Does flooding favour galling insects?

New Perspectives is intended to allow the communication of comments, viewpoints, and speculative interpretation of issues in ecology pertinent to entomology. Comments, viewpoints, or suggestions arising from published papers intended to fuel discussion and debate are also welcome. Contributions should be as concise as possible, normally not exceeding two thousand words. Formal research reports will not be acceptable, but summarized novel data, suitably supported by statistics, may be allowed. The use of the active voice will be permitted.     

Fungal incompatibility: Evolutionary origin in pathogen defense?

In fungi, cell fusion between genetically unlike individuals triggers a cell death reaction known as the incompatibility reaction. In Podospora anserina, the genes controlling this process belong to a gene family encoding STAND proteins with an N‐terminal cell death effector domain, a central NACHT domain and a C‐terminal WD‐repeat domain. These incompatibility genes are extremely polymorphic, subject to positive Darwinian selection and display a remarkable genetic plasticity allowing for constant diversification of the WD‐repeat domain responsible for recognition of non‐self. Remarkably, the architecture of these proteins is related to pathogen‐recognition receptors ensuring innate immunity in plants and animals. Here, we hypothesize that these P. anserina incompatibility genes could be components of a yet‐unidentified innate immune system of fungi. As already proposed in the case of plant hybrid necrosis or graft rejection in mammals, incompatibility could be a by‐product of pathogen‐driven divergence in host defense genes.     

Response and adaptation by plants to flooding stress

Stress on plants imposed by flooding of the soil and deeper submergence constitutes one of the major abiotic constraints on growth, species' distribution and agricultural productivity. Flooding stress is also a strong driver of adaptive evolution. This has resulted in a wide range of biochemical, molecular and morphological adaptations that sanction growth and reproductive success under episodic or permanently flooded conditions that are highly damaging to the majority of plant species. However, even seemingly poorly adapted species possess some short-term resilience that is important for overall success of these plants in various habitats. The papers contained in this Special Issue address these topics and emphasize molecular, biochemical and developmental processes that impact on flooding tolerance. Most of the articles are based on lectures given to the 8th Conference of the International Society for Plant Anaerobiosis (ISPA), held at the University of Western Australia, Perth, 20-24 September, 2004. Reviews and research papers are presented from the leading laboratories currently working on plant responses to flooding stress.     

New insights into reactive oxygen species and nitric oxide signalling under low oxygen in plants

Plants produce reactive oxygen species (ROS) when exposed to low oxygen (O₂). Much experimental evidence has demonstrated the existence of an oxidative burst when there is an O₂ shortage. This originates at various subcellular sites. The activation of NADPH oxidase(s), in complex with other proteins, is responsible for ROS production at the plasma membrane. Another source of low O₂‐dependent ROS is the mitochondrial electron transport chain, which misfunctions when low O₂ limits its activity. Arabidopsis mutants impaired in proteins playing a role in ROS production display an intolerant phenotype to anoxia and submergence, suggesting a role in acclimation to stress. In rice, the presence of the submergence 1A (SUB1A) gene for submergence tolerance is associated with a higher capacity to scavenge ROS. Additionally, the destabilization of group VII ethylene responsive factors, which are involved in the direct O₂ sensing mechanism, requires nitric oxide (NO). All this evidence suggests the existence of a ROS and NO – low O₂ mechanism interplay which likely includes sensing, anaerobic metabolism and acclimation to stress. In this review, we summarize the most recent findings on this topic, formulating hypotheses on the basis of the latest advances.     

肺表面活性物质相关蛋白A与肺部免疫防御研究进展

肺表面活性物质相关蛋白A（SP—A）是一种高度保守的亲水性糖蛋白,属于C-型凝素家族成员,相对分子质量为29～36kDa。SP—A是肺部重要的天然免疫防御分子,在肺的局部防御和天然免疫反应中起着十分重要的作用。它不仅可调节局部免疫和炎症反应、调理吞噬作用,还可凝集病原微生物、影响趋化作用及促进杀菌作用等。     

Submergence-induced leaf acclimation in terrestrial species varying in flooding tolerance

