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41.
Luis AJ Mur Amanda J Lloyd Simona M Cristescu Frans JM Harren Michael A Hall Aileen R Smith 《Plant signaling & behavior》2009,4(7):610-613
The hypersensitive response (HR) is a cell death phenomenon associated with localized resistance to pathogens. Biphasic patterns in the generation of H2O2, salicylic acid and ethylene have been observed in tobacco during the early stages of the HR. These biphasic models reflect an initial elicitation by pathogen-associated molecular patterns followed by a second phase, induced by pathogen-encoded avirulence gene products. The first phase has been proposed to potentiate the second, to increase the efficacy of plant resistance to disease. This potentiation is comparable to the “priming” of plant defenses which is seen when plants display systemic resistance to disease. The events regulating the generation of the biphasic wave, or priming, remains obscure, however recently we demonstrated a key role for nitric oxide in this process in a HR occurring in tobacco. Here we use laser photoacoustic detection to demonstrate that biphasic ethylene production also occurs during a HR occurring in Arabidopsis. We suggest that ethylene emanation during the HR represents a ready means of visualising biphasic events during the HR and that exploiting the genomic resources offered by this model species will facilitate the development of a mechanistic understanding of potentiating/priming processes.Key words: hypersensitive response, biphasic patterns, potentiation, defense priming, ethylene, ArabidopsisThe Hypersensitive Response (HR) is a cell death process which occurs at the site of attempted pathogen attack and which has been associated with host resistance.1 Much work on the regulation of the HR has indicated the importance of H2O2,2 and NO.3 A feature of H2O2 generation during the HR is its biphasic pattern (Fig. 1A). The first rise reflects elicitation by pathogen-associated molecular patterns (PAMPs)4 and the second reflects the interaction between a pathogen-encoded avirulence (avr) gene product with a plant resistance (R) gene. A key aspect of the first rise is the initiation of salicylic acid (SA) synthesis which potentiates the second rise and hence the potency of plant defense and the HR.5Open in a separate windowFigure 1Patterns of defense signal generation during the Pseudomonas syringae pv. phaseolicola elicited-hypersensitive response in tobacco (Nicotiana tabacum). Generation of (A) H2O2 (●, Mur18); (B) nitric oxide (◇; Mur12 (C) salicylic acid (SA, ■19) and (D) ethylene (○ Mur9) during a HR elicited by Pseudomonas syringae pv. phaseolicola (Psph) in tobacco cv. Samsun NN. In (A) a phase where SA acts to augment the second rise in H2O2—the potentiation phase—is highlighted. The potentiation phase is likely to be similar to defense “priming”.6 Methodological details are contained within the appropriate references. (E) A possible model for biphasic defense signal regulation during the Psph-elicited HR in tobacco. During an initial phase NO and H2O2 act to initiate SA biosynthesis, where SA and NO act to initiate a “H2O2 biphasic switch”. This could initially suppress both SA and the H2O2 generation but subsequently acts to potentiate a second phase of H2O2 generation. This in turn increases SA biosynthesis which could act with NO to initiate the “C2H4 biphasic switch” to potentiate ethylene production. These (and other) signals contribute to initiation of the HR and SAR.This potentiation mechanism appears to be similar to defense priming; when whole plants display systemic resistance to disease as opposed to a localized resistance against pathogens. Priming can be initiated (the “primary stimulus”) following attack with a necrotizing pathogen (leading to “systemic acquired resistance”, SAR) or non-pathogenic rhizosphere bacteria (to confer “induced systemic resistance”, ISR). In the primed state a plant stimulates a range of plant defense genes, produces anti-microbial phytoalexins and deposits cell wall strengthening molecules, but only on imposition of a “secondary stimulus”.6 Such secondary stimuli include SA3 or PAMPs7 and is likely to be mechanistically similar to the potentiation step in the biphasic pattern of H2O2 generation (shaded in Fig. 1A). Accordingly, the two phases in the biphasic wave represent primary and secondary stimuli in priming.Highlighting a similarity between local HR-based events and priming, adds further impetus to efforts aiming to describe the underlying mechanism(s), however both phenomena remain poorly understood. Besides SA, both jasmonates and abscisic acid (ABA) have been shown to prime defenses as have a range of non-plant chemicals, with β-aminobutyric acid (BABA) being perhaps most widely used.6,8 Mutants which fail to exhibit BABA-mediated potentiation were defective in either a cyclin-dependent kinase-like protein, a polyphosphoinositide