The role of volatiles in plant communication

Volatiles mediate the interaction of plants with pollinators, herbivores and their natural enemies, other plants and micro‐organisms. With increasing knowledge about these interactions the underlying mechanisms turn out to be increasingly complex. The mechanisms of biosynthesis and perception of volatiles are slowly being uncovered. The increasing scientific knowledge can be used to design and apply volatile‐based agricultural strategies.     

The mitochondrial NAD+ transporter (NDT1) plays important roles in cellular NAD+ homeostasis in Arabidopsis thaliana

Nicotinamide adenine dinucleotide (NAD⁺) is an essential coenzyme required for all living organisms. In eukaryotic cells, the final step of NAD⁺ biosynthesis is exclusively cytosolic. Hence, NAD⁺ must be imported into organelles to support their metabolic functions. Three NAD⁺ transporters belonging to the mitochondrial carrier family (MCF) have been biochemically characterized in plants. AtNDT1 (At2g47490), focus of the current study, AtNDT2 (At1g25380), targeted to the inner mitochondrial membrane, and AtPXN (At2g39970), located in the peroxisomal membrane. Although AtNDT1 was presumed to reside in the chloroplast membrane, subcellular localization experiments with green fluorescent protein (GFP) fusions revealed that AtNDT1 locates exclusively in the mitochondrial membrane in stably transformed Arabidopsis plants. To understand the biological function of AtNDT1 in Arabidopsis, three transgenic lines containing an antisense construct of AtNDT1 under the control of the 35S promoter alongside a T‐DNA insertional line were evaluated. Plants with reduced AtNDT1 expression displayed lower pollen viability, silique length, and higher rate of seed abortion. Furthermore, these plants also exhibited an increased leaf number and leaf area concomitant with higher photosynthetic rates and higher levels of sucrose and starch. Therefore, lower expression of AtNDT1 was associated with enhanced vegetative growth but severe impairment of the reproductive stage. These results are discussed in the context of the mitochondrial localization of AtNDT1 and its important role in the cellular NAD⁺ homeostasis for both metabolic and developmental processes in plants.     

Orexin in the Posterior Paraventricular Thalamus Mediates Hunger-Related Signals in the Nucleus Accumbens Core

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Neutral loss-based phosphopeptide recognition: a collection of caveats

The standard strategy for analysis by tandem mass spectrometry of protein phosphorylation at serine or threonine utilizes the neutral loss of H3PO4 (= 97.977/z) from proteolytic peptide molecular ions as marker fragmentation. Manual control of automatically performed neutral loss-based phosphopeptide identifications is strongly recommended, since these data may contain false-positive results. These are connected to the experimental neutral loss m/z error, to competing peptide fragmentation pathways, to limitations in data interpretation software, and to the general growth of protein sequence databases. The fragmentation-related limitations of the neutral loss approach cover (i) the occurrence of abundant 'close-to-98/z' neutral loss fragmentations, (ii) the erroneous assignment of a neutral loss other than loss of H3PO4 due to charge state mix-up, and (iii) the accidental occurrence of any fragment ion in the m/z windows of interest in combination with a charge-state mix-up. The 'close-to-98/z' losses comprise loss of proline (97.053/z), valine (99.068/z), threonine (101.048/z), or cysteine (103.009/z) preferably from peptides with N-terminal sequences PP, VP, TP, or CP, and loss of 105.025/z from alkylated methionine. Confusion with other neutral losses may occur, when their m/z window coincides with a 98/z window as result of a charge state mix-up. Neutral loss of sulfenic acid from oxidized methionine originating from a doubly charged precursor (63.998/2 = 31.999) may thus mimic the loss of phosphoric acid from a triply charged phosphopeptide (97.977/3 = 32.659). As a consequence of the large complexity of proteomes, peptide sequence ions may occur in one of the mass windows of H3PO4 loss around 97.977/z. Practical examples for false-positive annotations of phosphopeptides are given for the first two groups of error. The majority of these can be readily recognized using the guidelines presented in this study.     

Experimental design for efficient identification of gene regulatory networks using sparse Bayesian models

Background  

Identifying large gene regulatory networks is an important task, while the acquisition of data through perturbation experiments (e.g., gene switches, RNAi, heterozygotes) is expensive. It is thus desirable to use an identification method that effectively incorporates available prior knowledge – such as sparse connectivity – and that allows to design experiments such that maximal information is gained from each one.     

