Differential expression of steroid-related genes across electrosensory brain regions in two sexually dimorphic species of electric knifefish.

The production of communication signals can be modulated by hormones acting on the brain regions that regulate these signals. However, less is known about how signal perception is regulated by hormones. The electrocommunication signals of weakly electric fishes are sexually dimorphic, sensitive to hormones, and vary across species. The neural circuits that regulate the production and perception of these signals are also well-characterized, and electric fishes are thus an excellent model to examine the neuroendocrine regulation of sensorimotor mechanisms of communication. We investigated (1) whether steroid-related genes are expressed in sensory brain regions that process communication signals; and (2) whether this expression differs across sexes and species that have different patterns of sexual dimorphism in their signals. Apteronotus leptorhynchus and Apteronotus albifrons produce continuous electric organ discharges (EODs) that are used for communication. Two brain regions, the electrosensory lateral line lobe (ELL) and the dorsal torus semicircularis (TSd), process inputs from electroreceptors to allow fish to detect and discriminate electrocommunication signals. We used qPCR to quantify the expression of genes for two androgen receptors (ar1, ar2), two estrogen receptors (esr1, esr2b), and aromatase (cyp19a1b). Four out of five steroid-related genes were expressed in both sensory brain regions, and their expression often varied between sexes and species. These results suggest that expression of steroid-related genes in the brain may differentially influence how EOD signals are encoded across species and sexes, and that gonadal steroids may coordinately regulate central circuits that control both the production and perception of EODs.

The LysM receptor-like kinase SlLYK10 controls lipochitooligosaccharide signaling in inner cell layers of tomato roots.

Establishment of arbuscular mycorrhiza (AM) relies on a plant signaling pathway that can be activated by fungal chitinic signals such as short chain chitooligosaccharides (CO) and lipo-chitooligosaccharides (LCOs). The tomato LysM receptor-like kinase (LysM RLK) SlLYK10 has high affinity for LCOs and is involved in root colonization by arbuscular mycorrhizal fungi (AMF), however its role in LCO responses has not yet been studied. Here, we show that SlLYK10 proteins produced by the Sllyk10-1 and Sllyk10-2 mutant alleles, which both cause decreases in AMF colonization, and carry mutations in LysM1 and 2 respectively, have similar LCO binding affinities compared to the WT SlLYK10. However, the mutant forms were no longer able to induce cell death in Nicotiana benthamiana when co-expressed with MtLYK3, a Medicago truncatula LCO co-receptor, while they physically interacted with MtLYK3 in co-purification experiments. This suggests that the LysM mutations affect the ability of SlLYK10 to trigger signaling through a potential co-receptor rather than its ability to bind LCOs. Interestingly, tomato lines that contain a calcium (Ca2+) concentration reporter (Genetically Encoded Ca2+ indicators, GECO), showed Ca2+ spiking in response to LCO applications, but this occurred only in inner cell layers of the roots, while short chain COs also induced Ca2+ spiking in the epidermis. Moreover, LCO-induced Ca2+spiking was decreased in Sllyk10-1*GECO plants, suggesting that the decrease in AMF colonization in Sllyk10-1 is due to abnormal LCO signaling.

Molecular mechanisms underlying the signal perception and transduction during seed germination.

QuerySeed germination is a vital step in the life cycle of a plant, playing a significant role in seedling establishment and crop yield potential. It is also an important factor in the conservation of plant germplasm resources. This complex process is influenced by a myriad of factors, including environmental conditions, the genetic makeup of the seed, and endogenous hormones. The perception of these environmental signals triggers a cascade of intricate signal transduction events that determine whether a seed germinates or remains dormant. Despite considerable progress in uncovering the molecular mechanisms governing these processes, many questions remain unanswered. In this review, we summarize the current progress in the molecular mechanisms underlying the perception of environmental signals and consequent signal transduction during seed germination, and discuss questions that need to be addressed to better understand the process of seed germination and develop novel strategies for germplasm improvement.

cis-DA-dependent dispersion by Pseudomonas aeruginosa biofilm and identification of cis-DA-sensory protein DspS.

