Jasmonates and related oxylipins in plant responses to pathogenesis and herbivory.

The vigorous production of oxygenated fatty acids (oxylipins) is a characteristic response to pathogenesis and herbivory, and is often accompanied by the substantial release of small and reactive lipid-fragmentation products. Some oxylipins, most notably those of the jasmonate family, have key roles as potent regulators. Recent advances have been made in understanding oxylipin-regulated signal transduction in response to attack. Much jasmonate signaling takes place via a genetically defined signal network that is linked to the ethylene, auxin, and salicylic acid signal pathways, but a second aspect of jasmonate signaling is emerging. Some jasmonates and several newly discovered cyclopentenone lipids can activate or repress gene expression through the activities of a conserved electrophilic atom group.

Latitudinal patterns in plant defense: evolution of cardenolides, their toxicity and induction following herbivory.

Attempts over the past 50 years to explain variation in the abundance, distribution and diversity of plant secondary compounds gave rise to theories of plant defense. Remarkably, few phylogenetically robust tests of these long-standing theories have been conducted. Using >50 species of milkweed (Asclepias spp.), we show that variation among plant species in the induction of toxic cardenolides is explained by latitude, with higher inducibility evolving more frequently at lower latitudes. We also found that: (1) the production of cardenolides showed positive-correlated evolution with the diversity of cardenolides, (2) greater cardenolide investment by a species is accompanied by an increase in an estimate of toxicity (measured as chemical polarity) and (3) instead of trading off, constitutive and induced cardenolides were positively correlated. Analyses of root and shoot cardenolides showed concordant patterns. Thus, milkweed species from lower latitudes are better defended with higher inducibility, greater diversity and added toxicity of cardenolides.

Active transport of proton and calcium in higher plant cells.

Membrane transport of proton and calcium (Ca2+) plays a fundamental role in growth and developmental processes in higher plant cells. The plasma membrane contains an ATPase (P-ATPase) that pumps protons into the extracellular space, whereas two proton pumps, a vacuolar-type ATPase (V-ATPase) and a pyrophosphatase (H+-PPase) are associated with the tonoplast and pump protons into the vacuole. The P-ATPase, V-ATPase and H+-PPase catalyse electrogenic H+-translocation, giving rise to a proton motive force used to transport different molecules, via specific transport proteins (channels or carriers: H+-symport or H+-antiport), across the plasma membrane and the tonoplast

Phylogenetic plant community structure along elevation is lineage specific

The trend of closely related taxa to retain similar environmental preferences mediated by inherited traits suggests that several patterns observed at the community scale originate from longer evolutionary processes. While the effects of phylogenetic relatedness have been previously studied within a single genus or family, lineage-specific effects on the ecological processes governing community assembly have rarely been studied for entire communities or flora. Here, we measured how community phylogenetic structure varies across a wide elevation gradient for plant lineages represented by thirty-five families, using a co-occurrence index and net relatedness index (NRI). We propose a framework that analyses each lineage separately and reveals the trend of ecological assembly at tree nodes. We found prevailing phylogenetic clustering for more ancient nodes and overdispersion in more recent tree nodes. Closely related species may thus rapidly evolve new environmental tolerances to radiate into distinct communities, while older lineages likely retain inherent environmental tolerances to occupy communities in similar environments, either through efficient dispersal mechanisms or the exclusion of older lineages with more divergent environmental tolerances. Our study illustrates the importance of disentangling the patterns of community assembly among lineages to better interpret the ecological role of traits. It also sheds light on studies reporting absence of phylogenetic signal, and opens new perspectives on the analysis of niche and trait conservatism across lineages.

Toxic cardenolides: chemical ecology and coevolution of specialized plant-herbivore interactions.

