Inducible defense-related proteins have been described in many plant species upon infection with oomycetes, fungi, bacteria, or viruses, or insect attack. Several types of proteins are common and ...have been classified into 17 families of pathogenesis-related proteins (PRs). Others have so far been found to occur more specifically in some plant species. Most PRs and related proteins are induced through the action of the signaling compounds salicylic acid, jasmonic acid, or ethylene, and possess antimicrobial activities in vitro through hydrolytic activities on cell walls, contact toxicity, and perhaps an involvement in defense signaling. However, when expressed in transgenic plants, they reduce only a limited number of diseases, depending on the nature of the protein, plant species, and pathogen involved. As exemplified by the PR-1 proteins in Arabidopsis and rice, many homologous proteins belonging to the same family are regulated developmentally and may serve different functions in specific organs or tissues. Several defense-related proteins are induced during senescence, wounding or cold stress, and some possess antifreeze activity. Many defense-related proteins are present constitutively in floral tissues and a substantial number of PR-like proteins in pollen, fruits, and vegetables can provoke allergy in humans. The evolutionary conservation of similar defense-related proteins in monocots and dicots, but also their divergent occurrence in other conditions, suggest that these proteins serve essential functions in plant life, whether in defense or not.
Plants activate defence responses to protect themselves against microbial pathogens and herbivorous insects. However, induction of defences comes at a price, as the associated allocation costs, ...autotoxicity costs and ecological costs form fitness penalties. Upon pathogen or insect attack, resources are allocated to defences instead of to plant growth and reproduction, while above‐ and below‐ground interactions with beneficial organisms may also be disturbed. The phytohormones salicylic acid and jasmonic acid are major players in the regulation of induced defences and their associated fitness costs. Hormone‐controlled signalling pathways cross‐communicate, providing the plant with a finely tuned defence regulatory system that can contribute to a reduction of fitness costs by repressing ineffective defences. However, this sophisticated regulatory system causes ecological costs, because activated resistance to one organism can suppress resistance to another. Moreover, the system can be hijacked by invading organisms that manipulate it for their own benefit. Priming for enhanced defence emerged as a defence mechanism with limited fitness costs. Because priming results in a faster and stronger activation of defence only after pathogen or insect attack, the limited costs of the primed state are often outweighed by the benefits in environments with pathogen or herbivore pressure. The balance between protection and fitness is crucial for a plant's success and is therefore of great interest for plant breeders and farmers. By combining molecular knowledge and ecological relevance of defence mechanisms, one can gain fundamental insight into how and why plants integrate different immune signals to cope with their natural multitrophic environment in a cost‐effective manner.
Systemic resistance induced by rhizosphere bacteria Loon, L.C. van (Utrecht University, Utrecht, The Netherlands.); Bakker, P.A.H.M; Pieterse, C.M.J
Annual review of phytopathology,
01/1998, Letnik:
36, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Nonpathogenic rhizobacteria can induce a systemic resistance in plants that is phenotypically similar to pathogen-induced systemic acquired resistance (SAR). Rhizobacteria-mediated induced systemic ...resistance (ISR) has been demonstrated against fungi, bacteria, and viruses in Arabidopsis, bean, carnation, cucumber, radish, tobacco, and tomato under conditions in which the inducing bacteria and the challenging pathogen remained spatially separated. Bacterial strains differ in their ability to induce resistance in different plant species, and plants show variation in the expression of ISR upon induction by specific bacterial strains. Bacterial determinants of ISR include lipopolysaccharides, siderophores, and salicylic acid (SA). Whereas some of the rhizobacteria induce resistance through the SA-dependent SAR pathway, others do not and require jasmonic acid and ethylene perception by the plant for ISR to develop. No consistent host plant alterations are associated with the induced state, but upon challenge inoculation, resistance responses are accelerated and enhanced. ISR is effective under field conditions and offers a natural mechanism for biological control of plant disease.