IMPORTANCE: Dispersion is an essential stage of the biofilm life cycle resulting in the release of bacteria from a biofilm into the surrounding environment. Dispersion contributes to bacterial survival by relieving overcrowding within a biofilm and allowing dissemination of cells into new habitats for colonization. Thus, dispersion can contribute to biofilm survival as well as disease progression and transmission. Cells dispersed from a biofilm rapidly lose their recalcitrant antimicrobial-tolerant biofilm phenotype and transition to a state that is susceptible to antibiotics. However, much of what is known about this biofilm developmental stage has been inferred from exogenously induced dispersion. Our findings provide the first evidence that native dispersion is coincident with reduced cyclic dimeric guanosine monophosphate levels, while also relying on at least some of the same factors that are central to the environmentally induced dispersion response, namely, BdlA, DipA, RbdA, and AmrZ. Additionally, we demonstrate for the first time that cis-DA signaling to induce dispersion is attributed to the two-component sensor/response regulator DspS, a homolog of the DSF sensor RpfC. Our findings also provide a path toward manipulating the native dispersion response as a novel and highly promising therapeutic intervention.

Synthesis and signalling of strigolactone and KAI2-ligand signals in bryophytes.

Strigolactones (SLs), long known as butenolide rhizospheric signals, have been recognized since 2008 as a class of hormones regulating many aspects of plant development. Many authors also anticipate 'KAI2-ligand' (KL) as a novel class of phytohormones; however, this ligand remains elusive. Core genes of SL and KL pathways, first described in angiosperms, are found in all land plants and some even in green algae. This review reports current knowledge of these pathways in bryophytes. Data on the pathways mostly come from two models: the moss Physcomitrium patens and the liverwort Marchantia. Gene targeting methods have allowed functional analyses of both models. Recent work in Marchantia suggests that SLs' ancestral role was to recruit beneficial microbes as arbuscular mycorrhizal fungi. In contrast, the hormonal role of SLs observed in P. patens is probably a result of convergent evolution. Evidence for a functional KL pathway in both bryophyte models is very recent. Nevertheless, many unknowns remain and warrant a more extensive investigation of SL and KL pathways in various land plant lineages.

Parasitic Plants: An Overview of Mechanisms by Which Plants Perceive and Respond to Parasites.

In contrast to most autotrophic plants, which produce carbohydrates from carbon dioxide using photosynthesis, parasitic plants obtain water and nutrients by parasitizing host plants. Many important crop plants are infested by these heterotrophic plants, leading to severe agricultural loss and reduced food security. Understanding how host plants perceive and resist parasitic plants provides insight into underlying defense mechanisms and the potential for agricultural applications. In this review, we offer a comprehensive overview of the current understanding of host perception of parasitic plants and the pre-attachment and post-attachment defense responses mounted by the host. Since most current research overlooks the role of organ specificity in resistance responses, we also summarize the current understanding and cases of cross-organ parasitism, which indicates nonconventional haustorial connections on other host organs, for example, when stem parasitic plants form haustoria on their host roots. Understanding how different tissue types respond to parasitic plants could provide the potential for developing a universal resistance mechanism in crops against both root and stem parasitic plants.

Feeling the Heat: The Campylobacter jejuni HrcA Transcriptional Repressor Is an Intrinsic Protein Thermosensor.

The heat-shock response, a universal protective mechanism consisting of a transcriptional reprogramming of the cellular transcriptome, results in the accumulation of proteins which counteract the deleterious effects of heat-stress on cellular polypeptides. To quickly respond to thermal stress and trigger the heat-shock response, bacteria rely on different mechanisms to detect temperature variations, which can involve nearly all classes of biological molecules. In Campylobacter jejuni the response to heat-shock is transcriptionally controlled by a regulatory circuit involving two repressors, HspR and HrcA. In the present work we show that the heat-shock repressor HrcA acts as an intrinsic protein thermometer. We report that a temperature upshift up to 42 °C negatively affects HrcA DNA-binding activity to a target promoter, a condition required for de-repression of regulated genes. Furthermore, we show that this impairment of HrcA binding at 42 °C is irreversible in vitro, as DNA-binding was still not restored by reversing the incubation temperature to 37 °C. On the other hand, we demonstrate that the DNA-binding activity of HspR, which controls, in combination with HrcA, the transcription of chaperones' genes, is unaffected by heat-stress up to 45 °C, portraying this master repressor as a rather stable protein. Additionally, we show that HrcA binding activity is enhanced by the chaperonin GroE, upon direct protein-protein interaction. In conclusion, the results presented in this work establish HrcA as a novel example of intrinsic heat-sensing transcriptional regulator, whose DNA-binding activity is positively modulated by the GroE chaperonin.

Convergence and Divergence: Signal Perception and Transduction Mechanisms of Cold Stress in Arabidopsis and Rice.

