The Arabidopsis CERK1-associated kinase PBL27 connects chitin perception to MAPK activation

Innate extracellular Hsp70 inflammatory properties are mediated by the interaction of Siglec-E and LOX-1 receptors

Innate immune responses to cell damage-associated molecular patterns induce a controlled degree of inflammation, ideally avoiding the promotion of intense unwanted inflammatory adverse events. When released by damaged cells, Hsp70 can stimulate different responses that range from immune activation to immune suppression. The effects of Hsp70 are mediated through innate receptors expressed primarily by myeloid cells, such as dendritic cells (DCs). The regulatory innate receptors that bind to extracellular mouse Hsp70 (mHsp70) are not fully characterized, and neither are their potential interactions with activating innate receptors. Here, we describe that extracellular mHsp70 interacts with a receptor complex formed by inhibitory Siglec-E and activating LOX-1 on DCs. We also find that this interaction takes place within lipid microdomains, and Siglec-E acts as a negative regulator of LOX-1-mediated innate activation upon mHsp70 or oxidized LDL binding. Thus, HSP70 can both bind to and modulate the interaction of inhibitory and activating innate receptors on the cell surface. These findings add another dimension of regulatory mechanism to how self-molecules contribute to dampening of exacerbated inflammatory responses.

Brachypodium BdCHS is a homolog of Arabidopsis AtCHS involved in the synthesis of flavonoids and lateral root development

Flavonoids are a kind of plant-specific secondary metabolites, which play an important role in regulating plant growth and development, stress response, and also have medicinal value. Chalcone synthase is the key enzyme in the synthesis of flavonoids. The function of chalcone synthase in Arabidopsis thaliana has been well studied, but its homologous protein in Brachypodium distachyon has not been reported. In this study, we identified a homolog of AtCHS in B. distachyon, named BdCHS, and described its function. Phylogenetic tree analysis showed that BdCHS was most closely related to CHS in Triticum aestivum. Transgene analysis revealed that BdCHS protein was localized in the cytoplasm of Arabidopsis root cells. BdCHS protein can complement the phenotype of AtCHS mutants with lighter seed coat color and increased lateral root density. The content of superoxide anion in the cortical cells above the lateral root primordium in AtCHS mutants was higher than that in the wild-type, and BdCHS protein could restore the content of superoxide anion in AtCHS mutant to the level of that in the wild-type. The results showed that BdCHS was a functional homolog of AtCHS, which laid a foundation for the subsequent application of BdCHS in genetic breeding and crop improvement.

Molecular Chaperone Receptors: An Update

Extracellular heat shock proteins (HSP) play important roles in cell signaling and immunity. Many of these effects are mediated by surface receptors expressed on a wide range of cell types, including immune cells. We have investigated the nature of such proteins by cloning candidate receptors into cells (CHO-K1) with the rare property of being null for HSP binding. Using this approach, we have discovered that mammalian and eukaryotic Hsp70 binds avidly to at least three classes of receptor including: (1) c-type lectin receptors (CLR), (2) scavenger receptors (SR) and (3) lectins. However, the structural nature of the receptor-ligand interactions is not currently clear. Hsp70 can bind to LOX-1 (a member of both the CLR and SR), with the c-type lectin binding domain (CTLD), to the SR family members SREC-I and FEEL-1/CLEVER-1/STABILIN-1, which by contrast have arrays of EGF-like repeats in their extracellular domains as well. In this chapter, we will discuss: (1) methods for the discovery of HSP receptors, (2) approaches to the study of individual receptors in cells that contain multiple such receptors and (3) methods for investigating HSP receptor function in vivo.

