Resistance to rust fungi in Lolium perenne depends on within-species variation and performance of the host species in grasslands of different plant diversity

The hypothesis that plant species diversity and genetic variation of the host species decrease the severity of plant diseases is supported by studies of agricultural systems, but experimental evidence from more complex systems is scarce. In an experiment with grassland communities of varying species richness (1, 2, 4, 8, 16, and 60 species) and functional group richness (1, 2, 3, and 4 functional groups), we used different cultivars of Lolium perenne (perennial ryegrass) to study effects of biodiversity and cultivar identity on the occurrence and severity of foliar fungal diseases caused by Puccinia coronata (crown rust) and P. graminis (stem rust). Cultivar monocultures of perennial ryegrass revealed strong differences in pathogen susceptibility among these cultivars. Disease intensity caused by both rust fungi decreased significantly with growing species richness of species mixtures. The response to the diversity gradient was related to the decreased density and size of the host individuals with increasing species richness. The occurrence of other grass species known to be possible hosts of the pathogens in the experimental mixtures did not promote disease intensity in L. perenne, indicating that there was a high host specificity of pathogen strains. Differences in pathogen susceptibility among perennial ryegrass cultivars persisted independent of diversity treatment, host density and host individual size, but resulted in a cultivar-specific pattern of changes in pathogen infestation across the species-richness gradient. Our study provided evidence that within-species variation in pathogen susceptibility and competitive interactions of the host species with the environment, as caused by species diversity treatments, are key determinants of the occurrence and severity of fungal diseases. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Developmental genes have pleiotropic effects on plant morphology and source capacity, eventually impacting on seed protein content and productivity in pea

Increasing pea (Pisum sativum) seed nutritional value and particularly seed protein content, while maintaining yield, is an important challenge for further development of this crop. Seed protein content and yield are complex and unstable traits, integrating all the processes occurring during the plant life cycle. During filling, seeds are the main sink to which assimilates are preferentially allocated at the expense of vegetative organs. Nitrogen seed demand is satisfied partly by nitrogen acquired by the roots, but also by nitrogen remobilized from vegetative organs. In this study, we evaluated the respective roles of nitrogen source capacity and sink strength in the genetic variability of seed protein content and yield. We showed in eight genotypes of diverse origins that both the maximal rate of nitrogen accumulation in the seeds and nitrogen source capacity varied among genotypes. Then, to identify the genetic factors responsible for seed protein content and yield variation, we searched for quantitative trait loci (QTL) for seed traits and for indicators of sink strength and source nitrogen capacity. We detected 261 QTL across five environments for all traits measured. Most QTL for seed and plant traits mapped in clusters, raising the possibility of common underlying processes and candidate genes. In most environments, the genes Le and Afila, which control internode length and the switch between leaflets and tendrils, respectively, determined plant nitrogen status. Depending on the environment, these genes were linked to QTL of seed protein content and yield, suggesting that source-sink adjustments depend on growing conditions.     

Production of the endocannabinoids anandamide and 2-arachidonoylglycerol by endothelial progenitor cells

Recent studies have highlighted the importance of paracrine growth factors as mediators of pro-angiogenic effects by endothelial progenitor cells (EPCs), but little is known about the release of lipid-based factors like endocannabinoids by EPCs. In the current study, the release of the endocannabinoids anandamide and 2-arachidonoylglycerol by distinct human EPC sub-types was measured using HPLC/tandem mass-spectrometry. Anandamide release was highest by adult blood colony-forming EPCs at baseline and they also demonstrated increased 2-arachidonoylglycerol release with TNF-alpha stimulation. Treatment of mature endothelial cells with endocannabinoids significantly reduced the induction of the pro-inflammatory adhesion molecule CD106 (VCAM-1) by TNF-alpha.     

Unraveling tissue regeneration pathways using chemical genetics

Identifying the molecular pathways that are required for regeneration remains one of the great challenges of regenerative medicine. Although genetic mutations have been useful for identifying some molecular pathways, small molecule probes of regenerative pathways might offer some advantages, including the ability to disrupt pathway function with precise temporal control. However, a vertebrate regeneration model amenable to rapid throughput small molecule screening is not currently available. We report here the development of a zebrafish early life stage fin regeneration model and its use in screening for small molecules that modulate tissue regeneration. By screening 2000 biologically active small molecules, we identified 17 that specifically inhibited regeneration. These compounds include a cluster of glucocorticoids, and we demonstrate that transient activation of the glucocorticoid receptor is sufficient to block regeneration, but only if activation occurs during wound healing/blastema formation. In addition, knockdown of the glucocorticoid receptor restores regenerative capability to nonregenerative, glucocorticoid-exposed zebrafish. To test whether the classical anti-inflammatory action of glucocorticoids is responsible for blocking regeneration, we prevented acute inflammation following amputation by antisense repression of the Pu.1 gene. Although loss of Pu.1 prevents the inflammatory response, regeneration is not affected. Collectively, these results indicate that signaling from exogenous glucocorticoids impairs blastema formation and limits regenerative capacity through an acute inflammation-independent mechanism. These studies also demonstrate the feasibility of exploiting chemical genetics to define the pathways that govern vertebrate regeneration.     

