Priming in plant-pathogen interactions

Plants can acquire enhanced resistance to pathogens after treatment with necrotizing attackers, nonpathogenic root-colonizing pseudomonads, salicylic acid, beta-aminobutyric acid and many other natural or synthetic compounds. The induced resistance is often associated with an enhanced capacity to mobilize infection-induced cellular defence responses - a process called 'priming'. Although the phenomenon has been known for years, most progress in our understanding of priming has been made only recently. These studies show that priming often depends on the induced disease resistance key regulator NPR1 (also known as NIM1 or SAI1) and that priming has a major effect on the regulation of cellular plant defence responses.     

Recognition and response in plant-pathogen interactions

Most plants are resistant to the majority of pathogens. Susceptibility is the exception to the more common state of resistance, i.e., being refractory to infection. However, plant pathogens cause serious economic losses by reducing crop yield and quality. Although such organisms are relatively simple genetic entities, in plants, the mechanisms underlying the generation of disease symptoms and resistance responses are complex and, often, unknown. The study of genes associated with plant-pathogen resistance addresses fundamental questions about the molecular, biochemical, cellular, and physiological means of these interactions. Over the past 10 years, the cloning and analysis of numerous plant resistance genes has led researchers to formulate unifying theories about resistance and susceptibility, and the co-evolution of plant pathogens and their hosts. In this review, we discuss the identification of response genes that have been characterized at the molecular level, as well as their putative links to various signaling pathways. We also summarize the knowledge regarding crosstalk among signaling pathways and plant resistance genes.     

Nitric oxide signaling in plant-pathogen interactions

Nitric oxide (NO), first characterized as an endothelium-derived relaxation factor, is involved in diverse cellular processes including neuronal signaling, blood pressure homeostasis, and immune response. Recent studies have also revealed a role for NO as a signaling molecule in plants. As a developmental regulator, NO promotes germination, leaf extension and root growth, and delays leaf senescence and fruit maturation. Moreover, NO acts as a key signal in plant resistance to incompatible pathogens by triggering resistance-associated hypersensitive cell death. In addition, NO activates the expression of several defense genes (e.g. pathogenesis-related genes, phenylalanine ammonialyase, chalcone synthase) and could play a role in pathways leading to systemic acquired resistance.     

Predicting co-complexed protein pairs using genomic and proteomic data integration

Background  

Identifying all protein-protein interactions in an organism is a major objective of proteomics. A related goal is to know which protein pairs are present in the same protein complex. High-throughput methods such as yeast two-hybrid (Y2H) and affinity purification coupled with mass spectrometry (APMS) have been used to detect interacting proteins on a genomic scale. However, both Y2H and APMS methods have substantial false-positive rates. Aside from high-throughput interaction screens, other gene- or protein-pair characteristics may also be informative of physical interaction. Therefore it is desirable to integrate multiple datasets and utilize their different predictive value for more accurate prediction of co-complexed relationship.     

植物与病原微生物互作分子基础的研究进展

植物在与病原微生物共同进化过程中形成了复杂的免疫防卫体系。植物的先天免疫系统可大致分为两个层面。第一个层面的免疫基于细胞表面的模式识别受体对病原物相关分子模式的识别,该免疫过程被称为病原物相关分子模式触发的免疫(PAMP-triggered immunity,PTI),能帮助植物抵抗大部分病原微生物;第二个层面的免疫起始于细胞内部,主要依靠抗病基因编码的蛋白产物直接或间接识别病原微生物分泌的效应子并且激发防卫反应,来抵抗那些能够利用效应子抑制第一层面免疫的病原微生物,这一过程被称为效应子触发的免疫(Effector-triggered immunity,ETI)。这两个层面的免疫都是基于植物对"自我"及"非我"的识别,依靠MAPK级联等信号网络,将识别结果传递到细胞核内,调控相应基因的表达,做出适当的免疫应答。本文着重阐述了植物与病原微生物互作过程中不同层面的免疫反应所发生主要事件的分子基础及研究进展。     

The role of abscisic acid in plant-pathogen interactions

The effect of the abiotic stress hormone abscisic acid on plant disease resistance is a neglected field of research. With few exceptions, abscisic acid has been considered a negative regulator of disease resistance. This negative effect appears to be due to the interference of abscisic acid with biotic stress signaling that is regulated by salicylic acid, jasmonic acid and ethylene, and to an additional effect of ABA on shared components of stress signaling. However, recent research shows that abscisic acid can also be implicated in increasing the resistance of plants towards pathogens via its positive effect on callose deposition.     