CONTENTS: Summary 28 I. Historic background and introduction 29 II. Diversity of cardenolide forms 29 III. Biosynthesis 30 IV. Cardenolide variation among plant parts 31 V. Phylogenetic distribution of cardenolides 32 VI. Geographic distribution of cardenolides 34 VII. Ecological genetics of cardenolide production 34 VIII. Environmental regulation of cardenolide production 34 IX. Biotic induction of cardenolides 36 X. Mode of action and toxicity of cardenolides 38 XI. Direct and indirect effects of cardenolides on specialist and generalist insect herbivores 39 XII. Cardenolides and insect oviposition 39 XIII. Target site insensitivity 40 XIV. Alternative mechanisms of cardenolide resistance 40 XV. Cardenolide sequestration 41 Acknowledgements 42 References 42 SUMMARY: Cardenolides are remarkable steroidal toxins that have become model systems, critical in the development of theories for chemical ecology and coevolution. Because cardenolides inhibit the ubiquitous and essential animal enzyme Na(+) /K(+) -ATPase, most insects that feed on cardenolide-containing plants are highly specialized. With a huge diversity of chemical forms, these secondary metabolites are sporadically distributed across 12 botanical families, but dominate the Apocynaceae where they are found in > 30 genera. Studies over the past decade have demonstrated patterns in the distribution of cardenolides among plant organs, including all tissue types, and across broad geographic gradients within and across species. Cardenolide production has a genetic basis and is subject to natural selection by herbivores. In addition, there is strong evidence for phenotypic plasticity, with the biotic and abiotic environment predictably impacting cardenolide production. Mounting evidence indicates a high degree of specificity in herbivore-induced cardenolides in Asclepias. While herbivores of cardenolide-containing plants often sequester the toxins, are aposematic, and possess several physiological adaptations (including target site insensitivity), there is strong evidence that these specialists are nonetheless negatively impacted by cardenolides. While reviewing both the mechanisms and evolutionary ecology of cardenolide-mediated interactions, we advance novel hypotheses and suggest directions for future work.

The Roundtable on Sustainable Biofuels: plant scientist input needed.

The Energy Center at the Ecole Polytechnique Fédérale de Lausanne (Swiss federal institute of technology) is coordinating a multi-stakeholder effort, the Roundtable on Sustainable Biofuels (http://energycenter.epfl.ch/biofuels), to develop global standards for sustainable biofuels production and processing. Given that many of the aspects related to biofuel production request a high scientific level of understanding, it is crucial that scientists take part in the discussion.

Keratouveitis caused by sap of Euphorbia myrsinites plant.

BACKGROUND: Euphorbia plants grow in many gardens. Their milky latex is, however, a strong irritant which may induce various ocular lesions from keratoconjunctivitis to severe uveitis. HISTORY AND SIGNS: A 86-year-old woman developed a unilateral severe anterior chamber inflammation associated with descemtic folds after direct contact with sap of Euphorbia. Visual acuity was limited to counting fingers. Her eye was operated from filtering surgery ten years previously. The patient was closely followed to rule out the diagnosis of bacterial endophthalmitis. THERAPY AND OUTCOME: Symptoms progressively resolved after topical administration of 3 mg/mL ofloxacine and 1 % prednisolone acetate. CONCLUSIONS: Euphorbia sap toxicity may take different forms from keratoconjunctivitis to severe uveitis. Euphorbia sap-induced uveitis should be kept in mind when the patient has seen in contact with freshly cut plants.

Is the ability of biocontrol fluorescent pseudomonads to produce the antifungal metabolite 2,4-diacetylphloroglucinol really synonymous with higher plant protection?

