The antimicrobial peptaibol trichokonin IV promotes plant growth and induces systemic resistance against Botrytis cinerea infection in moth orchid

Trichokonins (TKs) are antimicrobial peptaibols that are extracted from Trichoderma pseudokoningii strain SMF2. We discovered that TK VI, the primary active constituent of TKs, not only promotes growth, but also induces systemic resistance against grey mould caused by Botrytis cinerea in moth orchid (Phalaenopsis). Firstly, following treatment with TK VI, the growth of several varieties of Phalaenopsis increased relative to the control treatment. Both the aboveground and belowground biomass increased, particularly the length, superficial area, volume and root branching. Secondly, treatment with TK VI by either root or foliar application controlled grey mould on the moth orchids. Following irrigation with TK VI, the activities of defence‐related enzymes, including peroxidase, polyphenol oxidase and phenylalanine ammonia‐lyase, and the resistance‐related enzymes, including superoxide dismutase and catalase, all increased, while those of harmful substance malondialdehyde decreased. These findings indicated that induced systemic resistance was the primary mechanism of control.     

Structures and recognition modes of toll‐like receptors

Toll‐like receptors (TLRs) recognize common structural patterns in diverse microbial molecules and play central roles in the innate immune response. The structures of extracellular domains and their ligand complexes of several TLRs have been determined by X‐ray crystallography. Here, we discuss recent advances on structures and activation mechanisms of TLRs. Despite the differences in interaction areas of ligand with TLRs, the extracellular domains of TLRs all adopt horseshoe‐shaped structures and the overall M‐shape of the TLR–ligand complexes is strikingly similar. The structural rearrangement information of TLRs sheds new light on their ligand‐recognition and ‐activation mechanisms. Proteins 2016; 85:3–9. © 2016 Wiley Periodicals, Inc.     

Characterization,expression analysis and localization pattern of toll‐like receptor 1 (tlr1) and toll‐like receptor 2 (tlr2) genes in grass carp Ctenopharyngodon idella

In this study, the toll‐like receptor 1 (tlr1) and toll‐like receptor 2 (tlr2) genes of grass carp Ctenopharyngodon idella were cloned and characterized. tlr1 and tlr2 were found to be highly expressed in immune system organs such as spleen, middle kidney and heart kidney. The expression level of tlr1 and tlr2 was found to be up‐regulated at the later stage of viral challenge process. Moreover, subcellular localization indicated that Tlr1 and Tlr2 shared similar localization pattern and both of them may locate in the plasma membrane of transfected cells.     

Functional analysis of related CrRLK1L receptor‐like kinases in pollen tube reception

The Catharanthus roseus Receptor‐Like Kinase 1‐like (CrRLK1L) family of 17 receptor‐like kinases (RLKs) has been implicated in a variety of signaling pathways in Arabidopsis, ranging from pollen tube (PT) reception and tip growth to hormonal responses. The extracellular domains of these RLKs have malectin‐like domains predicted to bind carbohydrate moieties. Domain swap analysis showed that the extracellular domains of the three members analyzed (FER, ANX1, HERK1) are not interchangeable, suggesting distinct upstream components, such as ligands and/or co‐factors. In contrast, their intercellular domains are functionally equivalent for PT reception, indicating that they have common downstream targets in their signaling pathways. The kinase domain is necessary for FER function, but kinase activity itself is not, indicating that other kinases may be involved in signal transduction during PT reception.     

A pair of receptor‐like kinases is responsible for natural variation in shoot growth response to mannitol treatment in Arabidopsis thaliana