Relevance and Regulation of Alternative Splicing in Plant Heat Stress Response: Current Understanding and Future Directions

Alternative splicing (AS) is a major mechanism for gene expression in eukaryotes, increasing proteome diversity but also regulating transcriptome abundance. High temperatures have a strong impact on the splicing profile of many genes and therefore AS is considered as an integral part of heat stress response. While many studies have established a detailed description of the diversity of the RNAome under heat stress in different plant species and stress regimes, little is known on the underlying mechanisms that control this temperature-sensitive process. AS is mainly regulated by the activity of splicing regulators. Changes in the abundance of these proteins through transcription and AS, post-translational modifications and interactions with exonic and intronic cis-elements and core elements of the spliceosomes modulate the outcome of pre-mRNA splicing. As a major part of pre-mRNAs are spliced co-transcriptionally, the chromatin environment along with the RNA polymerase II elongation play a major role in the regulation of pre-mRNA splicing under heat stress conditions. Despite its importance, our understanding on the regulation of heat stress sensitive AS in plants is scarce. In this review, we summarize the current status of knowledge on the regulation of AS in plants under heat stress conditions. We discuss possible implications of different pathways based on results from non-plant systems to provide a perspective for researchers who aim to elucidate the molecular basis of AS under high temperatures.

Porcine Gasdermin D Is a Substrate of Caspase-1 and an Executioner of Pyroptosis

Gasdermin (GSDM) family proteins were recently identified as the executioner of pyroptosis. The mechanism of pyroptosis mediated by gasdermin D (GSDMD) (a member of GSDM family) in humans and mice is well understood. In pyroptosis, mouse and human GSDMDs are cleaved by activated proinflammatory caspases (caspase-1, 4, 5, or 11) to produce anamino-terminal domain (GSDMD-NT) and a carboxyl-terminal domain (GSDMD-CT). The GSDMD-NT drives cell membrane rupture, which leads to the pyroptotic death of the cells. The expression of porcine GSDMD (pGSDMD) has recently been determined, but the activation and regulation mechanism of pGSDMD and its ability to mediate pyroptosis are largely unknown. In the present study, the activation of porcine caspase-1 (pcaspase-1) and cleavage of pGSDMD occurred in the duodenum and jejunum of a piglet challenged with enterotoxigenic Escherichia coli were first determined. Then the capability of pcaspase-1 to cleave pGSDMD was determined in a cell-free system and in human embryonic kidney cells. The pGSDMD cleavage by pcaspase-1 occurred after the pGSDMD molecule’s ₂₇₆Phenylalanine-Glutamine-Serine-Aspartic acid₂₇₉ motif. The pGSDMD-NT generated from the pGSDMD cleavage by pcaspase-1 showed the ability to drive cell membrane rupture in eukaryotic cells. When expressed in E. coli competent cells, pGSDMD-NT showed bactericidal activity. These results suggest that pGSDMD is a substate of pcaspase-1 and an executioner of pyroptosis. Our work sheds light on pGSDMD’s activation mechanisms and functions.

An Epigenetic Alphabet of Crop Adaptation to Climate Change

Crop adaptation to climate change is in a part attributed to epigenetic mechanisms which are related to response to abiotic and biotic stresses. Although recent studies increased our knowledge on the nature of these mechanisms, epigenetics remains under-investigated and still poorly understood in many, especially non-model, plants, Epigenetic modifications are traditionally divided into two main groups, DNA methylation and histone modifications that lead to chromatin remodeling and the regulation of genome functioning. In this review, we outline the most recent and interesting findings on crop epigenetic responses to the environmental cues that are most relevant to climate change. In addition, we discuss a speculative point of view, in which we try to decipher the “epigenetic alphabet” that underlies crop adaptation mechanisms to climate change. The understanding of these mechanisms will pave the way to new strategies to design and implement the next generation of cultivars with a broad range of tolerance/resistance to stresses as well as balanced agronomic traits, with a limited loss of (epi)genetic variability.

Modulating the Inflammatory Response to Wounds and Cancer Through Infection

The zebrafish (Danio rerio) has recently emerged as an excellent model to study cancer biology and the tumour microenvironment, including the early inflammatory response to both wounding and early cancer growth. Here, we use high-resolution confocal imaging of translucent zebrafish larvae, with novel automated tracking and cell:cell interaction software, to investigate how innate immune cells behave and interact with repairing wounds and early cancer (pre-neoplastic) cells expressing a mutant active human oncogene (HRASG12V). We show that bacterial infections, delivered either systemically or locally, induce a change in the number and behaviour of neutrophils and macrophages recruited to acute wounds and to pre-neoplastic cells, and that infection can modify cellular interactions in ways that lead to a significant delay in wound healing and a reduction in the number of pre-neoplastic cells. Besides offering insights as to how Coley’s toxins and other cancer bacteriotherapies may function to reduce cancer burden, our study also highlights novel software tools that can be easily adapted to investigate cellular behaviours and interactions in other zebrafish models.

