In terrestrial ecosystems, plants take up phosphate predominantly via association with arbuscular mycorrhizal fungi (AMF). We identified loss of responsiveness to AMF in the rice (Oryza sativa) ...mutant hebiba, reflected by the absence of physical contact and of characteristic transcriptional responses to fungal signals. Among the 26 genes deleted in hebiba, DWARF 14 LIKE is, the one responsible for loss of symbiosis. It encodes an alpha/beta-fold hydrolase, that is a component of an intracellular receptor complex involved in the detection of the smoke compound karrikin. Our finding reveals an unexpected plant recognition strategy for AMF and a previously unknown signaling link between symbiosis and plant development.
Mycorrhizal symbioses-the union of roots and soil fungi-are universal in terrestrial ecosystems and may have been fundamental to land colonization by plants. Boreal, temperate and montane forests all ...depend on ectomycorrhizae. Identification of the primary factors that regulate symbiotic development and metabolic activity will therefore open the door to understanding the role of ectomycorrhizae in plant development and physiology, allowing the full ecological significance of this symbiosis to be explored. Here we report the genome sequence of the ectomycorrhizal basidiomycete Laccaria bicolor (Fig. 1) and highlight gene sets involved in rhizosphere colonization and symbiosis. This 65-megabase genome assembly contains ∼20,000 predicted protein-encoding genes and a very large number of transposons and repeated sequences. We detected unexpected genomic features, most notably a battery of effector-type small secreted proteins (SSPs) with unknown function, several of which are only expressed in symbiotic tissues. The most highly expressed SSP accumulates in the proliferating hyphae colonizing the host root. The ectomycorrhizae-specific SSPs probably have a decisive role in the establishment of the symbiosis. The unexpected observation that the genome of L. bicolor lacks carbohydrate-active enzymes involved in degradation of plant cell walls, but maintains the ability to degrade non-plant cell wall polysaccharides, reveals the dual saprotrophic and biotrophic lifestyle of the mycorrhizal fungus that enables it to grow within both soil and living plant roots. The predicted gene inventory of the L. bicolor genome, therefore, points to previously unknown mechanisms of symbiosis operating in biotrophic mycorrhizal fungi. The availability of this genome provides an unparalleled opportunity to develop a deeper understanding of the processes by which symbionts interact with plants within their ecosystem to perform vital functions in the carbon and nitrogen cycles that are fundamental to sustainable plant productivity.
In a striking display of trans-kingdom symbiosis, gut bacteria cooperate with their animal hosts to regulate the development and function of the immune, metabolic and nervous systems through dynamic ...bidirectional communication along the 'gut-brain axis'. These processes may affect human health, as certain animal behaviours appear to correlate with the composition of gut bacteria, and disruptions in microbial communities have been implicated in several neurological disorders. Most insights about host-microbiota interactions come from animal models, which represent crucial tools for studying the various pathways linking the gut and the brain. However, there are complexities and manifest limitations inherent in translating complex human disease to reductionist animal models. In this Review, we discuss emerging and exciting evidence of intricate and crucial connections between the gut microbiota and the brain involving multiple biological systems, and possible contributions by the gut microbiota to neurological disorders. Continued advances from this frontier of biomedicine may lead to tangible impacts on human health.
Soil salinization adversely affects plant growth and has become one of the major limiting factors for crop productivity worldwide. The conventional approach, breeding salt-tolerant plant cultivars, ...has often failed to efficiently alleviate the situation. In contrast, the use of a diverse array of microorganisms harbored by plants has attracted increasing attention because of the remarkable beneficial effects of microorganisms on plants. Multiple advanced '-omics' technologies have enabled us to gain insights into the structure and function of plant-associated microbes. In this review, we first focus on microbe-mediated plant salt tolerance, in particular on the physiological and molecular mechanisms underlying root-microbe symbiosis. Unfortunately, when introducing such microbes as single strains to soils, they are often ineffective in improving plant growth and stress tolerance, largely due to competition with native soil microbial communities and limited colonization efficiency. Rapid progress in rhizosphere microbiome research has revived the belief that plants may benefit more from association with interacting, diverse microbial communities (microbiome) than from individual members in a community. Understanding how a microbiome assembles in the continuous compartments (endosphere, rhizoplane, and rhizosphere) will assist in predicting a subset of core or minimal microbiome and thus facilitate synthetic re-construction of microbial communities and their functional complementarity and synergistic effects. These developments will open a new avenue for capitalizing on the cultivable microbiome to strengthen plant salt tolerance and thus to refine agricultural practices and production under saline conditions.
Rhizobia are bacteria that form nitrogen-fixing nodules in legume plants. The sets of genes responsible for both nodulation and nitrogen fixation are carried in plasmids or genomic islands that are ...often mobile. Different strains within a species sometimes have different host specificities, while very similar symbiosis genes may be found in strains of different species. These specificity variants are known as symbiovars, and many of them have been given names, but there are no established guidelines for defining or naming them. Here, we discuss the requirements for guidelines to describe symbiovars, propose a set of guidelines, provide a list of all symbiovars for which descriptions have been published so far, and offer a mechanism to maintain a list in the future.