phosphatase or an ABA biosynthetic enzyme.8We have recently investigated biphasic ethylene production during the HR in tobacco elicited by the nonhost HR-eliciting bacterial pathogen Pseudomonas syringae pv. phaseolicola.9 As with H2O2 generation, this pattern reflected PAMP-and AVR-dependent elicitation events and included a SA-mediated potentiation stage. Crucially, we also showed that NO was a vital component in the SA-potentiation mechanism. When this finding is integrated with our other measurements of defense signal generation in the same host-pathogen system the complexity in the signaling network is revealed (Fig. 1). NO generation (Fig. 1B) appeared to be coincident with the first rise in H2O2 (Fig. 1A) which initiated SA biosynthesis10,11 and together would contribute to the first small, but transient, rise in that hormone (Fig. 1C). In line with established models5 this momentary rise in SA coincides with the potentiation phase (shaded in Fig. 1A) required to augment the second rise in ROS. However, ethylene production seems to be correlated poorly with the patterns of NO, H2O2 and SA (Fig. 1D). Nevertheless, biphasic ethylene production was found to reflect PAMP and AVR-dependent recognition and included a SA-mediated potentiation step.9 Hence, ethylene production could be used as a post-hoc indicator of the potentiation mechanism. Therefore, our discovery that the second wave of ethylene production—a “biphasic switch”—is influenced by NO acting with SA could also be relevant to the H2O2 generation. Significantly, the second phases in both H2O2 and ethylene production occur exactly where SA and NO production coincides; in the case of H2O2 generation 2–4 h post challenge and with ethylene 6 h onwards (Fig. 1E).Thus, ethylene production represents a readily assayable marker to indicate perturbations in the underlying biphasic and possible priming mechanisms. As we have demonstrated, laser photoacoustic detection (LAPD) is a powerful on-line approach to determine in planta ethylene production in tobacco9,12 but any mechanistic investigations would be greatly facilitated if the genetic resources offered by the model species Arabidopsis could be exploited.To address this, Arabidopsis Col-0 rosettes were vacuum infiltrated with either Pseudomonas syringae pv. tomato (Pst) avrRpm1 (HR-eliciting), the virulent Pst strain and the non-HR eliciting and non-virulent Pst hrpA strain. Ethylene production was monitored by LAPD (Fig. 2A). Significantly, Pst avrRpm1 initiated a biphasic pattern of ethylene production whose kinetics were very similar to that seen in tobacco (compare Figs. 2A with with1D).1D). Inoculations with Pst and Pst hrpA only displayed the first PAMP-dependent rise in ethylene production. Thus, these data establish that Arabidopsis can be used to investigate biphasic switch mechanism(s) in ethylene production during the HR and possibly defense priming. When considering such mechanisms, it is relevant to highlight the work of Foschi et al.13 who observed that biphasic activation of a monomeric G protein to cause phase-specific activation of different kinase cascades. Interestingly, ethylene has been noted to initiate biphasic activation of G proteins and kinases in Arabidopsis, although differing in kinetics to the phases seen during the HR.14 Further, plant defense priming has been associated with the increased accumulation of MAP kinase protein.6Open in a separate windowFigure 2Ethylene in the Pseudomonas syringae pv. tomato elicited-hypersensitive response in Arabidopsis thaliana. (A) Ethylene production from 5 week old short day (8 h light 100 µmol.m2.sec−1) grown Arabidopsis rosette leaves which were vacuum infiltrated with bacterial suspensions (2 × 106 colony forming units.ml−1) of Pseudomonas syringae pv. tomato (Pst) strains detected using laser photoacoustic detection (LAPD). Experimental details of the ethylene detection by LAPD are detailed in Mur et al.9 The intercellular spaces in leaves were infiltrated with the HR-eliciting strain Pst avrRpm1, (■), the virulent strain Pst (△) or the non-virulent and non-HR eliciting derivative, Pst hrpA (◇). (B) The appearance of Arabidopsis Col-0 and etr1-1 leaves at various h following injection with 2 × 106 c.f.u.mL−1 with of Pst avrRpm1. (C) Explants (1 cm diameter discs) from Arabidopsis leaf areas infiltrated with suspensions of Pst avrRpm1 were placed in a 1.5 cm diameter well, bathed in 1 mL de-ionized H2O. Changes in the conductivity of the bathing solution, as an indicator of electrolyte leakage from either wild type Col-0 (◆), mutants which were compromised in ethylene signaling; etr1-1 (□), ein2-2 (▲) or which overproduced ethylene; eto2-1 (●) were measured using a conductivity meter. Methodological details are set out in Mur et al.9A further point requires consideration; the role of ethylene as a direct contributor to plant defense.15 The contribution of ethylene to the HR has been