Growth is a complex trait that adapts to the prevailing conditions by integrating many internal and external signals. Understanding the molecular origin of this variation remains a challenging issue. In this study, natural variation of shoot growth under mannitol‐induced stress was analyzed by standard quantitative trait locus mapping methods in a recombinant inbred line population derived from a cross between the Col‐0 and Cvi‐0 Arabidopsis thaliana accessions. Cloning of a major QTL specific to mannitol‐induced stress condition led to identification of EGM1 and EGM2, a pair of tandem‐duplicated genes encoding receptor‐like kinases that are potentially involved in signaling of mannitol‐associated stress responses. Using various genetic approaches, we identified two non‐synonymous mutations in the EGM2[Cvi] allele that are shared by at least ten accessions from various origins and are probably responsible for a specific tolerance to mannitol. We have shown that the enhanced shoot growth phenotype contributed by the Cvi allele is not linked to generic osmotic properties but instead to a specific chemical property of mannitol itself. This result raises the question of the function of such a gene in A. thaliana, a species that does not synthesize mannitol. Our findings suggest that the receptor‐like kinases encoded by EGM genes may be activated by mannitol produced by pathogens such as fungi, and may contribute to plant defense responses whenever mannitol is present.     

Range position and climate sensitivity: The structure of among‐population demographic responses to climatic variation

Species’ distributions will respond to climate change based on the relationship between local demographic processes and climate and how this relationship varies based on range position. A rarely tested demographic prediction is that populations at the extremes of a species’ climate envelope (e.g., populations in areas with the highest mean annual temperature) will be most sensitive to local shifts in climate (i.e., warming). We tested this prediction using a dynamic species distribution model linking demographic rates to variation in temperature and precipitation for wood frogs (Lithobates sylvaticus) in North America. Using long‐term monitoring data from 746 populations in 27 study areas, we determined how climatic variation affected population growth rates and how these relationships varied with respect to long‐term climate. Some models supported the predicted pattern, with negative effects of extreme summer temperatures in hotter areas and positive effects on recruitment for summer water availability in drier areas. We also found evidence of interacting temperature and precipitation influencing population size, such as extreme heat having less of a negative effect in wetter areas. Other results were contrary to predictions, such as positive effects of summer water availability in wetter parts of the range and positive responses to winter warming especially in milder areas. In general, we found wood frogs were more sensitive to changes in temperature or temperature interacting with precipitation than to changes in precipitation alone. Our results suggest that sensitivity to changes in climate cannot be predicted simply by knowing locations within the species’ climate envelope. Many climate processes did not affect population growth rates in the predicted direction based on range position. Processes such as species‐interactions, local adaptation, and interactions with the physical landscape likely affect the responses we observed. Our work highlights the need to measure demographic responses to changing climate.     

Sinorhizobium meliloti succinylated high‐molecular‐weight succinoglycan and the Medicago truncatula LysM receptor‐like kinase MtLYK10 participate independently in symbiotic infection

The formation of nitrogen‐fixing nodules on legume hosts is a finely tuned process involving many components of both symbiotic partners. Production of the exopolysaccharide succinoglycan by the nitrogen‐fixing bacterium Sinorhizobium meliloti 1021 is needed for an effective symbiosis with Medicago spp., and the succinyl modification to this polysaccharide is critical. However, it is not known when succinoglycan intervenes in the symbiotic process, and it is not known whether the plant lysin‐motif receptor‐like kinase MtLYK10 intervenes in recognition of succinoglycan, as might be inferred from work on the Lotus japonicus MtLYK10 ortholog, LjEPR3. We studied the symbiotic infection phenotypes of S. meliloti mutants deficient in succinoglycan production or producing modified succinoglycan, in wild‐type Medicago truncatula plants and in Mtlyk10 mutant plants. On wild‐type plants, S. meliloti strains producing no succinoglycan or only unsuccinylated succinoglycan still induced nodule primordia and epidermal infections, but further progression of the symbiotic process was blocked. These S. meliloti mutants induced a more severe infection phenotype on Mtlyk10 mutant plants. Nodulation by succinoglycan‐defective strains was achieved by in trans rescue with a Nod factor‐deficient S. meliloti mutant. While the Nod factor‐deficient strain was always more abundant inside nodules, the succinoglycan‐deficient strain was more efficient than the strain producing only unsuccinylated succinoglycan. Together, these data show that succinylated succinoglycan is essential for infection thread formation in M. truncatula, and that MtLYK10 plays an important, but different role in this symbiotic process. These data also suggest that succinoglycan is more important than Nod factors for bacterial survival inside nodules.     