Bacterial accessory genes are genomic symbionts with an evolutionary history and future that is different from that of their hosts. Packages of accessory genes move from strain to strain and confer ...important adaptations, such as interaction with eukaryotes. The ability to fix nitrogen with legumes is a remarkable example of a complex trait spread by horizontal transfer of a few key symbiotic genes, converting soil bacteria into legume symbionts. Rhizobia belong to hundreds of species restricted to a dozen genera of the Alphaproteobacteria and Betaproteobacteria, suggesting infrequent successful transfer between genera but frequent successful transfer within genera. Here we review the genetic and environmental conditions and selective forces that have shaped evolution of this complex symbiotic trait.
Plant sap-feeding insects (Hemiptera) rely on bacterial symbionts for nutrition absent in their diets. These bacteria experience extreme genome reduction and require genetic resources from their ...hosts, particularly for basic cellular processes other than nutrition synthesis. The host-derived mechanisms that complete these processes have remained poorly understood. It is also unclear how hosts meet the distinct needs of multiple bacterial partners with differentially degraded genomes. To address these questions, we investigated the cell-specific gene-expression patterns in the symbiotic organs of the aster leafhopper (ALF), Macrosteles quadrilineatus (Cicadellidae). ALF harbors two intracellular symbionts that have two of the smallest known bacterial genomes: Nasuia (112 kb) and Sulcia (190 kb). Symbionts are segregated into distinct host cell types (bacteriocytes) and vary widely in their basic cellular capabilities. ALF differentially expresses thousands of genes between the bacteriocyte types to meet the functional needs of each symbiont, including the provisioning of metabolites and support of cellular processes. For example, the host highly expresses genes in the bacteriocytes that likely complement gene losses in nucleic acid synthesis, DNA repair mechanisms, transcription, and translation. Such genes are required to function in the bacterial cytosol. Many host genes comprising these support mechanisms are derived from the evolution of novel functional traits via horizontally transferred genes, reassigned mitochondrial support genes, and gene duplications with bacteriocyte-specific expression. Comparison across other hemipteran lineages reveals that hosts generally support the incomplete symbiont cellular processes, but the origins of these support mechanisms are generally specific to the host–symbiont system.
Summary
Early gene expression in arbuscular mycorrhiza (AM) and the nitrogen‐fixing root nodule symbiosis (RNS) is governed by a shared regulatory complex. Yet many symbiosis‐induced genes are ...specifically activated in only one of the two symbioses.
The Lotus japonicus T‐DNA insertion line T90, carrying a promoterless uidA (GUS) gene in the promoter of Calcium Binding Protein 1 (CBP1) is exceptional as it exhibits GUS activity in both root endosymbioses. To identify the responsible cis‐ and trans‐acting factors, we subjected deletion/modification series of CBP1 promoter : reporter fusions to transactivation and spatio‐temporal expression analysis and screened ethyl methanesulphonate (EMS)‐mutagenized T90 populations for aberrant GUS expression.
We identified one cis‐regulatory element required for GUS expression in the epidermis and a second element, necessary and sufficient for transactivation by the calcium and calmodulin‐dependent protein kinase (CCaMK) in combination with the transcription factor Cyclops and conferring gene expression during both AM and RNS. Lack of GUS expression in T90 white mutants could be traced to DNA hypermethylation detected in and around this element.
We concluded that the CCaMK/Cyclops complex can contribute to at least three distinct gene expression patterns on its direct target promoters NIN (RNS), RAM1 (AM), and CBP1 (AM and RNS), calling for yet‐to‐be identified specificity‐conferring factors.
Mycorrhizal fungi considerably improve plant nutrition and help them to cope with changing environments. Particularly, these fungi express proteins to transfer inorganic phosphate (Pi) from the soil ...to colonized roots through symbiotic interfaces. The mechanisms involved in Pi transfer from fungal to plant cells are still largely unknown. Here, we discuss the recent progress made on the description of these mechanisms and we propose the most promising hypotheses and alternative mechanisms for this process. Specifically, we present a phylogenetic survey of candidate Pi transporters of mycorrhizal fungi that might ensure Pi unload into the symbiotic interfaces. Gathering additional knowledge on mycorrhizal Pi transport will improve the Pi-useefficiency in agroecological systems and will guide towards addressing future research challenges.
The acquisition of phosphorus by plants is often mediated by soil microbes colonizing the roots, particularly mycorrhizal fungi.Key molecular mechanisms involved in the transport of phosphorus from the soil to mycorrhizal fungi have been revealed recently. However, the release of phosphorus towards colonized roots is still understudied, even if a recent report highlighted the possible involvement of fungal H+:Pi transporters.Based on a survey of fungal transport proteins, others mechanisms possibly ensuring phosphorus efflux in mycorrhizas must coexist besides H+:Pi transporters. These include the putative involvement of Pi :Na+, low-affinity inorganic phosphate, and organic phosphate transporters.Unravelling the fungal phosphorus transportome will allow a better use of plant–fungus symbioses for the improvement of plant nutrition in cropping systems.
Symbiotic Metamaterials
In article number 2214580, Il‐Kwon Oh and co‐workers, design a novel symbiotic metamaterial by combining a biomimetic Schwarz minimal surface with a biophilic material from ...nature such as organic lichen. Lichen is a symbiotic fungi that originated in Scandinavian forests with misty climates. This symbiotic lichen Schwarz metamaterial has applications in sound wave manipulation and humidity control for buildings, sustainable architecture, and functional furniture.
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