Actin Monoubiquitylation Is Induced in Plants in Response to Pathogens and Symbionts

Most dramatic examples of actin reorganization have been described during host-microbe interactions. Plasticity of actin is, in part, due to posttranslational modifications such as phosphorylation or ubiquitylation. Here, we show for the first time that actins found in root nodules of Phaseolus vulgaris are modified transiently during nodule development by monoubiquitylation. This finding was extended to root nodules of other legumes and to other plants infected with mycorrhiza or plant pathogens such as members of the genera Pseudomonas and Phytophthora. However, neither viral infections nor diverse stressful conditions (heat shock, wounding, or osmotic stress) induced this response. Additionally, this phenomenon was mimicked by the addition of a yeast elicitor or H2O2 to Phaseolus vulgaris suspension culture cells. This modification seems to provide increased stability of the microfilaments to proteolytic degradation and seems to be found in fractions in which the actin cytoskeleton is associated with membranes. All together, these data suggest that actin monoubiquitylation may be considered an effector mechanism of a general plant response against microbes.

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PvRACK1 Loss-of-Function Impairs Cell Expansion and Morphogenesis in Phaseolus vulgaris L. Root Nodules

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-11-10-0261 ◽

2011 ◽

Vol 24 (7) ◽

pp. 819-826 ◽

Cited By ~ 20

Author(s):

Tania Islas-Flores ◽

Gabriel Guillén ◽

Xóchitl Alvarado-Affantranger ◽

Miguel Lara-Flores ◽

Federico Sánchez ◽

...

Keyword(s):

Phaseolus Vulgaris ◽

Cell Expansion ◽

Root Nodules ◽

Microscopic Analysis ◽

Nodule Development ◽

Loss Of Function ◽

Rhizobium Tropici ◽

Transcript Accumulation ◽

Transgenic Roots ◽

Plant Signal Transduction

Receptor for activated C kinase (RACK1) is a highly conserved, eukaryotic protein of the WD-40 repeat family. Its peculiar β-propeller structure allows its interaction with multiple proteins in various plant signal-transduction pathways, including those arising from hormone responses, development, and environmental stress. During Phaseolus vulgaris root development, RACK1 (PvRACK1) mRNA expression was induced by auxins, abscissic acid, cytokinin, and gibberellic acid. In addition, during P. vulgaris nodule development, PvRACK1 mRNA was highly accumulated at 12 to 15 days postinoculation, suggesting an important role after nodule meristem initiation and Rhizobium nodule infection. PvRACK1 transcript accumulation was downregulated by a specific RNA interference construct which was expressed in transgenic roots of composite plants of P. vulgaris inoculated with Rhizobium tropici. PvRACK1 downregulated transcript levels were monitored by quantitative reverse-transcription polymerase chain reaction analysis in individual transgenic roots and nodules. We observed a clear phenotype in PvRACK1-knockdown nodules, in which nodule number and nodule cell expansion were impaired, resulting in altered nodule size. Microscopic analysis indicated that, in PvRACK1-knockdown nodules, infected and uninfected cells were considerably smaller (80 and 60%, respectively) than in control nodules. In addition, noninfected cells and symbiosomes in silenced nodules showed significant defects in membrane structure under electron microscopy analysis. These findings indicate that PvRACK1 has a pivotal role in cell expansion and in symbiosome and bacteroid integrity during nodule development.

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Perspectives on Remorin Proteins, Membrane Rafts, and Their Role During Plant–Microbe Interactions

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-07-10-0166 ◽

2011 ◽

Vol 24 (1) ◽

pp. 7-12 ◽

Cited By ~ 75

Author(s):

Iris K. Jarsch ◽

Thomas Ott

Keyword(s):

Current Knowledge ◽

Root Nodules ◽

Current Data ◽

Effector Proteins ◽

Host Cells ◽

Membrane Microdomains ◽

Membrane Rafts ◽

Microbe Interactions ◽

Host Microbe Interactions ◽

Molecular Patterns

Invasion of host cells by pathogenic or mutualistic microbes requires complex molecular dialogues that often determine host survival. Although several components of the underlying signaling cascades have recently been identified and characterized, our understanding of proteins that facilitate signal transduction or assemble signaling complexes is rather sparse. Our knowledge of plant-specific remorin proteins, annotated as proteins with unknown function, has recently advanced with respect to their involvement in host–microbe interactions. Current data demonstrating that a remorin protein restricts viral movement in tomato leaves and the importance of a symbiosis-specific remorin for bacterial infection of root nodules suggest that these proteins may serve such regulatory functions. Direct interactions of other remorins with a resistance protein in Arabidopsis thaliana, and differential phosphorylation upon perception of microbial-associated molecular patterns and during expression of bacterial effector proteins, strongly underline their roles in plant defense. Furthermore, the specific subcellular localization of remorins in plasma membrane microdomains now provides the opportunity to visualize membrane rafts in living plants cells. There, remorins may oligomerize and act as scaffold proteins during early signaling events. This review summarizes current knowledge of this protein family and the potential roles of remorins in membrane rafts.