Cold stress, including freezing stress and chilling stress, is one of the major environmental factors that limit the growth and productivity of plants. As a temperate dicot model plant species, Arabidopsis develops a capability to freezing tolerance through cold acclimation. The past decades have witnessed a deep understanding of mechanisms underlying cold stress signal perception, transduction, and freezing tolerance in Arabidopsis. In contrast, a monocot cereal model plant species derived from tropical and subtropical origins, rice, is very sensitive to chilling stress and has evolved a different mechanism for chilling stress signaling and response. In this review, the authors summarized the recent progress in our understanding of cold stress response mechanisms, highlighted the convergent and divergent mechanisms between Arabidopsis and rice plasma membrane cold stress perceptions, calcium signaling, phospholipid signaling, MAPK cascade signaling, ROS signaling, and ICE-CBF regulatory network, as well as light-regulated signal transduction system. Genetic engineering approaches of developing freezing tolerant Arabidopsis and chilling tolerant rice were also reviewed. Finally, the future perspective of cold stress signaling and tolerance in rice was proposed.

SEM analysis of sensilla on the mouthparts and antennae of Asian larch bark beetle Ips subelongatus.

The Asian larch bark beetle, Ips subelongatus, is a severe pest of larches in Northeastern China. The gustatory and olfactory systems of I. subelongatus play important roles in host location, mating, and feeding. In this study, we examined the types, distributions, and abundances of various sensilla associated with the mouthparts and antennae of I. subelongatus using scanning electron microscopy (SEM). On the mouthparts, five types of sensilla are present: sensilla trichodea (S.t.1-3), sensilla chaetica (S.c.1-3), sensilla basiconica (S.b.1-2), sensilla twig basiconica (S.tb.1-3), and sensilla placodea (S.p). S.t.3 are the most abundant sensilla subtype on the mouthparts in both sexes, while S.b.1 are the least abundant. Most sensilla on the mouthparts are located on the maxillae and labium, and the apex of each maxillary and labial palp carry the same sensilla subtypes (S.b.2 and S.tb.1-3). However, the total number of sensilla on the apex of each maxillary palp is higher than that on the labial palp. On the antennae, five types of sensilla are present: sensilla trichodea (S.t.1-3), sensilla chaetica (S.c.1-2), sensilla basiconica (S.b.1-3), Böhm bristles (B.b), and sensilla coeloconica (S.co). Antennal sensilla are mostly situated on the anterior surface of the antennal club, particularly on the two dense sensory bands. S.b.1 are the most abundant sensilla subtype on the antennae in both sexes, while S.t.1 are the least abundant. No sexual dimorphism in sensilla type or distribution on the mouthparts or antennae is observed between the sexes of I. subelongatus. However, S.t.3 (on mouthparts) and S.c.1 (on antennae) were significantly more abundant in males than in females, while more S.t.1 (on mouthparts) were observed in females than in males. Finally, the putative functions of each kind of sensilla with respect to their fine structures, distributions, and abundances on the mouthparts and antennae are discussed.

MCA1 and MCA2 Are Involved in the Response to Hypergravity in Arabidopsis Hypocotyls.

Plants respond to and resist gravitational acceleration, but the mechanism of signal perception in the response is unknown. We studied the role of MCA (mid1-complementing activity) proteins in gravity perception by analyzing the expression of the MCA1 and MCA2 genes, and the growth of hypocotyls of mca mutants, under hypergravity conditions in the dark. An MCA1 promoter::GUS fusion reporter gene construct (MCA1p::GUS) and MCA2p::GUS were expressed almost universally in etiolated seedlings. Under hypergravity conditions, the expression levels of both genes increased compared with that under the 1 g condition, and remained higher, especially in the basal supporting region. On the other hand, mca-null and MCA-overexpressing seedlings showed normal growth under the 1 g condition. Hypergravity suppressed elongation growth of hypocotyls, but this effect was reduced in hypocotyls of mca-null mutants compared with the wild type. In contrast, MCA-overexpressing seedlings were hypersensitive to increased gravity; suppression of elongation growth was detected at a lower gravity level than that in the wild type. These results suggest that MCAs are involved in the perception of gravity signals in plants, and may be responsible for resistance to hypergravity.

Ethanol, at physiological concentrations, affects ethylene sensing in tomato germinating seeds and seedlings.