M, Shukla BN, Sharma M, Awasthi P, Mahtha SK, Yadav G, Laxmi A. Arabidopsis Target of Rapamycin Coordinates With Transcriptional and Epigenetic Machinery to Regulate Thermotolerance

Global warming exhibits profound effects on plant fitness and productivity. To withstand stress, plants sacrifice their growth and activate protective stress responses for ensuring survival. However, the switch between growth and stress is largely elusive. In the past decade, the role of the target of rapamycin (TOR) linking energy and stress signalling is emerging. Here, we have identified an important role of Glucose (Glc)-TOR signalling in plant adaptation to heat stress (HS). Glc via TOR governs the transcriptome reprogramming of a large number of genes involved in heat stress protection. Downstream to Glc-TOR, the E2Fa signalling module regulates the transcription of heat shock factors through direct recruitment of E2Fa onto their promoter regions. Also, Glc epigenetically regulates the transcription of core HS signalling genes in a TOR-dependent manner. TOR acts in concert with p300/CREB HISTONE ACETYLTRANSFERASE1 (HAC1) and dictates the epigenetic landscape of HS loci to regulate thermotolerance. Arabidopsis plants defective in TOR and HAC1 exhibited reduced thermotolerance with a decrease in the expression of core HS signalling genes. Together, our findings reveal a mechanistic framework in which Glc-TOR signalling through different modules integrates stress and energy signalling to regulate thermotolerance.

Genes and Mechanisms Involved in the Generation and Amplification of Basal Radial Glial Cells

The development of the cerebral cortex relies on different types of progenitor cell. Among them, the recently described basal radial glial cell (bRG) is suggested to be of critical importance for the development of the brain in gyrencephalic species. These cells are highly numerous in primate and ferret brains, compared to lissencephalic species such as the mouse in which they are few in number. Their somata are located in basal subventricular zones in gyrencephalic brains and they generally possess a basal process extending to the pial surface. They sometimes also have an apical process directed toward the ventricular surface, similar to apical radial glial cells (aRGs) from which they are derived, and whose somata are found more apically in the ventricular zone. bRGs share similarities with aRGs in terms of gene expression (SOX2, PAX6, and NESTIN), whilst also expressing a range of more specific genes (such as HOPX). In primate brains, bRGs can divide multiple times, self-renewing and/or generating intermediate progenitors and neurons. They display a highly specific cytokinesis behavior termed mitotic somal translocation. We focus here on recently identified molecular mechanisms associated with the generation and amplification of bRGs, including bRG-like cells in the rodent. These include signaling pathways such as the FGF-MAPK cascade, SHH, PTEN/AKT, PDGF pathways, and proteins such as INSM, GPSM2, ASPM, TRNP1, ARHGAP11B, PAX6, and HIF1α. A number of these proteins were identified through transcriptome comparisons in human aRGs vs. bRGs, and validated by modifying their activities or expression levels in the mouse. This latter experiment often revealed enhanced bRG-like cell production, even in some cases generating folds (gyri) on the surface of the mouse cortex. We compare the features of the identified cells and methods used to characterize them in each model. These important data converge to indicate pathways essential for the production and expansion of bRGs, which may help us understand cortical development in health and disease.

Insulin and Autophagy in Neurodegeneration

Crosstalk in the pathophysiological processes underpinning metabolic diseases and neurodegenerative disorders have been the subject of extensive investigation, in which insulin signaling and autophagy impairment demonstrate to be a common factor in both conditions. Although it is still somewhat conflicting, pharmacological and genetic strategies that regulate these pathways may be a promising approach for aggregate protein clearancing and consequently the delaying of onset or progression of the disease. However, as the response due to this modulation seems to be time-dependent, finding the right regulation of autophagy may be a potential target for drug development for neurodegenerative diseases. In this way, this review focuses on the role of insulin signaling/resistance and autophagy in some neurodegenerative diseases, discussing pharmacological and non-pharmacological interventions in these diseases.