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Colonisation of plant roots by selected beneficial Trichoderma fungi or Pseudomonas bacteria can result in the activation of a systemic defence response that is effective against a broad spectrum of ...pathogens. In Arabidopsis thaliana, induced systemic resistance (ISR) triggered by the rhizobacterial strain Pseudomonas fluorescens WCS417r is regulated by a jasmonic acid- and ethylene-dependent defence signalling pathway. Jasmonic acid and ethylene also play a role in Trichoderma-induced resistance. To further investigate the similarities between rhizobacteria- and Trichoderma-induced resistance, we studied the response of Arabidopsis to root colonisation by Trichoderma asperellum T34. In many aspects T34-ISR was similar to WCS417r-ISR. First, colonisation of the roots by T34 rendered the leaves more resistant to the bacterial pathogen Pseudomonas syringae pv. tomato, the biotrophic oomycete Hyaloperonospora parasitica and the necrotrophic fungus Plectosphaerella cucumerina. Second, treatment of the roots with T34 primed the leaf tissue for enhanced jasmonic acid-responsive gene expression and increased formation of callose-containing papillae upon pathogen attack. Third, T34-ISR was fully expressed in the salicylic acid impaired mutant sid2, but blocked in the defence regulatory mutant npr1. Finally, we show that the root-specific transcription factor MYB72, which is essential in early signalling steps of WCS417r-ISR, is also required for T34-ISR. Together, these results indicate that the defence pathways triggered by beneficial Trichoderma and Pseudomonas spp. strains are highly similar and that MYB72 functions as an early node of convergence in the signalling pathways that are induced by these different beneficial microorganisms.
Abstract
One century after the first report of Dutch elm disease (DED), there is still no practical solution for this problem threatening European and American elms (Ulmus spp.). The long breeding ...cycles needed to select resistant genotypes and the lack of efficient treatments keep disease incidence at high levels. In this work, the expression of defense-related genes to the causal agent of DED, Ophiostoma novo-ulmi Brasier, was analyzed in in vitro clonal plantlets from two DED-resistant and two DED-susceptible Ulmus minor Mill. trees. In addition, the effect of the inoculation of an endophytic pink-pigmented yeast (Cystobasidium sp.) on the plant’s defense system was tested both individually and in combination with O. novo-ulmi. The multifactorial nature of the resistance to DED was confirmed, as no common molecular response was found in the two resistant genotypes. However, the in vitro experimental system allowed discrimination of the susceptible from the resistant genotypes, showing higher levels of oxidative damage and phenolic compounds in the susceptible genotypes after pathogen inoculation. Inoculation of the endophyte before O. novo-ulmi attenuated the plant molecular response induced by the pathogen and moderated oxidative stress levels. Niche competition, endophyte–pathogen antagonism and molecular crosstalk between the host and the endophyte are discussed as possible mechanisms of stress reduction. In sum, our results confirm the complex and heterogeneous nature of DED resistance mechanisms and highlight the possibility of using certain endophytic yeasts as biological tools to improve tree resilience against biotic stress.
WRKY proteins are transcription factors involved in many plant processes including plant responses to pathogens. Here, the cross activity of TaWRKY78 from the monocot wheat and AtWRKY20 from the ...dicot Arabidopsis on the cognate promoters of the orthologous PR4-type genes wPR4e and AtHEL of wheat and Arabidopsis, respectively, was investigated. In vitro analysis showed the ability of TaWRKY78 to bind a -17/+80 region of the wPR4e promoter, containing one cis-acting W-box. Moreover, transient expression analysis performed on both TaWRKY78 and AtWRKY20 showed their ability to recognize the cognate cis-acting elements present in the wPR4e and AtHEL promoters, respectively. Finally, this paper provides evidence that both transcription factors are able to cross-regulate the orthologous PR4 genes with an efficiency slightly lower than that exerted on the cognate promoters. The observation that orthologous genes are subjected to similar transcriptional control by orthologous transcription factors demonstrates that the terminal stages of signal transduction pathways leading to defence are conserved and suggests a fundamental role of PR4 genes in plant defence. Moreover, these results corroborate the hypothesis that gene orthology imply similar gene function and that diversification between monocot and dicot has most likely occurred after the specialization of WRKY function.