Ethanol is known to accumulate in various plant organs under various environmental conditions. However, there are very scarce data about ethanol sensing by plants. We observed that ethanol accumulates up to 3.5 mM during tomato seed imbibition, particularly when seeds were stacked. Stacked seeds germinated less than spread out seeds suggesting ethanol inhibits germination. In support of this, exogenous ethanol at physiological concentrations, ranging from 1 to 10 mM, inhibited germination of wild type tomato seeds. However, the germination pattern over the whole ethanol concentration range tested was modified in an ethylene insensitive mutant, never-ripe (nr). The effects of exogenous ethanol were not linked to differences in ethylene production by imbibed seeds. But, we observed that exogenous ethanol at a concentration as low as 0.01 mM down regulated the expression of some ethylene receptors. Moreover, the triple response induced by ethylene in tomato seedlings was partially alleviated by 1 mM ethanol. Similar observations were made on Arabidopsis seeds. These results show there are interactions between ethylene sensing and ethanol in plants.

Binding or Hydrolysis? How Does the Strigolactone Receptor Work?

The strigolactone (SL) receptor in plants is unusual in that it both binds and hydrolyses SL molecules. Landmark studies had proposed that a product of hydrolysis irreversibly binds the receptor and then activates signalling. However, recent breakthrough articles (Seto et al. Nat. Commun. 2019;10:191 and Shabek et al. Nature 2018;563:652-656) have revealed a new model based on inhibition of hydrolysis by protein conformation.

Insect Antennal Morphology: The Evolution of Diverse Solutions to Odorant Perception.

Chemical communication involves the production, transmission, and perception of odors. Most adult insects rely on chemical signals and cues to locate food resources, oviposition sites or reproductive partners and, consequently, numerous odors provide a vital source of information. Insects detect these odors with receptors mostly located on the antennae, and the diverse shapes and sizes of these antennae (and sensilla) are both astonishing and puzzling: what selective pressures are responsible for these different solutions to the same problem - to perceive signals and cues? This review describes the selection pressures derived from chemical communication that are responsible for shaping the diversity of insect antennal morphology. In particular, we highlight new technologies and techniques that offer exciting opportunities for addressing this surprisingly neglected and yet crucial component of chemical communication.

The use of self-report measures to examine changes in perception in response to fittings using different signal processing parameters.

Clinicians have long used self-report methods to assess hearing aid benefit. However, there are fewer data as to whether self-report instruments can be used to compare differences between signal processing settings. This study examined how self-perceived performance varied as a function of modifications in signal processing using two self-report measures. Data were collected as part of a double-blind randomised crossover clinical trial. Participants were fit with two fittings: mild processing (slow time constants, disabled frequency lowering) and strong processing (fast time constants, frequency lowering enabled). The speech, spatial, and qualities of hearing (SSQ) questionnaire and the Effectiveness of Auditory Rehabilitation (EAR) questionnaire were collected at multiple time points. Older adults with sensorineural hearing loss who had not used hearing aids within the previous year participated (49 older adults were consented; 40 were included in the final data analyses). Findings show that listeners report a difference in perceived performance when hearing aid features are modified. Both self-report measures were able to capture this change in perceived performance. Self-report measures provide a tool for capturing changes in perceived performance when hearing aid processing features are modified and may enhance provision of an evidence-based hearing aid fitting.

Queen Control or Queen Signal in Ants: What Remains of the Controversy 25 Years After Keller and Nonacs' Seminal Paper?

Ant queen pheromones (QPs) have long been known to affect colony functioning. In many species, QPs affect important reproductive functions such as diploid larvae sexualization and egg-laying by workers, unmated queens (gynes), or other queens. Until the 1990s, these effects were generally viewed to be the result of queen manipulation through the use of coercive or dishonest signals. However, in their seminal 1993 paper, Keller and Nonacs challenged this idea, suggesting that QPs had evolved as honest signals that informed workers and other colony members of the queen's presence and reproductive state. This paper has greatly influenced the study of ant QPs and inspired numerous attempts to identify fertility-related compounds and test their physiological and behavioral effects. In the present article, we review the literature on ant QPs in various contexts and pay special attention to the role of cuticular hydrocarbons (CHCs). Although the controversy generated by Keller and Nonacs' (Anim Behav 45:787-794, 1993) paper is currently less intensively debated, there is still no clear evidence which allows the rejection of the queen control hypothesis in favor of the queen signal hypothesis. We argue that important questions remain regarding the mode of action of QPs, and their targets which may help understanding their evolution.

Reactive Oxygen Species in Plant Signaling.