disputed,16 but in tobacco we have observed that altered ethylene production influenced the formation of a P. syringae pv. phaseolicola elicited HR.9 In Arabidopsis, cell death in the ethylene receptor mutant etr1-1 following inoculation with Pst avrRpm1 is delayed compared to wild type (Fig. 2B). When electrolyte leakage was used to quantify Pst avrRpm1 cell death, both etr1-1 and the ethylene insensitive signaling mutant ein2-1 exhibited slower death than wild-type but in the ethylene overproducing mutant eto2, cell death was augmented (Fig. 2C). These data indicate that ethylene influences the kinetics of the HR.Taking these data together we suggest that the complexity of signal interaction during the HR or in SAR/ISR could be further dissected by combining the genetic resources of Arabidopsis with measurements of ethylene production using such sensitive approaches as LAPD. 相似文献
42.
43.
As a result of low decomposition rates, high-latitude ecosystems store large amounts of carbon. Litter decomposition in these
ecosystems is constrained by harsh abiotic conditions, but also by the absence of macro-detritivores. We have studied the
potential effects of their climate change-driven northward range expansion on the decomposition of two contrasting subarctic
litter types. Litter of Alnus incana and Betula pubescens was incubated in microcosms together with monocultures and all possible combinations of three functionally different macro-detritivores
(the earthworm Lumbricus rubellus, isopod Oniscus asellus, and millipede Julus scandinavius). Our results show that these macro-detritivores stimulated decomposition, especially of the high-quality A. incana litter and that the macro-detritivores tested differed in their decomposition-stimulating effects, with earthworms having
the largest influence. Decomposition processes increased with increasing number of macro-detritivore species, and positive
net diveristy effects occurred in several macro-detritivore treatments. However, after correction for macro-detritivore biomass,
all interspecific differences in macro-detritivore effects, as well as the positive effects of species number on subarctic
litter decomposition disappeared. The net diversity effects also appeared to be driven by variation in biomass, with a possible
exception of net diversity effects in mass loss. Based on these results, we conclude that the expected climate change-induced
range expansion of macro-detritivores into subarctic regions is likely to result in accelerated decomposition rates. Our results
also indicate that the magnitude of macro-detritivore effects on subarctic decomposition will mainly depend on macro-detritivore
biomass, rather than on macro-detritivore species number or identity. 相似文献
44.
Alessia Cariani Miroslava Atanassova Dorte Bekkevold Gary R. Carvalho Montserrat Espiñeira Fabio Fiorentino Germana Garofalo Audrey J. Geffen Jakob. H. Hansen Sarah J. Helyar Einar E. Nielsen Rob Ogden Tomaso Patarnello Marco Stagioni FishPopTrace Consortium Fausto Tinti Luca Bargelloni 《Molecular ecology》2014,23(1):118-135
Shallow population structure is generally reported for most marine fish and explained as a consequence of high dispersal, connectivity and large population size. Targeted gene analyses and more recently genome‐wide studies have challenged such view, suggesting that adaptive divergence might occur even when neutral markers provide genetic homogeneity across populations. Here, 381 SNPs located in transcribed regions were used to assess large‐ and fine‐scale population structure in the European hake (Merluccius merluccius), a widely distributed demersal species of high priority for the European fishery. Analysis of 850 individuals from 19 locations across the entire distribution range showed evidence for several outlier loci, with significantly higher resolving power. While 299 putatively neutral SNPs confirmed the genetic break between basins (FCT = 0.016) and weak differentiation within basins, outlier loci revealed a dramatic divergence between Atlantic and Mediterranean populations (FCT range 0.275–0.705) and fine‐scale significant population structure. Outlier loci separated North Sea and Northern Portugal populations from all other Atlantic samples and revealed a strong differentiation among Western, Central and Eastern Mediterranean geographical samples. Significant correlation of allele frequencies at outlier loci with seawater surface temperature and salinity supported the hypothesis that populations might be adapted to local conditions. Such evidence highlights the importance of integrating information from neutral and adaptive evolutionary patterns towards a better assessment of genetic diversity. Accordingly, the generated outlier SNP data could be used for tackling illegal practices in hake fishing and commercialization as well as to develop explicit spatial models for defining management units and stock boundaries. 相似文献
45.
