Fungal Infection Reduces Herbivore-Induced Plant Volatiles of Maize but does not Affect Naïve Parasitoids

Plants attacked by insects release volatile compounds that attract the herbivores' natural enemies. This so-called indirect defense is plastic and may be affected by an array of biotic and abiotic factors. We investigated the effect of fungal infection as a biotic stress agent on the emission of herbivore-induced volatiles and the possible consequences for the attraction of two parasitoid species. Maize seedlings that were simultaneously attacked by the fungus Setosphaeria turcica and larvae of Spodoptera littoralis emitted a blend of volatiles that was qualitatively similar to the blend emitted by maize that was damaged by only the herbivore, but there was a clear quantitative difference. When simultaneously challenged by fungus and herbivore, the maize plants emitted in total 47% less of the volatiles. Emissions of green leaf volatiles were unaffected. In a six-arm olfactometer, the parasitoids Cotesia marginiventris and Microplitis rufiventris responded equally well to odors of herbivore-damaged and fungus- and herbivore-damaged maize plants. Healthy and fungus-infected plants were not attractive. An additional experiment showed that the performance of S. littoralis caterpillars was not affected by the presence of the pathogen, nor was there an effect on larvae of M. rufiventris developing inside the caterpillars. Our results confirm previous indications that naïve wasps may respond primarily to the green leaf volatile

Why rational argument fails the genetic modification (GM) debate

AbstractGenetic modification (GM) of crops provides a methodology for the agricultural improvements needed to deliver global food security. However, public opposition to GM-food is great. The debate has tended to risk communication, but here we show through study of a large nationally representative sample of British adults that public acceptance of GM-food has social, cultural and affective contexts. Regression models showed that metaphysical beliefs about the sanctity of food and an emotional dislike of GM-food were primary negative determinants, while belief in the value of science and favourable evaluation of the benefits-to-risks of GM-food were secondary positive determinants. Although institutional trust, general knowledge of the GM-food debate and belief in the eco-friendliness of GM-food were all associated with acceptance, their influence was minor. While a belief in the sanctity of food had a direct inverse effect on GM acceptance, belief in the value of science was largely mediated through favourable perception of benefits-to-risks. Furthermore, segmentation analysis demonstrated that anxiety about GM-food had social and cultural antecedents, with white men being least anxious and older vegetarian women being most anxious. Rational argument alone about the risks and benefits of GM-food is unlikely to change public perceptions of GM-technology

Interplay between JA, SA and ABA isgnalling during basal and induced resistance against pseudomonas syringae and Alternaria brasicicola

We have examined the role of the callose synthase PMR4 in basal resistance and β‐aminobutyric acid‐induced resistance (BABA‐IR) of Arabidopsis thaliana against the hemi‐biotrophic pathogen Pseudomonas syringae and the necrotrophic pathogen Alternaria brassicicola. Compared to wild‐type plants, the pmr4‐1 mutant displayed enhanced basal resistance against P. syringae, which correlated with constitutive expression of the PR‐1 gene. Treating the pmr4‐1 mutant with BABA boosted the already elevated levels of PR‐1 gene expression, and further increased the level of resistance. Hence, BABA‐IR against P. syringae does not require PMR4‐derived callose. Conversely, pmr4‐1 plants showed enhanced susceptibility to A. brassicicola, and failed to show BABA‐IR. Wild‐type plants showing BABA‐IR against A. brassicicola produced increased levels of JA. The pmr4‐1 mutant produced less JA upon A. brassicicola infection than the wild‐type. Blocking SA accumulation in pmr4‐1 restored basal resistance, but not BABA‐IR against A. brassicicola. This suggests that the mutant’s enhanced susceptibility to A. brassicicola is caused by SA‐mediated suppression of JA, whereas the lack of BABA‐IR is caused by its inability to produce callose. A. brassicicola infection suppressed ABA accumulation. Pre‐treatment with BABA antagonized this ABA accumulation, and concurrently potentiated expression of the ABA‐responsive ABI1 gene. Hence, BABA prevents pathogen‐induced suppression of ABA accumulation, and sensitizes the tissue to ABA, causing augmented deposition of PMR4‐derived callose

Impacts of atmospheric CO2 and soil nutritional value on plant responses to rhizosphere colonization by soil bacteria

Concerns over rising atmospheric CO2 concentrations have led to growing interest in the effects of global change on plant-microbe interactions. As a primary substrate of plant metabolism, atmospheric CO2 influences below-ground carbon allocation and root exudation chemistry, potentially affecting rhizosphere interactions with beneficial soil microbes. In this study, we have examined the effects of different atmospheric CO2 concentrations on Arabidopsis rhizosphere colonization by the rhizobacterial strain Pseudomonas simiae WCS417 and the saprophytic strain Pseudomonas putida KT2440. Rhizosphere colonization by saprophytic KT2440 was not influenced by sub-ambient (200 ppm) and elevated (1,200 ppm) concentrations of CO2, irrespective of the carbon (C) and nitrogen (N) content of the soil. Conversely, rhizosphere colonization by WCS417 in soil with relatively low C and N content increased from sub-ambient to elevated CO2. Examination of plant responses to WCS417 revealed that plant growth and systemic resistance varied according to atmospheric CO2 concentration and soil-type, ranging from growth promotion with induced susceptibility at sub-ambient CO2, to growth repression with induced resistance at elevated CO2. Collectively, our results demonstrate that the interaction between atmospheric CO2 and soil nutritional status has a profound impact on plant responses to rhizobacteria. We conclude that predictions about plant performance under past and future climate scenarios depend on interactive plant responses to soil nutritional status and rhizobacteria

Phloem: the integrative avenue for resource distribution, signaling, and defense.

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The genetic and epigenetic landscape of the Arabidopsis centromeres.

Centromeres attach chromosomes to spindle microtubules during cell division and, despite this conserved role, show paradoxically rapid evolution and are typified by complex repeats. We used longread sequencing to generate the Col-CEN Arabidopsis thaliana genome assembly that resolves all five centromeres. The centromeres consist of megabase-scale tandemly repeated satellite arrays, which support CENH3 occupancy and are densely DNA methylated, with satellite variants private to each chromosome. CENH3 preferentially occupies satellites that show least divergence and occur in higherorder repeats. The centromeres are invaded by ATHILA retrotransposons, which disrupt genetic and epigenetic organization. Centromeric crossover recombination is suppressed, yet low levels of meiotic DSBs occur that are regulated by DNA methylation. We propose that Arabidopsis centromeres are evolving via cycles of satellite homogenization and retrotransposon-driven diversification.BBSRC grants BB/S006842/1, BB/S020012/1 and BB/V003984/1