Earlier work on the submergence-tolerant species Rumex palustris revealed that leaf anatomical and morphological changes induced by submergence enhance underwater gas exchange considerably. Here, the hypothesis is tested that these plastic responses are typical properties of submergence-tolerant species. Submergence-induced plasticity in leaf mass area (LMA) and leaf, cell wall and cuticle thickness was investigated in nine plant species differing considerably in tolerance to complete submergence. The functionality of the responses for underwater gas exchange was evaluated by recording oxygen partial pressures inside the petioles when plants were submerged. Acclimation to submergence resulted in a decrease in all leaf parameters, including cuticle thickness, in all species irrespective of flooding tolerance. Consequently, internal oxygen partial pressures (pO(2)) increased significantly in all species until values were close to air saturation. Only in nonacclimated leaves in darkness did intolerant species have a significantly lower pO(2) than tolerant species. These results suggest that submergence-induced leaf plasticity, albeit a prerequisite for underwater survival, does not discriminate tolerant from intolerant species. It is hypothesized that these plastic leaf responses may be induced in all species by several signals present during submergence; for example, low LMA may be a response to low photosynthate concentrations and a thin cuticle may be a response to high relative humidity.     

抗病毒免疫中干扰素与炎症信号通路的交互调控：防御反应与维持稳态

天然免疫是机体通过识别自身或外部危险信号后,为维持体内稳态而逐步建立起来的一系列防御反应,当宿主细胞内的模式识别受体识别胞内病原相关分子模式后激活干扰素(interferon, IFN)、核因子-kappa B (nuclear factor-kappa B, NF-κB)和炎性小体等信号通路。IFNs在天然免疫应答中发挥重要作用,它诱导的抗病毒基因能够通过多种方式抵御病毒的感染,炎症反应则是机体自动的防御反应,能够在病毒感染机体时释放促炎性细胞因子以调控机体的免疫反应,进而发挥抗病毒作用。在病毒感染过程中,IFN信号通路与炎症反应调控网络中的关键分子如NF-κB/RelA、PKR等存在一定的交互作用,此外,IFN信号通路及其产生的细胞因子又影响其他信号通路的活化,进而调控机体的免疫应答以维持自身稳态,它们之间的交互调控失衡将会引起过度炎症反应,导致组织器官的免疫病理损伤,例如SARS-CoV-2感染机体时产生的过度炎症反应。本文综述了机体抗病毒免疫过程中干扰素信号通路与炎症反应之间的交互调控,为研发抗病毒策略提供新思路。     

The ubiquitin ligation machinery in the defense against bacterial pathogens

The ubiquitin system is an important part of the host cellular defense program during bacterial infection. This is in particular evident for a number of bacteria including Salmonella Typhimurium and Mycobacterium tuberculosis which—inventively as part of their invasion strategy or accidentally upon rupture of seized host endomembranes—become exposed to the host cytosol. Ubiquitylation is involved in the detection and clearance of these bacteria as well as in the activation of innate immune and inflammatory signaling. Remarkably, all these defense responses seem to emanate from a dense layer of ubiquitin which coats the invading pathogens. In this review, we focus on the diverse group of host cell E3 ubiquitin ligases that help to tailor this ubiquitin coat. In particular, we address how the divergent ubiquitin conjugation mechanisms of these ligases contribute to the complexity of the anti‐bacterial coating and the recruitment of different ubiquitin‐binding effectors. We also discuss the activation and coordination of the different E3 ligases and which strategies bacteria evolved to evade the activities of the host ubiquitin system.     

Cell type-dependent requirement of autophagy in HSV-1 antiviral defense

Type I interferons (IFNs) are induced during most viral infections and are considered to be the primary and universal means of innate viral control. However, several other innate mechanisms, including autophagy, have recently been shown to play an important role in antiviral defense. In our recent study, we utilized a herpes simplex virus 1 (HSV-1) infection model to investigate the relationship between cell type and innate antiviral immune mechanisms. Our study demonstrates that dorsal root ganglion (DRG) neurons undergo an innate antiviral response to HSV-1 that differs from the antiviral program induced in mitotic cells in three distinct ways. First, DRG neurons produce less type I IFN and undergo a less effective IFN antiviral program vs. mitotic cells in response to HSV-1 infection. Second, the type I IFN program initiated in DRG neurons induces less cell death than in mitotic cells. Third, in the absence of a robust type I IFN response, DRG neurons, but not mitotic cells, repy on autophagy in HSV-1 defense. Our findings reveal a cell type-specific requirement for autophagy in defense against HSV-1, and offer insight into the cell-appropriate antiviral defense mechanism employed by neurons.     

