Involvement of auxin pathways in modulating root architecture during beneficial plant–microorganism interactions

A wide variety of microorganisms known to produce auxin and auxin precursors form beneficial relationships with plants and alter host root development. Moreover, other signals produced by microorganisms affect auxin pathways in host plants. However, the precise role of auxin and auxin‐signalling pathways in modulating plant–microbe interactions is unknown. Dissecting out the auxin synthesis, transport and signalling pathways resulting in the characteristic molecular, physiological and developmental response in plants will further illuminate upon how these intriguing inter‐species interactions of environmental, ecological and economic significance occur. The present review seeks to survey and summarize the scattered evidence in support of known host root modifications brought about by beneficial microorganisms and implicate the role of auxin synthesis, transport and signal transduction in modulating beneficial effects in plants. Finally, through a synthesis of the current body of work, we present outstanding challenges and potential future research directions on studies related to auxin signalling in plant–microbe interactions.     

Evolution of the population structure of Venturia inaequalis,the apple scab fungus,associated with the domestication of its host

Evaluating the impact of plant domestication on the population structure of the associated pathogens provides an opportunity to increase our understanding of how and why diseases emerge. Here, we investigated the evolution of the population structure of the apple scab fungus Venturia inaequalis in response to the domestication of its host. Inferences were drawn from multilocus microsatellite data obtained from samples collected on (i) the Central Asian Malus sieversii, the main progenitor of apple, (ii) the European crabapple, Malus sylvestris, a secondary progenitor of apple, and (iii) the cultivated apple, Malus×domestica, in orchards from Europe and Central Asia. Using clustering methods, we identified three distinct populations: (i) a large European population on domesticated and wild apples, (ii) a large Central Asian population on domesticated and wild apples in urban and agricultural areas, and (iii) a more geographically restricted population in M. sieversii forests growing in the eastern mountains of Kazakhstan. Unique allele richness and divergence time estimates supported a host‐tracking co‐evolutionary scenario in which this latter population represents a relict of the ancestral populations from which current populations found in human‐managed habitats were derived. Our analyses indicated that the domestication of apple induced a significant change in the genetic differentiation of populations of V. inaequalis in its centre of origin, but had little impact on its population dynamics and mating system. We discuss how the structure of the apple‐based agrosystem may have restricted changes in the population structure of the fungus in response to the domestication of its host.     

Answer to “Reevaluation of the conclusion that IRES-activity reported within the 5′ leader of the TIF4631 gene is due to promoter activity”

The accuracy of the data we reported in an RNA Letter to the Editor earlier this year on the promoter activity within the 5′ leader of the TIF4631 gene is questioned by V.P. Mauro and others in this issue. We reply here that we see no inaccuracy in our data.     

Ommochrome Deficiency in an Albino Strain of a Terrestrial Isopod,Armadillidium vulgare

In order to clarify the cause of ommochrome deficiency in an albino strain of the terrestrial isopod, Armadillidium vulgare, levels of xanthom-matin, 3-hydroxykynurenine, 3-hydroxyanthranilic acid and tryptophan in whole body extracts of the albino and the wild type individuals were determined together with enzyme activities of kynurenine-3-hydroxylase, kynureninase and tryptophan-2,3-dioxygenase. Xanthommatin could not be detected in the albinos. The levels of 3-hydroxykynurenine and 3-hydroxyanthranilic acid were determined by high-performance liquid chro-matography (HPLC) with electrochemical detection and were markedly low in the albinos compared with the wild type individuals. In contrast to those, the tryptophan levels determined by HPLC with fluorescence detection did not differ significantly between the two phenotypes. In the albino A. vulgare, kynurenine-3-hydroxylase activity was lower and kynureninase activity was higher than in the wild type, although the differences were not statistically significant. Tryptophan-2,3-dioxygenase activity in the albinos was less than 10% that in the wild type. Thus, ommochrome deficiency in the albino A. vulgare is considered to be caused by the extremely low activity of tryptophan-2,3-dioxygenase.     

