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Pathogen Invasion (pathogen + invasion)
Selected AbstractsPERSPECTIVE: Rethinking the value of high wood densityFUNCTIONAL ECOLOGY, Issue 4 2010Markku Larjavaara Summary 1.,Current thinking holds that wood density mediates a tradeoff between strength and economy of construction, with higher wood density providing higher strength but at higher cost. 2.,Yet the further away wood fibres are from the central axis of the trunk, the more they increase the strength of the trunk; thus, a fat trunk of low-density wood can achieve greater strength at lower construction cost than a thin trunk of high-density wood. 3.,What then are the countervailing advantages of high wood density? 4.,We hypothesize that high wood density is associated with lower maintenance costs due to lower trunk surface area, as surface area correlates with maintenance respiration. 5.,This advantage would be particularly important to long-lived trees and could in part explain why they tend to have high wood density. 6.,High wood density has also been associated with lower risk of trunk breakage, xylem implosion and pathogen invasion, but we argue that these relationships are not causal and instead reflect correlated selection on other traits of value to long-lived trees. 7.,This revaluation of the costs and benefits of high wood density has important implications for understanding tree life-history evolution, functional diversity, forest carbon stocks and the impacts of global change. [source] Two modes of ERK activation by TNF in keratinocytes: Different cellular outcomes and bi-directional modulation by vitamin D,JOURNAL OF CELLULAR BIOCHEMISTRY, Issue 2 2008Ester Ziv Abstract Inflammation, elicited in the skin following tissue damage or pathogen invasion, may become chronic with deleterious consequences. Tumor necrosis factor (TNF) is a key mediator of cutaneous inflammation and the keratinocyte an important protagonist of skin immunity. Calcitriol, the hormonally active vitamin D metabolite, and its analogs attenuate epidermal inflammation and inhibit the hyperproliferation of keratinocytes associated with the inflammatory disorder, psoriasis. Since activation of extracellular signal-regulated kinase (ERK) promotes keratinocyte proliferation and mediates epidermal inflammation, we studied the effect of calcitriol on ERK activation in HaCaT keratinocytes exposed to the ubiquitous inflammatory cytokine TNF. By using the EGF receptor (EGFR) tyrosine kinase inhibitor, AG1487 and the Src family inhibitor, PP-1, we established that TNF activated ERK in an EGFR and Src dependent and an EGFR and Src independent modes. EGFR dependent activation resulted in the upregulation of the transcription factor, c-Fos, while the EGFR independent activation mode was of a shorter duration, did not affect c-Fos expression but induced IL-8 mRNA expression. Pretreatment with calcitriol, enhanced TNF-induced EGFR-Src dependent ERK activation and tyrosine phosphorylation of the EGFR, but abolished the EGFR-Src independent ERK activation. These effects were mirrored by enhancement of c-Fos and inhibition of IL-8 induction by TNF. Treatment with calcitriol increased the rate of the de-phosphorylation of activated ERK, accounting for the inhibition of EGFR-Src independent ERK activation by TNF. It is possible that effects on the ERK cascade contribute to the effects of calcitriol and its synthetic analogs on cutaneous inflammation and keratinocyte proliferation. J. Cell. Biochem. 104: 606,619, 2008. © 2007 Wiley-Liss, Inc. [source] The expression, function and regulation of mitochondrial alternative oxidase under biotic stressesMOLECULAR PLANT PATHOLOGY, Issue 3 2010FENG HANQING SUMMARY To survive, plants possess elaborate defence mechanisms to protect themselves against virus or pathogen invasion. Recent studies have suggested that plant mitochondria may play an important role in host defence responses to biotic stresses. In contrast with animal mitochondria, plant mitochondria possess a unique respiratory pathway, the cyanide-insensitive alternative pathway, which is catalysed by the alternative oxidase (AOX). Much work has revealed that the genes encoding AOX, AOX protein and the alternative respiratory pathway are frequently induced during plant,pathogen (or virus) interaction. This raises the possibility that AOX is involved in host defence responses to biotic stresses. Thus, a key to the understanding of the role of mitochondrial respiration under biotic stresses is to learn the function and regulation of AOX. In this article, we focus on the theoretical and experimental progress made in the current understanding of the function and regulation of AOX under biotic stresses. We also address some speculative aspects to aid further research in this area. [source] A new catalytic activity from tobacco converting 2-coumaric acid to salicylic aldehydePHYSIOLOGIA PLANTARUM, Issue 3 2007Jacek Malinowski Salicylic acid (SA) mediates plant response to pathogen invasion, resulting in hypersensitive response and in the formation of systemic acquired resistance. It is well known that Nicotiana tabacum and other plants respond to Tobacco Mosaic Virus (TMV) infection by increasing the content of SA but the details of SA biosynthesis are still not fully understood. Generally, SA may originate directly from isochorismate (Arabidopsis thaliana), or its C6,C1 skeleton could be synthesized via the phenylpropanoid pathway by ,-oxidation of trans -cinnamic acid (N. tabacum), 2-coumaric acid (OCA) (Gaulteria procumbens, Lycopersicum esculentum) or by retro-aldol reaction of trans -cinnamoyl-CoA (Hypericum androsaemum). We report here a novel putative enzyme activity from tobacco, salicylic aldehyde synthase (SAS), catalysing non-oxidative formation of salicylic aldehyde (SALD) directly from OCA. This chain-shortening activity is similar to that of 4-hydroxybenzaldehyde synthase from Vanilla planifolia, Lithospermum erythrorhizon, Daucus carota, Solanum tuberosum and Polyporus hispidus but the enzyme differs in the kinetics of the reaction, substrate specificity and requirements for reducing cofactors. SAS activity is constitutively expressed in healthy tobacco leaves and doubles as a result of infection with TMV. Moreover, the product of SAS activity,SALD, applied exogenously on tobacco leaves, stimulates peroxidase activity and enhances resistance to consecutive infection with TMV. These observations could suggest a contribution of SAS and SALD to the response of tobacco to TMV infection. [source] REVIEW ARTICLE: Toll-Like Receptor Signaling and Pre-EclampsiaAMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY, Issue 1 2010Fang Xie Systemic inflammation and abnormal/poor placentation represent hallmarks of pre-eclampsia. Accumulating evidence suggests that infectious agents might increase the risk of pre-eclampsia; the innate immune defense mechanisms may interact with pro-inflammatory pathways, and contribute to the development of pre-eclampsia. The evidence for this has been supported by indirect epidemiologic and clinical studies, as well as by some direct support from experimental studies. Recent data directly implicate signaling by Toll-like receptors in the pathogenesis of pre-eclampsia, and establish a crucial link between pre-eclampsia and defense against both foreign pathogens and endogenously generated inflammatory ligands. Here, we review the rapid progress in this field, which has improved our understanding of the interplay between pathogen invasion, innate immune defense mechanisms, and pre-eclampsia. [source] | ||||||||||