volatile secondary metabolites in signalling between plants and other organisms has long been seen as presenting opportunities for sustainable crop protection. Initially, exploitation of interactions between plants and other organisms, particularly insect pests, foundered because of difficulties in delivering, sustainably, the signal systems for crop protection. We now have mounting and, in some cases, clear practical evidence for successful delivery by companion cropping or next-generation genetic modification (GM). At the same time, the type of plant signalling being exploited has expanded to signalling from plants to organisms antagonistic to pests, and to plant stress-induced, or primed, plant-to-plant signalling for defence and growth stimulation.