Toc159- and Toc75-independent import of a transit sequence-less precursor into the inner envelope of chloroplasts

Chloroplast envelope quinone oxidoreductase (ceQORH) is an inner plastid envelope protein that is synthesized without cleavable chloroplast transit sequence for import. In the present work, we studied the in vitro-import characteristics of Arabidopsis ceQORH. We demonstrate that ceQORH import requires ATP and is dependent on proteinaceous receptor components exposed at the outer plastid surface. Competition experiments using small subunit precursor of ribulose-bisphosphate carboxylase/oxygenase and precursor of ferredoxin, as well as antibody blocking experiments, revealed that ceQORH import does not involve the main receptor and translocation channel proteins Toc159 and Toc75, respectively, which operate in import of proteins into the chloroplast. Molecular dissection of the ceQORH amino acid sequence by site-directed mutagenesis and subsequent import experiments in planta and in vitro highlighted that ceQORH consists of different domains that act concertedly in regulating import. Collectively, our results provide unprecedented evidence for the existence of a specific import pathway for transit sequence-less inner plastid envelope membrane proteins into chloroplasts.     

Hairy attachment structures in Reduviidae (Cimicomorpha, Heteroptera), with observations on the fossula spongiosa in some other Cimicomorpha

Reduviidae and some other groups of cimicomorphan Heteroptera possess a hairy attachment structure on the apex of the tibia called “fossula spongiosa”. The fossula spongiosa was never studied comparatively across Reduviidae, its fine structure and mode of function is not well documented, and attachment structures in immature stages are virtually unknown. Here, a sample of 171 species of Reduviidae representing 22 subfamilies is examined for presence-absence of the fossula spongiosa on the three pairs of legs. Representatives of 11 of the 22 subfamilies are shown to possess a fossula spongiosa. The fine structure of the fossula spongiosa is examined for a more limited sample of Reduviidae and several Pachynomidae and Nabidae. In addition, scanning micrographs for the fossula spongiosa in other Cimicomorpha are given, among them Anthocoridae, Cimicidae, Microphysidae (first record of a fossula spongiosa), and Thaumastocoridae. The fossula spongiosa in Reduviidae consists of tenent hairs (acanthae) with spatulate or tapering apices interspersed with sensory setae, both of which are embedded in a thick and flexible cuticle, underlain by a hemolymph cavity separated almost entirely from the interior of the remaining tibia by a cuticular invagination. Judging from comparison with non-reduviid Cimicomorpha, this separation of the fossula spongiosa cavity from the tibial interior may be unique to Reduviidae. A simple experiment using live specimens of Platymeris biguttata (Reduviinae) revealed a liquid on the tip of the tenent hairs that might be involved in the attachment of the fossula spongiosa by adhesion mechanisms. The nymphs of Reduviidae whose adults have a fossula spongiosa are here documented for the first time to possess pads of ventrally barbed setae instead of tenent hairs and their tibia lacks the internal cuticular invagination. The nymphal attachment structures seem to rely on increase of friction rather than the adhesion mechanism proposed to be present in the adult. Combined with the tenent setae on the third tarsomere known in some Emesinae and here documented for Saicinae, three types of hairy attachment structures occur on the legs of Reduviidae: tenent hairs (acanthae), which form the fossula spongiosa in many Reduviidae, barbed setae that substitute the fossula in the immatures, and tenent setae on the tarsus which are restricted to only a few taxa.     

The PsbP-like protein (sll1418) of Synechocystis sp. PCC 6803 stabilises the donor side of Photosystem II

The PsbP-like protein of the cyanobacterium Synechocystis sp. PCC 6803 is a peripheral component of Photosystem II, located at the lumenal side of the thylakoid membrane. Removal of this protein leads to decreased competitive potential of a PsbP-like deletion mutant when grown in a mixture with wild-type cells. Flash-induced oxygen evolution traces of the mutant show a higher probability of misses, correlated with increased amplitudes of the S-states decay in the dark. Thermoluminescence emission traces demonstrate a changed charge recombination pattern in the mutant, the S(3)Q(B)(-) couple becoming the major species instead of the S(2)Q(B)(-). Our data suggest a possible role of the PsbP-like protein in stabilisation of the charge separation in Photosystem II of cyanobacteria through interaction with the Mn cluster.