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Detection of and Response to Signals Involved in Host-Microbe Interactions by Plant-Associated Bacteria

Microbiology and Molecular Biology Reviews ◽

10.1128/mmbr.69.1.155-194.2005 ◽

2005 ◽

Vol 69 (1) ◽

pp. 155-194 ◽

Cited By ~ 226

Author(s):

Anja Brencic ◽

Stephen C. Winans

Keyword(s):

Pseudomonas Syringae ◽

Plant Pathogens ◽

Root Nodules ◽

Complex Nature ◽

Natural Environments ◽

Associated Bacteria ◽

Bacterial Physiology ◽

The Family ◽

Microbe Interactions ◽

Host Detection

SUMMARY Diverse interactions between hosts and microbes are initiated by the detection of host-released chemical signals. Detection of these signals leads to altered patterns of gene expression that culminate in specific and adaptive changes in bacterial physiology that are required for these associations. This concept was first demonstrated for the members of the family Rhizobiaceae and was later found to apply to many other plant-associated bacteria as well as to microbes that colonize human and animal hosts. The family Rhizobiaceae includes various genera of rhizobia as well as species of Agrobacterium. Rhizobia are symbionts of legumes, which fix nitrogen within root nodules, while Agrobacterium tumefaciens is a pathogen that causes crown gall tumors on a wide variety of plants. The plant-released signals that are recognized by these bacteria are low-molecular-weight, diffusible molecules and are detected by the bacteria through specific receptor proteins. Similar phenomena are observed with other plant pathogens, including Pseudomonas syringae, Ralstonia solanacearum, and Erwinia spp., although here the signals and signal receptors are not as well defined. In some cases, nutritional conditions such as iron limitation or the lack of nitrogen sources seem to provide a significant cue. While much has been learned about the process of host detection over the past 20 years, our knowledge is far from being complete. The complex nature of the plant-microbe interactions makes it extremely challenging to gain a comprehensive picture of host detection in natural environments, and thus many signals and signal recognition systems remain to be described.

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Septins in Infections: Focus on Viruses

Pathogens ◽

10.3390/pathogens10030278 ◽

2021 ◽

Vol 10 (3) ◽

pp. 278

Author(s):

Thomas Henzi ◽

Nils Lannes ◽

Luis Filgueira

Keyword(s):

Influenza A ◽

Viral Infections ◽

Lateral Diffusion ◽

Human Herpesvirus ◽

Published Data ◽

Cellular Functions ◽

Microbe Interactions ◽

Host Microbe Interactions ◽

Microtubule Networks ◽

Cytoskeletal Elements

Human septins comprise a family of 13 genes that encode conserved GTP-binding proteins. They form nonpolar complexes, which assemble into higher-order structures, such as bundles, scaffolding structures, or rings. Septins are counted among the cytoskeletal elements. They interact with the actin and microtubule networks and can bind to membranes. Many cellular functions with septin participation have been described in the literature, including cytokinesis, motility, forming of scaffolding platforms or lateral diffusion barriers, vesicle transport, exocytosis, and recognition of micron-scale curvature. Septin dysfunction has been implicated in diverse human pathologies, including neurodegeneration and tumorigenesis. Moreover, septins are thought to affect the outcome of host–microbe interactions. Implication of septins has been demonstrated in fungal, bacterial, and viral infections. Knowledge on the precise function of a particular septin in the different steps of the virus infection and replication cycle is still limited. Published data for vaccinia virus (VACV), hepatitis C virus (HCV), influenza A virus (H1N1 and H5N1), human herpesvirus 8 (HHV-8), and Zika virus (ZIKV), all of major concern for public health, will be discussed here.

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Functional diversity of five homologous Cu+-ATPases present in Sinorhizobium meliloti

Microbiology ◽

10.1099/mic.0.079137-0 ◽

2014 ◽

Vol 160 (6) ◽

pp. 1237-1251 ◽

Cited By ~ 16

Author(s):

Sarju J. Patel ◽

Teresita Padilla-Benavides ◽

Jessica M. Collins ◽

José M. Argüello

Keyword(s):

Sinorhizobium Meliloti ◽

Nitrosative Stress ◽

Nodule Development ◽

Symbiotic Bacteria ◽

Redox Stress ◽

Free Living ◽

Mutant Strains ◽

Microbe Interactions ◽

Differential Gene ◽

Host Microbe Interactions

Copper is an important element in host–microbe interactions, acting both as a catalyst in enzymes and as a potential toxin. Cu+-ATPases drive cytoplasmic Cu+ efflux and protect bacteria against metal overload. Many pathogenic and symbiotic bacteria contain multiple Cu+-ATPase genes within particular genetic environments, suggesting alternative roles for each resulting protein. This hypothesis was tested by characterizing five homologous Cu+-ATPases present in the symbiotic organism Sinorhizobium meliloti. Mutation of each gene led to different phenotypes and abnormal nodule development in the alfalfa host. Distinct responses were detected in free-living S. meliloti mutant strains exposed to metal and redox stresses. Differential gene expression was detected under Cu+, oxygen or nitrosative stress. These observations suggest that CopA1a maintains the cytoplasmic Cu+ quota and its expression is controlled by Cu+ levels. CopA1b is also regulated by Cu+ concentrations and is required during symbiosis for bacteroid maturation. CopA2-like proteins, FixI1 and FixI2, are necessary for the assembly of two different cytochrome c oxidases at different stages of bacterial life. CopA3 is a phylogenetically distinct Cu+-ATPase that does not contribute to Cu+ tolerance. It is regulated by redox stress and required during symbiosis. We postulated a model where non-redundant homologous Cu+-ATPases, operating under distinct regulation, transport Cu+ to different target proteins.

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