Endogenous pararetroviral sequences in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis>) and related species

Background  

Endogenous pararetroviral sequences (EPRVs) are a recently discovered class of repetitive sequences that is broadly distributed in the plant kingdom. The potential contribution of EPRVs to plant pathogenicity or, conversely, to virus resistance is just beginning to be explored. Some members of the family Solanaceae are particularly rich in EPRVs. In previous work, EPRVs have been characterized molecularly in various species of Nicotiana including N.tabacum (tobacco) and Solanum tuberosum (potato). Here we describe a family of EPRVs in cultivated tomato (Solanum lycopersicum L.) and a wild relative (S.habrochaites).     

Intracellular trafficking of Potato leafroll virus movement protein in transgenic Arabidopsis

Intracellular trafficking of viral movement proteins (MPs) in plants has mainly been studied using Tobacco mosaic virus MP30 (TMV MP30) as a model system. Because of the limitations of TMV MP30 expression in Arabidopsis thaliana, these studies have mostly been restricted to tobacco plants. Here we present data on the analysis of transgenic Arabidopsis plants expressing Potato leafroll virus 17-kDa movement protein (MP17) fused to green fluorescent protein. MP17 localizes to secondary branched plasmodesmata (PD) in source but not to simple PD in sink tissues, where MP17 is believed to be degraded by proteolysis. To unravel the intracellular transport path of MP17, we analyzed the relevance of the cytoskeleton and of the secretory pathway on MP17 targeting. To this end, a new incubation system for in vivo analysis of immediate and long-term responses of whole Arabidopsis plants to inhibitor treatments was established. Microscopic and histochemical analysis showed that MP17 is targeted to PD in an actin- and endoplasmic reticulum-Golgi-dependent manner. In contrast, degradation of MP17 in sink tissues required intact microtubules and occurred at 26S proteasomes. Interestingly, inhibition of the 26S proteasome led to aggregation of MP17 in aggresome-like structures. Formation of these structures could be inhibited by colchicine, as was shown for aggresomes in mammalian cells.     

Antigen-Specific Th17 Cells Are Primed by Distinct and Complementary Dendritic Cell Subsets in Oropharyngeal Candidiasis

Candida spp. can cause severe and chronic mucocutaneous and systemic infections in immunocompromised individuals. Protection from mucocutaneous candidiasis depends on T helper cells, in particular those secreting IL-17. The events regulating T cell activation and differentiation toward effector fates in response to fungal invasion in different tissues are poorly understood. Here we generated a Candida-specific TCR transgenic mouse reactive to a novel endogenous antigen that is conserved in multiple distant species of Candida, including the clinically highly relevant C. albicans and C. glabrata. Using TCR transgenic T cells in combination with an experimental model of oropharyngeal candidiasis (OPC) we investigated antigen presentation and Th17 priming by different subsets of dendritic cells (DCs) present in the infected oral mucosa. Candida-derived endogenous antigen accesses the draining lymph nodes and is directly presented by migratory DCs. Tissue-resident Flt3L-dependent DCs and CCR2-dependent monocyte-derived DCs collaborate in antigen presentation and T cell priming during OPC. In contrast, Langerhans cells, which are also present in the oral mucosa and have been shown to prime Th17 cells in the skin, are not required for induction of the Candida-specific T cell response upon oral challenge. This highlights the functional compartmentalization of specific DC subsets in different tissues. These data provide important new insights to our understanding of tissue-specific antifungal immunity.     

Association of vectors and environmental conditions during the emergence of Peruvian horse sickness orbivirus and Yunnan orbivirus in northern Peru

Since 1983, cases of diseased donkeys and horses with symptoms similar to those produced by alphaviruses were identified in two departments in northern Peru; however serological testing ruled out the presence of those viruses and attempts to isolate an agent were also unproductive. In 1997, also in northern Peru, two new orbiviruses were discovered, each recognized as a causative agent of neurological diseases in livestock and domestic animals and, at the same time, mosquitoes were found to be infected with these viruses. Peruvian horse sickness virus (PHSV) was isolated from pools of culicid mosquitoes, Aedes serratus and Psorophora ferox, and Yunnan virus (YUOV) was isolated from Aedes scapularis in the subtropical jungle (upper jungle) located on the slope between the east side of the Andes and the Amazonian basin in the Department of San Martín. Both viruses later were recovered from mosquitoes collected above the slope between the west side of the Andes and the coast (Department of Piura) in humid subtropical areas associated with the Piura River basin. In this region, PHSV was isolated from Anopheles albimanus and YUOV was isolated from Ae. scapularis. We discuss the ecology of vector mosquitoes during the outbreaks in the areas where these mosquitoes were found.