As fixed organisms, plants are especially affected by changes in their environment and have consequently evolved extensive mechanisms for acclimation and adaptation. Initially considered by-products from aerobic metabolism, reactive oxygen species (ROS) have emerged as major regulatory molecules in plants and their roles in early signaling events initiated by cellular metabolic perturbation and environmental stimuli are now established. Here, we review recent advances in ROS signaling. Compartment-specific and cross-compartmental signaling pathways initiated by the presence of ROS are discussed. Special attention is dedicated to established and hypothetical ROS-sensing events. The roles of ROS in long-distance signaling, immune responses, and plant development are evaluated. Finally, we outline the most challenging contemporary questions in the field of plant ROS biology and the need to further elucidate mechanisms allowing sensing, signaling specificity, and coordination of multiple signals.

Combinatorial Signal Perception in the BMP Pathway.

The bone morphogenetic protein (BMP) signaling pathway comprises multiple ligands and receptors that interact promiscuously with one another and typically appear in combinations. This feature is often explained in terms of redundancy and regulatory flexibility, but it has remained unclear what signal-processing capabilities it provides. Here, we show that the BMP pathway processes multi-ligand inputs using a specific repertoire of computations, including ratiometric sensing, balance detection, and imbalance detection. These computations operate on the relative levels of different ligands and can arise directly from competitive receptor-ligand interactions. Furthermore, cells can select different computations to perform on the same ligand combination through expression of alternative sets of receptor variants. These results provide a direct signal-processing role for promiscuous receptor-ligand interactions and establish operational principles for quantitatively controlling cells with BMP ligands. Similar principles could apply to other promiscuous signaling pathways.

Alternative splicing of the receptor-like kinase Nt-Sd-RLK in tobacco cells responding to lipopolysaccharides: suggestive of a role in pathogen surveillance and perception?

Nt-Sd-RLK encodes an S-domain lectin receptor-like kinase that is induced in response to microbe-associated molecular pattern molecules (MAMPs) such as lipopolysaccharide (LPS). In this study, we investigated the alternative splicing of Nt-Sd-RLK in response to LPS stimulation. Our data indicate that in nonstimulated cells, a shorter transcript of Nt-Sd-RLK is generated and that in response to LPS, alternative splicing produces the full-length transcript. We propose that the extracellular domain of Nt-Sd-RLK encoded by the shorter transcript functions in pathogen surveillance. Once this domain binds LPS, alternative splicing generates the kinase domain-containing Nt-Sd-RLK that activates downstream signalling leading to a defence response. Thus, our findings suggest that plant defence signalling may be regulated through the alternative splicing of receptor-like kinases involved in pathogen recognition.

Perception and Signaling of Strigolactones.

Strigolactones (SLs), a recently discovered class of phytohormones, are important regulators of plant growth and development. While the biosynthetic pathway of these molecules is well documented, until recently there was not much known about the molecular mechanisms underlying SL perception and signal transduction in plants. Certain aspects of their perception and signaling, including the hormone-mediated interaction between receptor and F-box protein, degradation of suppressor proteins and activation of transcription factors, are also found in other phytohormones. However, some of SL signaling features seem to be specific for the SL signaling pathway. These include the enzymatic activity of the SL receptor and its destabilization caused by SLs. This review summarizes the current knowledge about SL signaling pathway in plants.

Oxidative post-translational modifications of cysteine residues in plant signal transduction.

In plants, fluctuation of the redox balance by altered levels of reactive oxygen species (ROS) can affect many aspects of cellular physiology. ROS homeostasis is governed by a diversified set of antioxidant systems. Perturbation of this homeostasis leads to transient or permanent changes in the redox status and is exploited by plants in different stress signalling mechanisms. Understanding how plants sense ROS and transduce these stimuli into downstream biological responses is still a major challenge. ROS can provoke reversible and irreversible modifications to proteins that act in diverse signalling pathways. These oxidative post-translational modifications (Ox-PTMs) lead to oxidative damage and/or trigger structural alterations in these target proteins. Characterization of the effect of individual Ox-PTMs on individual proteins is the key to a better understanding of how cells interpret the oxidative signals that arise from developmental cues and stress conditions. This review focuses on ROS-mediated Ox-PTMs on cysteine (Cys) residues. The Cys side chain, with its high nucleophilic capacity, appears to be the principle target of ROS. Ox-PTMs on Cys residues participate in various signalling cascades initiated by plant stress hormones. We review the mechanistic aspects and functional consequences of Cys Ox-PTMs on specific target proteins in view of stress signalling events.