Evolution of resistance and virulence in plant-herbivore and plant-pathogen interactions

Herbivores and pathogens often attack or infect the same plant parts, and the same plant traits can affect the likelihood and degree of damage. Research on plant-herbivore and plant-pathogen interactions in natural systems have, however, proceeded largely independently of each other. Our understanding of both types of plant-enemy interaction would be enhanced by greater exposure of researchers to developments in both disciplines and by more studies of interactions between pathogen and herbivore species associated with the same hosts.     

Towards the molecular dissection of fertilization signaling: Our functional genomic/proteomic strategies

Recent advances in DNA sequencing techniques and automated informatics has led to clarification of all genome sequence of some model organisms in a very short period. The demonstration of the first draft sequence of the human genome has prompted us to elaborate new approaches in biology, pharmacology and medicine. Such new research will focus on high throughput methods to function on collections of genes, and hopefully, on a genome-wide, quantitative modeling of the cell system as a whole. In this review article, we discuss the present status of "post genome sequencing" approaches in line with our strategies for understanding the molecular mechanism of fertilization and activation of development using the African clawed frog, Xenopus laevis, as a model system.     

Network analysis of epidermal growth factor signaling using integrated genomic, proteomic and phosphorylation data

To understand how integration of multiple data types can help decipher cellular responses at the systems level, we analyzed the mitogenic response of human mammary epithelial cells to epidermal growth factor (EGF) using whole genome microarrays, mass spectrometry-based proteomics and large-scale western blots with over 1000 antibodies. A time course analysis revealed significant differences in the expression of 3172 genes and 596 proteins, including protein phosphorylation changes measured by western blot. Integration of these disparate data types showed that each contributed qualitatively different components to the observed cell response to EGF and that varying degrees of concordance in gene expression and protein abundance measurements could be linked to specific biological processes. Networks inferred from individual data types were relatively limited, whereas networks derived from the integrated data recapitulated the known major cellular responses to EGF and exhibited more highly connected signaling nodes than networks derived from any individual dataset. While cell cycle regulatory pathways were altered as anticipated, we found the most robust response to mitogenic concentrations of EGF was induction of matrix metalloprotease cascades, highlighting the importance of the EGFR system as a regulator of the extracellular environment. These results demonstrate the value of integrating multiple levels of biological information to more accurately reconstruct networks of cellular response.     

Profiling expression of lipoxygenase in cucumber during compatible and incompatible plant-pathogen interactions

We compared lipoxygenase (LOX) expression in cucumber in response to host and non-host pathogens. Our results displayed significant difference in expression of LOX between compatible and incompatible interaction at 12, 24 and 48 h after inoculation. Moreover, LOX expression at 72 h after inoculation was similar in both compatible and incompatible interaction. It seems that early induction of LOX plays a crucial role in plant defense against pathogens.     

Polygalacturonases, polygalacturonase-inhibiting proteins and pectic oligomers in plant-pathogen interactions

Polygalacturonases (PGs) are produced by fungal pathogens during early plant infection and are believed to be important pathogenicity factors. Polygalacturonase-inhibiting proteins (PGIPs) are plant defense proteins which reduce the hydrolytic activity of endoPGs and favor the accumulation of long-chain oligogalacturonides (OGs) which are elicitors of a variety of defense responses. PGIPs belong to the superfamily of leucine reach repeat (LRR) proteins which also include the products of several plant resistance genes. A number of evidence demonstrates that PGIPs efficiently inhibit fungal invasion.     