The antifungal compound 2,4-diacetylphloroglucinol (Phl) contributes to biocontrol in pseudomonads, but whether or not Phl(+) biocontrol pseudomonads display higher plant-protecting activity than Phl(-) biocontrol pseudomonads remains to be demonstrated. This issue was addressed by assessing 230 biocontrol fluorescent pseudomonads selected from a collection of 3132 bacterial isolates obtained from 63 soils worldwide. One-third of the biocontrol pseudomonads were Phl(+) and almost all Phl(+) isolates also produced hydrogen cyanide (HCN). The only Phl(+) HCN(-) strain did harbor hcn genes, but with the deletion of a 134 bp hcnC fragment corresponding to an ADP-binding motif. Statistical analysis of biocontrol isolate distributions indicated that Phl production ability was associated with superior disease suppression activity in the Pythium-cucumber and Fusarium-tomato pathosystems, but this was also the case with HCN production ability. However, HCN significance was not as strong, as indicated both by the comparison of Phl(-) HCN(+) and Phl(-) HCN(-) strains and by correlation analyses. This is the first population-level demonstration of the higher plant-protecting activity of Phl(+) biocontrol pseudomonads in comparison with Phl(-) biocontrol pseudomonads.

Predicting spatial patterns of plant species richness: a comparison of direct macroecological and species stacking approaches

Aim This study compares the direct, macroecological approach (MEM) for modelling species richness (SR) with the more recent approach of stacking predictions from individual species distributions (S-SDM). We implemented both approaches on the same dataset and discuss their respective theoretical assumptions, strengths and drawbacks. We also tested how both approaches performed in reproducing observed patterns of SR along an elevational gradient.Location Two study areas in the Alps of Switzerland.Methods We implemented MEM by relating the species counts to environmental predictors with statistical models, assuming a Poisson distribution. S-SDM was implemented by modelling each species distribution individually and then stacking the obtained prediction maps in three different ways - summing binary predictions, summing random draws of binomial trials and summing predicted probabilities - to obtain a final species count.Results The direct MEM approach yields nearly unbiased predictions centred around the observed mean values, but with a lower correlation between predictions and observations, than that achieved by the S-SDM approaches. This method also cannot provide any information on species identity and, thus, community composition. It does, however, accurately reproduce the hump-shaped pattern of SR observed along the elevational gradient. The S-SDM approach summing binary maps can predict individual species and thus communities, but tends to overpredict SR. The two other S-SDM approaches the summed binomial trials based on predicted probabilities and summed predicted probabilities - do not overpredict richness, but they predict many competing end points of assembly or they lose the individual species predictions, respectively. Furthermore, all S-SDM approaches fail to appropriately reproduce the observed hump-shaped patterns of SR along the elevational gradient.Main conclusions Macroecological approach and S-SDM have complementary strengths. We suggest that both could be used in combination to obtain better SR predictions by following the suggestion of constraining S-SDM by MEM predictions.

Plant defense in the absence of jasmonic acid: the role of cyclopentenones.

The Arabidopsis opr3 mutant is defective in the isoform of 12-oxo-phytodienoate (OPDA) reductase required for jasmonic acid (JA) biosynthesis. Oxylipin signatures of wounded opr3 leaves revealed the absence of detectable 3R,7S-JA as well as altered levels of its cyclopentenone precursors OPDA and dinor OPDA. In contrast to JA-insensitive coi1 plants and to the fad3 fad7 fad8 mutant lacking the fatty acid precursors of JA synthesis, opr3 plants exhibited strong resistance to the dipteran Bradysia impatiens and the fungus Alternaria brassicicola. Analysis of transcript profiles in opr3 showed the wound induction of genes previously known to be JA-dependent, suggesting that cyclopentenones could fulfill some JA roles in vivo. Treating opr3 plants with exogenous OPDA powerfully up-regulated several genes and disclosed two distinct downstream signal pathways, one through COI1, the other via an electrophile effect of the cyclopentenones. We conclude that the jasmonate family cyclopentenone OPDA (most likely together with dinor OPDA) regulates gene expression in concert with JA to fine-tune the expression of defense genes. More generally, resistance to insect and fungal attack can be observed in the absence of JA.