The plant hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) are major players in the regulation of signaling networks that are involved in induced defense responses against ...pathogens and insects. During the past two years, significant progress has been made in understanding the function of NON-EXPRESSOR OF PATHOGENESIS-RELATED GENES1 (NPR1), a key regulator of systemic acquired resistance (SAR), that is essential for transducing the SA signal to activate
PATHOGENESIS-RELATED (
PR) gene expression. SA-mediated redox changes in
Arabidopsis cells regulate both the functioning of NPR1 and its binding to TGA1, a member of the TGA family of transcription factors that activate SA-responsive elements in the promoters of
PR genes upon binding with NPR1. Apart from its role in regulating SAR in the nucleus, a novel cytosolic function of NPR1 in cross-communication between SA- and JA-dependent defense signaling pathways has been identified. Other advances in induced resistance signaling, such as the implication that ET is involved in the generation of systemic signal molecules, the suggestion of the involvement of lipid-derived molecules in long-distance signaling, and the identification of new components of various systemic defense signaling pathways, shed new light on how plants actively defend themselves against harmful organisms.
The purpose of this article is to debate the relationship between a convergent approach to the sciences and Scriptural authority. The thesis is that a multi-disciplinary convergent methodology may be ...beneficial in the current apologetical debate about the relevance of Scripture. This line of thought is also in compliance with the ideals of the protestant reformation. We will assess this view by investigating the possible consonance between scientific perspectives and theological confessions of what it means to be human. Subsequently the focus will shift to the impact consonance might have on the different interpretations of the creation narratives in Genesis. In conclusion, we will state the case for a convergent approach to the sciences, and the benefits with regard to Scriptural authority.Intradisciplinary and/or interdisciplinary implications: This study would not have been possible without extensive intradisciplinary and interdisciplinary research. The subject matter imposes on the researcher the necessity to make use of knowledge from across the theological spectrum. It compels the various subjects within the theological encyclopedia to take note of any new research and incorporate it. In addition, it dispels the myth that natural science and theology have little in common. From a holistic perspective on creation the need for continuous interaction between the sciences is imperative.
The purpose of this article is to prove through theological reasoning why consonance between the sciences is biblically, as well as confessional sound. The substance for the argument is found in the ...Biblical confessions regarding Christ, as well as God’s Trinitarian agency in the cosmos. The insight that Christ is God incarnated, the King, Creator and Redeemer of the entire cosmos, have important implications for the current dialogue between the sciences. An analysis of the relevant texts and historical confessions should prove that nothing in creation, including scientific endeavour, could be excluded from Christ’s interaction with creation. The Cosmological Christ is the Scriptural and confessional focal point for dialogue and consonance between the sciences.
To characterize the changes occurring in choroidal thickness (ChT) across the posterior pole during accommodation using enhanced-depth imaging optical coherence tomography (OCT).
Forty participants ...(mean age 21 ± 2 years) had measures of ChT and ocular biometry taken during accommodation to 0, 3, and 6 diopter (D) stimuli, with the Spectralis OCT and Lenstar biometer. A Badal optometer and cold mirror system was mounted on both instruments, allowing measurement collection while subjects viewed an external fixation target at varying accommodative demands.
The choroid exhibited significant thinning during accommodation to the 6 D stimulus in both subfoveal (mean change, -5 ± 7 μm) and parafoveal regions (P < 0.001). The magnitude of these changes varied by parafoveal meridian, with the largest changes seen in the temporal (-9 ± 12 μm) and inferotemporal (-8 ± 8 μm) meridians (P < 0.001). Axial length increased with accommodation (mean change, +5 ± 11 μm at 3 D, +14 ± 13 μm at 6 D), and these changes were weakly negatively associated with the choroidal changes (r2 = 0.114, P < 0.05).
A small, but significant thinning of the choroid was observed at the 6 D accommodation demand, which was greatest in the temporal and inferotemporal parafoveal choroid, and increased with increasing eccentricity from the fovea. The regional variation in the parafoveal thinning corresponds to the distribution of the nonvascular smooth muscle within the uvea, which may implicate these cells as the potential mechanism by which the choroid thins during accommodation.
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