Plant integrity: An important factor in plant-pathogen interactions

The effect of plant integrity and of aboveground-belowground defense signaling on plant resistance against pathogens and herbivores is emerging as a subject of scientific research. There is increasing evidence that plant defense responses to pathogen infection differ between whole intact plants and detached leaves. Studies have revealed the importance of aboveground-belowground defense signaling for plant defenses against herbivores, while our studies have uncovered that the roots as well as the plant integrity are important for the resistance of the potato cultivar Sarpo Mira against the hemibiotrophic oomycete pathogen Phytophthora infestans. Furthermore, in the Sarpo Mira–P. infestans interactions, the plant’s meristems, the stalks or both, seem to be associated with the development of the hypersensitive response and both the plant’s roots and shoots contain antimicrobial compounds when the aerial parts of the plants are infected. Here, we present a short overview of the evidence indicating the importance of plant integrity on plant defense responses.     

Genetic elucidation of nitric oxide signaling in incompatible plant-pathogen interactions

Recent experiments indicate that nitric oxide (NO) plays a pivotal role in disease resistance and several other physiological processes in plants. However, most of the current information about the function of NO in plants is based on pharmacological studies, and additional approaches are therefore required to ascertain the role of NO as an important signaling molecule in plants. We have expressed a bacterial nitric oxide dioxygenase (NOD) in Arabidopsis plants and/or avirulent Pseudomonas syringae pv tomato to study incompatible plant-pathogen interactions impaired in NO signaling. NOD expression in transgenic Arabidopsis resulted in decreased NO levels in planta and attenuated a pathogen-induced NO burst. Moreover, NOD expression in plant cells had very similar effects on plant defenses compared to NOD expression in avirulent Pseudomonas. The defense responses most affected by NO reduction during the incompatible interaction were decreased H(2)O(2) levels during the oxidative burst and a blockage of Phe ammonia lyase expression, the key enzyme in the general phenylpropanoid pathway. Expression of the NOD furthermore blocked UV light-induced Phe ammonia lyase and chalcone synthase gene expression, indicating a general signaling function of NO in the activation of the phenylpropanoid pathway. NO possibly functions in incompatible plant-pathogen interactions by inhibiting the plant antioxidative machinery, and thereby ensuring locally prolonged H(2)O(2) levels. Additionally, albeit to a lesser extent, we observed decreases in salicylic acid production, a diminished development of hypersensitive cell death, and a delay in pathogenesis-related protein 1 expression during these NO-deficient plant-pathogen interactions. Therefore, this genetic approach confirms that NO is an important regulatory component in the signaling network of plant defense responses.     

Computational models in plant-pathogen interactions: the case of Phytophthora infestans

Background  

Phytophthora infestans is a devastating oomycete pathogen of potato production worldwide. This review explores the use of computational models for studying the molecular interactions between P. infestans and one of its hosts, Solanum tuberosum.     

Cyclin a-CDK phosphorylation regulates MDM2 protein interactions

The product of the MDM2 gene interacts with and regulates a number of proteins, in particular the tumor suppressor p53. The MDM2 protein is likely to be extensively modified in vivo, and such modification may regulate its functions in cells. We identified a potential cyclin-dependent kinase (CDK) site in murine MDM2, and found the protein to be efficiently phosphorylated in vitro by cyclin A-containing complexes (cyclin A-CDK2 and cyclin A-CDK1), but MDM2 was either weakly or not phosphorylated by other cyclin-containing complexes. Moreover, a peptide containing a putative MDM2 cyclin recognition motif specifically inhibited phosphorylation by cyclin A-CDK2. The site of cyclin A-CDK2 phosphorylation was identified as Thr-216 by two-dimensional phosphopeptide mapping and mutational analysis. Phosphorylation of MDM2 at Thr-216 both weakens its interaction with p53 and modestly augments its binding to p19(ARF). Interestingly, an MDM2-specific monoclonal antibody, SMP14, cannot recognize MDM2 phosphorylated at Thr-216. Changes in SMP14 reactivity of MDM2 in staged cell extracts indicate that phosphorylation of MDM2 at Thr-216 in vivo is most prevalent at the onset of S phase when cyclin A first becomes detectable.