ZmSTK1 and ZmSTK2, encoding receptor‐like cytoplasmic kinase,are involved in maize pollen development with additive effect

Pollen germination and pollen tube growth are important physiological processes of sexual reproduction of plants and also are involved in signal transduction. Our previous study reveals that ZmSTK1 and ZmSTK2 are two receptor‐like cytoplasmic kinases (RLCK) homologs in Zea mays as members of receptor‐like protein kinase (RLK) subfamily, sharing 86% identity at the amino acid level. Here, we report that ZmSTK1 and ZmSTK2, expressed at late stages of pollen development, regulate maize pollen development with additive effect. ZmSTK1 or ZmSTK2 mutation exhibited severe pollen transmission deficiency, which thus influenced pollen fertility. Moreover, the kinase domains of ZmSTKs were cross‐interacted with C‐terminus of enolases detected by co‐immunoprecipitation (Co‐IP) and yeast two‐hybrid system (Y2H), respectively. Further, the detective ZmSTK1 or ZmSTK2 was associated with decreased activity of enolases and also reduced downstream metabolite contents, which enolases are involved in glycolytic pathway, such as phosphoenolpyruvate (PEP), pyruvate, ADP/ATP, starch, glucose, sucrose and fructose. This study reveals that ZmSTK1 and ZmSTK2 regulate maize pollen development and indirectly participate in glycolytic pathway.     

The Arabidopsis LecRK‐VI.2 associates with the pattern‐recognition receptor FLS2 and primes Nicotiana benthamiana pattern‐triggered immunity

Pattern‐triggered immunity (PTI) is broad spectrum and manipulation of PTI is believed to represent an attractive way to engineer plants with broad‐spectrum disease resistance. PTI is activated upon perception of microbe‐associated molecular patterns (MAMPs) by pattern‐recognition receptors (PRRs). We have recently demonstrated that the L‐type lectin receptor kinase‐VI.2 (LecRK‐VI.2) positively regulates Arabidopsis thaliana PTI. Here we show through in vitro pull‐down, bimolecular fluorescence complementation and co‐immunoprecipitation analyses that LecRK‐VI.2 associates with the PRR FLS2. We also demonstrated that LecRK‐VI.2 from the cruciferous plant Arabidopsis remains functional after interfamily transfer to the Solanaceous plant Nicotiana benthamiana. Wild tobacco plants ectopically expressing LecRK‐VI.2 were indeed more resistant to virulent hemi‐biotrophic and necrotrophic bacteria, but not to the fungal pathogen Botrytis cinerea suggesting that, as with Arabidopsis, the LecRK‐VI.2 protective effect in N. benthamiana is bacteria specific. Ectopic expression of LecRK‐VI.2 in N. benthamiana primed PTI‐mediated reactive oxygen species production, mitogen‐activated protein kinase (MAPK) activity, callose deposition and gene expression upon treatment with the MAMP flagellin. Our findings identified LecRK‐VI.2 as a member of the FLS2 receptor complex and suggest that heterologous expression of components of PRR complexes can be used as tools to engineer plant disease resistance to bacteria.     

Anther‐smut fungi from more contaminated sites in Chernobyl show lower infection ability and lower viability following experimental irradiation

The long‐term contamination that followed the nuclear disaster at Chernobyl provides a case study for the effects of chronic ionizing radiation on living organisms and on their ability to tolerate or evolve resistance to such radiation. Previously, we studied the fertility and viability of early developmental stages of a castrating plant pathogen, the anther‐smut fungus Microbotryum lychnidis‐dioicae, isolated from field sites varying over 700‐fold in degree of radioactive contamination. Neither the budding rate of haploid spores following meiosis nor the karyotype structure varied with increasing radiation levels at sampling sites. Here, we assessed the ability of the same M. lychnidis‐dioicae strains to perform their whole life cycle, up to the production of symptoms in the plants, that is, the development of anthers full of fungal spores; we also assessed their viability under experimental radiation. Fungal strains from more contaminated sites had no lower spore numbers in anthers or viability, but infected host plants less well, indicating lower overall fitness due to radioactivity exposure. These findings improve our understanding of the previous field data, in which the anther‐smut disease prevalence on Silene latifolia plants caused by M. lychnidis‐dioicae was lower at more contaminated sites. Although the fungus showed relatively high resistance to experimental radiation, we found no evidence that increased resistance to radiation has evolved in populations from contaminated sites. Fungal strains from more contaminated sites even tolerated or repaired damage from a brief acute exposure to γ radiation less well than those from non‐ or less contaminated sites. Our results more generally concur with previous studies in showing that the fitness of living organisms is affected by radiation after nuclear disasters, but that they do not rapidly evolve higher tolerance.     