Molecular and Physiological Mechanisms of Flooding Avoidance and Tolerance in Rice

Submergence is one of the major constraints in rice production. The main factor limiting rice survival during submergence is oxygen deprivation. To cope with flooding conditions, rice has developed two survival strategies: either rapid elongation of the submerged tissues to keep up with the rising water level or no elongation to save carbohydrate resources for maintenance of energy production under submerged and concomitant hypoxic conditions. The survival strategies used by rice have been studied quite extensively and the role of several phytohormones in the elongation response has been established. The mechanisms of submergence tolerance include metabolic changes, for instance, the shift to an ethanolic fermentation pathway, reduced elongation growth to save carbohydrates and energy for maintenance processes, and protective antioxidant systems. Current molecular technology can provide tools for the understanding of mechanisms developed by rice to survive submergence. In addition, cloning of genes related to submergence tolerance might open new ways to genetic improvement of this crop.     

The Receptor-like Cytoplasmic Kinase BIK1 Localizes to the Nucleus and Regulates Defense Hormone Expression during Plant Innate Immunity

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Antisense suppression of cucumber (Cucumis sativus L.) sucrose synthase 3 (CsSUS3) reduces hypoxic stress tolerance

Sucrose synthase (SUS; EC 2.4.1.13) plays important roles in sugar metabolism and abiotic stress response. But the genes encoding SUS in cucumber (Cucumis sativus L.) have not been well studied. Here, we isolated four cucumber sucrose synthase genes (CsSUS). Among them, CsSUS3, which highly expressed in the roots, was chosen for further study. Immunolocalization and subcellular localization analysis indicated that CsSUS3 localized in the cytosol and the plasma membrane, and mainly existed in the companion cells of phloem in the roots. When suffering hypoxia stress from flooding, CsSUS3 expression and SUS activity in roots increased, especially in the lateral roots; moreover, the soluble SUS activity increased clearly, but the membrane fraction hardly changed. Compared with the wild‐type cucumbers, the transgenic lines with antisense expression of CsSUS3 were more sensitive to flooding. After 6 d of flooding, the SUS activity, soluble sugar and uridine 5′‐diphosphate glucose (UDPG) content and the ratio of ATP/ADP in the roots of transgenic plants were significantly lower than that in wild‐type plants. Moreover, the transgenic lines grew more slowly with more yellow necrosis in the leaves. These findings suggested CsSUS3 participated in resisting hypoxic stress. Furthermore, the mechanism of CsSUS3 in resisting hypoxic stress was also discussed.     

应激颗粒：细胞调控病毒感染的重要策略

真核细胞受到热休克、氧化应激、营养缺乏或者病毒感染等外界压力的刺激下会诱导一系列的应答反应,如形成应激颗粒(stress granule,SG),从而使细胞能更好地适应环境压力。SG作为胞浆中翻译起始复合物的聚集产物,在细胞的基因表达和稳态中发挥着重要的作用。病毒感染是诱导SG形成的条件之一,病毒侵入宿主细胞后会"借用"宿主的翻译机制完成自己的生命周期,宿主为了抵抗病毒的侵略而暂停翻译形成SG。本文对SG的产生及功能,SG与病毒的相互作用以及SG与病毒诱导的先天性免疫的关系等方面进行了综述,以期为进一步研究抗病毒策略提供方向。     

植物WRKY转录因子结构特点及其生物学功能

WRKY转录因子是近年来在植物中发现的N-端含有WRKYGQK高度保守氨基酸序列的新型转录调控因子, 它能够与(T)(T)TGAC(C/T)序列(W-box)发生特异性作用, 调节启动子中含W-box元件的调节基因和/或功能基因的表达, 从而参与植物的各种防卫反应, 调节植物的生长发育等。文章主要论述了植物WRKY转录因子的基本结构及其生物学功能。