Export Mechanisms and Energy Transduction in Type-III Secretion Machines

The remarkably complex architecture and organization of bacterial nanomachines originally raised the enigma to how they are assembled in a coordinated manner. Over the years, the assembly processes of the flagellum and evolutionary-related injectisome complexes have been deciphered and were shown to rely on a conserved protein secretion machine: the type-III secretion system. In this book chapter, we demonstrate how individually evolved mechanisms cooperate in highly versatile and robust secretion machinery to export and assemble the building blocks of those nanomachines.

Being a Neural Stem Cell: A Matter of Character But Defined by the Microenvironment

The cells that build the nervous system, either this is a small network of ganglia or a complicated primate brain, are called neural stem and progenitor cells. Even though the very primitive and the very recent neural stem cells (NSCs) share common basic characteristics that are hard-wired within their character, such as the expression of transcription factors of the SoxB family, their capacity to give rise to extremely different neural tissues depends significantly on instructions from the microenvironment. In this chapter we explore the nature of the NSC microenvironment, looking through evolution, embryonic development, maturity and even disease. Experimental work undertaken over the last 20 years has revealed exciting insight into the NSC microcosmos. NSCs are very capable in producing their own extracellular matrix and in regulating their behaviour in an autocrine and paracrine manner. Nevertheless, accumulating evidence indicates an important role for the vasculature, especially within the NSC niches of the postnatal brain; while novel results reveal direct links between the metabolic state of the organism and the function of NSCs.

Cellular Complexity in MAPK Signaling in Plants: Questions and Emerging Tools to Answer Them

Mitogen activated protein kinase (MAPK) cascades play an important role in many aspects of plant growth, development, and environmental response. Because of their central role in many important processes, MAPKs have been extensively studied using biochemical and genetic approaches. This work has allowed for the identification of the MAPK genes and proteins involved in a number of different signaling pathways. Less well developed, however, is our understanding of how MAPK cascades and their corresponding signaling pathways are organized at subcellular levels. In this review, we will provide an overview of plant MAPK signaling, including a discussion of what is known about cellular mechanisms for achieving signaling specificity. Then we will explore what is currently known about the subcellular localization of MAPK proteins in resting conditions and after pathway activation. Finally, we will discuss a number of new experimental methods that have not been widely deployed in plants that have the potential to provide a deeper understanding of the spatial and temporal dynamics of MAPK signaling.

Stress-induced changes in miRNA biogenesis and functioning

MicroRNAs (miRNAs) are small, noncoding RNAs that play key roles in the regulation of cellular homeostasis in eukaryotic organisms. There is emerging evidence that some of these processes are influenced by various forms of cellular stresses, including DNA damage, pathogen invasion or chronic stress associated with diseases. Many reports over the last decade demonstrate examples of stress-induced miRNA deregulation at the level of transcription, processing, subcellular localization and functioning. Moreover, core miRNA biogenesis proteins and their interactions with partners can be selectively regulated in response to stress signaling. However, little is known about the role of isomiRs and the interactions of miRNA with non-canonical targets in the context of the stress response. In this review, we summarize the current knowledge on miRNA functions under various stresses, including chronic stress and miRNA deregulation in the pathogenesis of age-associated neurodegenerative disorders.

TRAPPC13 modulates autophagy and the response to Golgi stress

Tether complexes play important roles in endocytic and exocytic trafficking of lipids and proteins. In yeast, the multisubunit transport protein particle (TRAPP) tether regulates endoplasmic reticulum (ER)-to-Golgi and intra-Golgi transport and is also implicated in autophagy. In addition, the TRAPP complex acts as a guanine nucleotide exchange factor (GEF) for Ypt1, which is homologous to human Rab1a and Rab1b. Here, we show that human TRAPPC13 and other TRAPP subunits are critically involved in the survival response to several Golgi-disrupting agents. Loss of TRAPPC13 partially preserves the secretory pathway and viability in response to brefeldin A, in a manner that is dependent on ARF1 and the large GEF GBF1, and concomitant with reduced caspase activation and ER stress marker induction. TRAPPC13 depletion reduces Rab1a and Rab1b activity, impairs autophagy and leads to increased infectivity to the pathogenic bacterium Shigella flexneri in response to brefeldin A. Thus, our results lend support for the existence of a mammalian TRAPPIII complex containing TRAPPC13, which is important for autophagic flux under certain stress conditions.