IL-1 MODIFIES SYSTEM A TRANSPORT ACTIVITY IN HUMAN RHEUMATOID SYNOVIAL CELLS

Given the importance of interleukin-1 in both rheumatic diseases and the modulation of cell metabolic activities, we studied the action of this cytokine on the neutral amino acid transport A system on rheumatoid synovial cells. In these cells IL-1 (1ng/ml) induced amino transport stimulation from 5min to 5h. This effect was obtained only after a starvation period. No concentration-related effect was found for IL-1-stimulated MeAIB uptake, and the IL-1-mediated MeAIB uptake stimulation is independent of protein synthesis. Neosynthesis or post-translational maturation of protein transport is a prerequisite for obtaining this effect. In conclusion, rheumatoid synovial cells exhibit a higher sensitivity for IL-1 than osteoarthritic ones, probably related to their intense metabolic activity.     

Carbon dynamics in topsoil and in subsoil may be controlled by different regulatory mechanisms

It is estimated that in excess of 50% of the soil carbon stock is found in the subsoil (below 20–30 cm). Despite this very few studies have paid attention to the subsoil. Although surface and subsurface horizons differ in pedological, environmental and physicochemical features, which are all likely to affect the mechanisms and biological actors involved, models of carbon dynamics tend to assume that the underlying processes are identical in all horizons, but with lower gross fluxes in the subsurface. The aim of this study was to test this assumption by analysing factors governing organic matter decomposition in topsoil (from depths of 5–10 cm) and subsoil (from depths of 80–100 cm). To this end, we established incubations that lasted 51 days, in which factors that were thought to control organic matter mineralization were altered: oxygen concentration, soil structure and the energetic and nutritional status. At the end of the incubation period, the microbial biomass was measured and the community level physiological profiles established. The mineralization per unit organic carbon proved to be as important in the subsoil as it was in surface samples, in spite of lower carbon contents and different catabolic profiles. Differences in the treatment effects indicated that the controls on C dynamics were different in topsoil and subsoil: disrupting the structure of the subsoil caused a 75% increase in mineralization while the surface samples remained unaffected. On the other hand, a significant priming affect was found in the topsoil but not in the subsoil samples. Spatial heterogeneity in carbon content, respiration and microbial communities was greater in subsoil than in topsoil at the field scale. These data suggest greater attention should be paid to the subsoil if global C dynamics is to be fully understood.     

Discongruence of Mhc and cytochrome b phylogeographical patterns in Myodes glareolus (Rodentia: Cricetidae)

In the present study, a phylogeographical approach was developed to analyse the influence of selection and history on a major histocompatibility complex (Mhc) class II gene polymorphism in European bank vole (Myodes glareolus) populations. We focused on exon 2 of the Dqa gene because it is highly variable in a large array of species and appears to evolve under pathogen‐mediated selection in several rodent species. Using single‐strand conformation polymorphism analysis and sequencing techniques, 17 Dqa‐exon2 alleles, belonging to at least two different copies of Dqa gene, were detected over the distribution range of M. glareolus. Evidence of selection was found using molecular and population analyses. At the molecular level, we detected 13 codons evolving under positive selection pressures, most of them corresponding to regions coding for putative antigen binding sites of the protein. At the European level, we compared patterns of population structure for the Dqa‐exon2 and cytochrome b (cyt b) gene. We did not detect any spatial genetic structure among M. glareolus populations for the Dqa‐exon2. These results strongly differed from those obtained using the cyt b gene, which indicated a recent phylogeographical history closely linked to the last glacial events. Seven mitochondrial lineages have yet been described, which correspond to major glacial refugia. Altogether, our results revealed clear evidence of balancing selection acting on Dqa‐exon2 and maintaining polymorphism over large geographical areas despite M. glareolus history. It is thus likely that Mhc phylogeographical variability could have been shaped by local adaptation to pathogens. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 881–899.     

A THEORETICAL NOTE ON DIFFERENCE TESTS: MODELS, PARADOXES AND COGNITIVE STRATEGIES

A simple nonmathematical introduction is given to Thurstonian modeling and its application to difference testing. The theoretical treatment explains differences in performance noted for various difference test protocols and the so-called paradox of discriminatory nondiscriminators, whereby a slight change in instructions to the judge can alter the proportion of tests performed correctly. From this, the assumptions in the use of binomial statistics for analyzing difference tests and their shortcomings, are discussed. New ideas on the generality of the paradox of discriminatory nondiscriminators are discussed, along with the effects of the cognitive strategy adopted by the judge during testing.