Enhanced production of indole-3-acetic acid by a genetically modified strain of Pseudomonas fluorescens CHA0 affects root growth of cucumber but does not improve protection of the plant against Pythium root rot

The biocontrol strain CHA0 of Pseudomonas fluorescens produces small amounts of indole-3-acetic acid via the tryptophan side chain oxidase and the tryptophan transaminase pathways. A recombinant plasmid (pME3468) expressing the tryptophan monooxygenase pathway was introduced into strain CHA0; this resulted in elevated synthesis of indole-3-acetic acid in vitro, especially after addition of -tryptophan. In natural soil, strain CHA0/pME3468 increased fresh root weight of cucumber by 17-36%, compared to the effect of strain CHA0; root colonization was about 106 cells per g of root. However, both strains gave similar protection of cucumber against Pythium ultimum. In autoclaved soil, at 6×107 cells per g of root, strain CHA0 stimulated growth of roots and shoots, whereas strain CHA0/pME3468 caused root stunting and strong reduction of plant weight. These results are in agreement with the known effects of exogenous indole-3-acetic acid on plant roots and suggest that in the system examined, indole-3-acetic acid does not contribute to the biocontrol properties of strain CHA0.

DNA microarrays and plant defence

Recent progress in understanding plant defence has highlighted a complex, interacting network of signalling pathways leading to the induction of numerous genes. The advent of new technologies for the global analysis of gene expression is fundamentally affecting research in biology, and studies on plant defence should benefit from these new approaches. Genome-wide microarrays will provide a powerful tool for the discovery of all defence-related genes and should help in elucidating their function. The association of a particular signalling pathway with a defence response can be tested with microarrays and defined mutants. Comparison of transcript profiles after biotic and abiotic stresses reveals overlapping activation of defence-related genes and defines new concepts on how plants cope with multiple aggressions. The combination of expression data with other biochemical or metabolite measurements seems another promising approach. Finally, small-scale, dedicated microarrays containing sets of well-characterised genes might prove to be a very useful complement to more expensive, less accessible, large-scale arrays.

A quantitative genetic signature of senescence in a short-lived perennial plant.

The evolution of senescence (the physiological decline of organisms with age) poses an apparent paradox because it represents a failure of natural selection to increase the survival and reproductive performance of organisms. The paradox can be resolved if natural selection becomes less effective with age, because the death of postreproductive individuals should have diminished effects on Darwinian fitness [1, 2]. A substantial body of empirical work is consistent with this prediction for animals, which transmit their genes to progeny via an immortal germline. However, such evidence is still lacking in plants, which lack a germline and whose reproduction is diffuse and modular across the soma. Here, we provide experimental evidence for a genetic basis of senescence in the short-lived perennial plant Silene latifolia. Our pedigree-based analysis revealed a marked increase with age in the additive genetic variance of traits closely associated with fitness. This result thus extends to plants the quantitative genetic support for the evolutionary theory of senescence.

Genetic evidence that the higher plant Rab-D1 and Rab-D2 GTPases exhibit distinct but overlapping interactions in the early secretory pathway.

GTPases of the Rab1 subclass are essential for membrane traffic between the endoplasmic reticulum (ER) and Golgi complex in animals, fungi and plants. Rab1-related proteins in higher plants are unusual because sequence comparisons divide them into two putative subclasses, Rab-D1 and Rab-D2, that are conserved in monocots and dicots. We tested the hypothesis that the Rab-D1 and Rab-D2 proteins of Arabidopsis represent functionally distinct groups. RAB-D1 and RAB-D2a each targeted fluorescent proteins to the same punctate structures associated with the Golgi stacks and trans-Golgi-network. Dominant-inhibitory N121I mutants of each protein inhibited traffic of diverse cargo proteins at the ER but they appeared to act via distinct biochemical pathways as biosynthetic traffic in cells expressing either of the N121I mutants could be restored by coexpressing the wild-type form of the same subclass but not the other subclass. The same interaction was observed in transgenic seedlings expressing RAB-D1 [N121I]. Insertional mutants confirmed that the three Arabidopsis Rab-D2 genes were extensively redundant and collectively performed an essential function that could not be provided by RAB-D1, which was non-essential. However, plants lacking RAB-D1, RAB-D2b and RAB-D2c were short and bushy with low fertility, indicating that the Rab-D1 and Rab-D2 subclasses have overlapping functions.