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No abstract

Herbivore feeding elicits defense responses in infested plants, including the emission of volatile organic compounds that can serve as indirect defense signals. Until now, the contribution of plant tissue wounding during the feeding process in the elicitation of defense responses has not been clear. For example, in lima bean (Phaseolus lunatus), the composition of the volatiles induced by both the insect caterpillar Spodoptera littoralis and the snail Cepaea hortensis is very similar. Thus, a mechanical caterpillar, MecWorm, has been designed and used in this study, which very closely resembles the herbivore-caused tissue damage in terms of similar physical appearance and long-lasting wounding period on defined leaf areas. This mode of treatment was sufficient to induce the emission of a volatile organic compound blend qualitatively similar to that as known from real herbivore feeding, although there were significant quantitative differences for a number of compounds. Moreover, both the duration and the area that has been mechanically damaged contribute to the induction of the whole volatile response. Based on those two parameters, time and area, which can replace each other to some extent, a damage level can be defined. That damage level exhibits a close linear relationship with the accumulation of fatty acid-derived volatiles and monoterpenes, while other terpenoid volatiles and methyl salicylate respond in a nonlinear manner. The results strongly suggest that the impact of mechanical wounding on the induction of defense responses during herbivore feeding was until now underestimated. Controlled and reproducible mechanical damage that strongly resembles the insect's feeding process represents a valuable tool for analyzing the role of the various signals involved in the induction of plant defense reactions against herbivory.

Chloroplasts of land plants characteristically contain grana, cylindrical stacks of thylakoid membranes. A granum consists of a core of appressed membranes, two stroma-exposed end membranes, and margins, which connect pairs of grana membranes at their lumenal sides. Multiple forces contribute to grana stacking, but it is not known how the extreme curvature at margins is generated and maintained. We report the identification of the CURVATURE THYLAKOID1 (CURT1) protein family, conserved in plants and cyanobacteria. The four Arabidopsis thaliana CURT1 proteins (CURT1A, B, C, and D) oligomerize and are highly enriched at grana margins. Grana architecture is correlated with the CURT1 protein level, ranging from flat lobe-like thylakoids with considerably fewer grana margins in plants without CURT1 proteins to an increased number of membrane layers (and margins) in grana at the expense of grana diameter in overexpressors of CURT1A. The endogenous CURT1 protein in the cyanobacterium Synechocystis sp PCC6803 can be partially replaced by its Arabidopsis counterpart, indicating that the function of CURT1 proteins is evolutionary conserved. In vitro, Arabidopsis CURT1A proteins oligomerize and induce tubulation of liposomes, implying that CURT1 proteins suffice to induce membrane curvature. We therefore propose that CURT1 proteins modify thylakoid architecture by inducing membrane curvature at grana margins.

Aspergillus fumigatus is an important pathogen of the immunocompromised host causing pneumonia and invasive disseminated disease with high mortality. Previously, we identified a mutant strain (white, W) lacking conidial pigmentation and, in addition, the conidia showed a smooth surface morphology, whereas wild-type (WT) conidia are grey-green and have a typical ornamentation. W conidia appeared to be less protected against killing by the host defence, e.g., were more susceptible to oxidants in vitro and more efficiently damaged by human monocytes in vitro than WT conidia. When compared to the WT, the W mutant strain showed reduced virulence in a murine animal model. Genetic analysis suggested that the W mutant carried a single mutation which caused all of the observed phenotypes. Here. we report the construction of a genomic cosmid library of A. fumigatus and its use for complementation of the W mutant. Transformation of the W mutant was facilitated by co-transformation with plasmid pHELP1 carrying the autonomously replicating ama1 sequence of A. nidulans which also increased the transformation efficiency of A. fumigatus by a factor of 10. Using this cosmid library a putative polyketide synthase gene, designated pksP (polyketide synthase involved in pigment biosynthesis) was isolated. The pksP gene has a size of 6660 bp. pksP consists of five exons separated by short (47-73 bp) introns. Its deduced open reading frame is composed of 2146 amino acids. The pksP gene complemented both the white phenotype and the surface morphology of the W mutant conidia to wild type. Whereas W mutant conidia caused a strong reactive oxygen species (ROS) release by polymorphonuclear leukocytes, the ability of pksP-complemented W mutant conidia to stimulate ROS release was significantly reduced and comparable to that of WT conidia. In addition, the complemented strains showed restored virulence in a mouse model.

In chloroplasts, the transition metals iron and copper play an essential role in photosynthetic electron transport and act as cofactors for superoxide dismutases. Iron is essential for chlorophyll biosynthesis, and ferritin clusters in plastids store iron during germination, development, and iron stress. Thus, plastidic homeostasis of transition metals, in particular of iron, is crucial for chloroplast as well as plant development. However, very little is known about iron uptake by chloroplasts. Arabidopsis thaliana PERMEASE IN CHLOROPLASTS1 (PIC1), identified in a screen for metal transporters in plastids, contains four predicted a-helices, is targeted to the inner envelope, and displays homology with cyanobacterial permease-like proteins. Knockout mutants of PIC1 grew only heterotrophically and were characterized by a chlorotic and dwarfish phenotype reminiscent of iron-deficient plants. Ultrastructural analysis of plastids revealed severely impaired chloroplast development and a striking increase in ferritin clusters. Besides upregulation of ferritin, pic1 mutants showed differential regulation of genes and proteins related to iron stress or transport, photosynthesis, and Fe-S cluster biogenesis. Furthermore, PIC1 and its cyanobacterial homolog mediated iron accumulation in an iron uptake-defective yeast mutant. These observations suggest that PIC1 functions in iron transport across the inner envelope of chloroplasts and hence in cellular metal homeostasis.

The subject of geometric numerical integration deals with numerical integrators that preserve geometric properties of the flow of a differential equation, and it explains how structure preservation leads to improved long-time behaviour. This article illustrates concepts and results of geometric numerical integration on the important example of the Störmer-Verlet method. It thus presents a cross-section of the recent monograph by the authors, enriched by some additional material.After an introduction to the Newton-Störmer-Verlet-leapfrog method and its various interpretations, there follows a discussion of geometric properties: reversibility, symplecticity, volume preservation, and conservation of first integrals. The extension to Hamiltonian systems on manifolds is also described. The theoretical foundation relies on a backward error analysis, which translates the geometric properties of the method into the structure of a modified differential equation, whose flow is nearly identical to the numerical method. Combined with results from perturbation theory, this explains the excellent long-time behaviour of the method: long-time energy conservation, linear error growth and preservation of invariant tori in near-integrable systems, a discrete virial theorem, and preservation of adiabatic invariants. 400 E. Hairer, Ch. Lubich and G. Wanner CONTENTS