The Brassica napus receptor‐like protein RLM2 is encoded by a second allele of the LepR3/Rlm2 blackleg resistance locus

Leucine‐rich repeat receptor‐like proteins (LRR‐RLPs) are highly adaptable parts of the signalling apparatus for extracellular detection of plant pathogens. Resistance to blackleg disease of Brassica spp. caused by Leptosphaeria maculans is largely governed by host race‐specific R‐genes, including the LRR‐RLP gene LepR3. The blackleg resistance gene Rlm2 was previously mapped to the same genetic interval as LepR3. In this study, the LepR3 locus of the Rlm2 Brassica napus line ‘Glacier DH24287’ was cloned, and B. napus transformants were analysed for recovery of the Rlm2 phenotype. Multiple B. napus, B. rapa and B. juncea lines were assessed for sequence variation at the locus. Rlm2 was found to be an allelic variant of the LepR3 LRR‐RLP locus, conveying race‐specific resistance to L. maculans isolates harbouring AvrLm2. Several defence‐related LRR‐RLPs have previously been shown to associate with the RLK SOBIR1 to facilitate defence signalling. Bimolecular fluorescence complementation (BiFC) and co‐immunoprecipitation of RLM2‐SOBIR1 studies revealed that RLM2 interacts with SOBIR1 of Arabidopsis thaliana when co‐expressed in Nicotiana benthamiana. The interaction of RLM2 with AtSOBIR1 is suggestive of a conserved defence signalling pathway between B. napus and its close relative A. thaliana.     

Inhibition of cytokine response to TLR stimulation and alleviation of collagen‐induced arthritis in mice by Schistosoma japonicum peptide SJMHE1

Helminth‐derived products have recently been shown to prevent the development of inflammatory diseases in mouse models. However, most identified immunomodulators from helminthes are mixtures or macromolecules with potentially immunogenic side effects. We previously identified an immunomodulatory peptide called SJMHE1 from the HSP60 protein of Schistosoma japonicum. In this study, we assessed the ability of SJMHE1 to affect murine splenocytes and human peripheral blood mononuclear cells (PBMCs) stimulated by toll‐like receptor (TLR) ligands in vitro and its treatment effect on mice with collagen‐induced arthritis (CIA). We show that SJMHE1 not only modulates the cytokine production of murine macrophage (MΦ) and dendritic cell but also affects cytokine production upon coculturing with allogeneic CD4⁺ T cell. SJMHE1 potently inhibits the cytokine response to TLR ligands lipopolysaccharide (LPS), CpG oligodeoxynucleotides (CpG) or resiquimod (R848) from mouse splenocytes, and human PBMCs stimulated by LPS. Furthermore, SJMHE1 suppressed clinical signs of CIA in mice and blocked joint erosion progression. This effect was mediated by downregulation of key cytokines involved in the pathogenesis of CIA, such as interferon‐γ (IFN‐γ), tumour necrosis factor‐α (TNF‐α), interleukin (IL)‐6, IL‐17, and IL‐22 and up‐regulation of the inhibitory cytokine IL‐10, Tgf‐β1 mRNA, and CD4⁺CD25⁺Foxp3⁺ Tregs. This study provides new evidence that the peptide from S. japonicum, which is the ‘safe’ selective generation of small molecule peptide that has evolved during host–parasite interactions, is of great value in the search for novel anti‐inflammatory agents and therapeutic targets for autoimmune diseases.