46.
47.
Is incest common in gray wolf packs? 总被引:3,自引:2,他引:1
Smith Deborah; Meier Thomas; Geffen Eli; Mech L. David; Burch John W.; Adams Layne G.; Wayne Robert K. 《Behavioral ecology》1997,8(4):384-391
Wolf packs generally consist of a breeding pair and their maturingoffspring that help provision and protect pack young. Becausethe reproductive tenure in wolves is often short, reproductivelymature offspring might replace their parents, resulting in siblingor parent-offspring matings. To determine the extent of incestuouspairings, we measured relatedness based on variability in 20microsatellite loci of mated pairs, parent-offspring pairs,and siblings in two populations of gray wolves. Our 16 sampledmated pairs had values of relatedness not overlapping thoseof known parent-offspring or sibling dyads, which is consistentwith their being unrelated or distantly related. These resultssuggest that full siblings or a parent and its offspring rarelymate and that incest avoidance is an important constraint ongray wolf behavioral ecology 相似文献
48.
49.
Nathan Geffen 《Developing world bioethics》2016,16(1):45-54
Drug‐resistant tuberculosis (TB) has a high mortality rate. Most medicines used to treat it are poorly tested and have terrible side effects. Activists have campaigned for patients with drug‐resistant TB to have access to experimental drugs, particularly one called bedaquiline, before these have been approved by regulatory authorities such as the Food and Drug Administration (FDA) in the United States (US) and the Medicines Control Council (MCC) in South Africa. Some activists have also campaigned for bedaquiline to be approved by regulatory authorities before testing of the drug is completed. These campaigns raise ethical concerns about whether patients should be offered experimental, unapproved, medicines for the treatment of life‐threatening illnesses, and if authorities should approve drugs for life‐threatening illnesses when vital questions about safety and efficacy remain outstanding. 相似文献
50.
Nucleotide sequence analysis of the lemur beta-globin gene family: evidence for major rate fluctuations in globin polypeptide evolution 总被引:1,自引:0,他引:1
Lemur beta-related globin genes have been isolated and sequenced. Orthology
of prosimian and human epsilon-, gamma-, and beta-related globin genes was
established by dot-matrix analysis. All of these lemur globin genes
potentially encode functional beta-related globin polypeptides, though
precisely when the gamma-globin gene is expressed remains unknown. The
organization of the 18-kb brown lemur beta-globin gene cluster (5'
epsilon-gamma-[psi eta-delta]-beta 3') is consistent with its evolution by
contraction via unequal crossing-over from the putative ancestral mammalian
beta-globin gene cluster (5' epsilon-gamma- eta-delta-beta 3'). The dwarf
lemur nonadult globin genes are arranged as in the brown lemur. Similar
levels of synonymous (silent) nucleotide substitutions and noncoding DNA
sequence differences have accumulated between species in all of these
genes, suggesting a uniform rate of noncoding DNA divergence throughout
primate beta-globin gene clusters. These differences are comparable with
those observed in the nonfunctional psi eta pseudogene and have therefore
accumulated at the presumably maximal neutral rate. In contrast,
nonsynonymous (replacement) nucleotide substitutions show a significant
heterogeneity in distribution for both the same gene in different lineages
and different genes in the same lineage. These major fluctuations in
replacement but not silent substitution rates cannot be attributed to
changes in mutation rate, suggesting that changes in the rate of globin
polypeptide evolution in primates is not governed solely by variable
mutation rates.
相似文献