Resistance gene-dependent activation of a calcium-dependent protein kinase in the plant defense response

In the Cf-9/Avr9 gene-for-gene interaction, the Cf-9 resistance gene from tomato confers resistance to the fungal pathogen Cladosporium fulvum, which expresses the corresponding pathogen-derived avirulence product Avr9. To understand R gene function and dissect the signaling mechanisms involved in the induction of plant defenses, we studied Cf-9/Avr9-dependent activation of protein kinases in transgenic Cf9 tobacco cell cultures. Using a modified in-gel kinase assay with histone as substrate, we identified a membrane-bound, calcium-dependent protein kinase (CDPK) that showed a shift in electrophoretic mobility from 68 to 70 kD within 5 min after Avr9 elicitor was added. This transition from the nonelicited to the elicited CDPK form was caused by a phosphorylation event and was verified when antibodies to CDPK were used for protein gel blot analysis. In addition, the interconversion of the corresponding CDPK forms could be induced in vitro in both directions by treatment with either phosphatase or ATP. In vitro protein kinase activity toward syntide-2 or histone with membrane extracts or gel-purified enzyme was dependent on Ca(2)+ content and was compromised by the calmodulin antagonist N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7) but not by its inactive isoform N-(6-aminohexyl)-1-naphthalenesulfonamide. In these assays, the CDPK activity in elicited samples, reflecting predominantly the phosphorylated 70-kD CDPK form, was greater than in nonelicited samples. Thus, Avr9/Cf-9-dependent phosphorylation and subsequent transition from the nonelicited to the elicited form correlate with the activation of a CDPK isoform after in vivo stimulation. Because that transition was not inhibited by W-7, the in vivo CDPK activation probably is not the result of autophosphorylation. Studies with pharmacological inhibitors indicated that the identified CDPK is independent of or is located upstream from a signaling pathway that is required for the Avr9-induced active oxygen species.     

Macroevolution of plant defense strategies

Theories of plant defense expression are typically based on the concepts of tradeoffs among traits and of phylogenetic conservatism within clades. Here, I review recent developments in phylogenetic approaches to understanding the evolution of plant defense strategies and plant-herbivore coevolutionary interactions. I focus particularly on multivariate defense against insect herbivores, which is the simultaneous deployment of multiple traits, often arranged as convergently evolved defense syndromes. Answering many of the outstanding questions in the biology of plant defense will require generating broad hypotheses that can be explicitly tested by using comparative approaches and interpreting phylogenetic patterns. The comparative approach has wide-spread potential to reinvigorate tests of classic hypotheses about the evolution of interspecific interactions.     

Endophage-ectophage ratios and plant defense

Summary Endophagous folivores, which are concealed inside leaf tissue for much of their life cycle, or which live externally but feed internally, should be more successful on heavily defended plants than ectophagous species. This is because endophages are more facile at feeding selectively and can manipulate tissue development to avoid physical and chemical defenses and to enhance nutrition. As a result, endophage-ectophage ratios should increase on more heavily defended hosts. This pattern will likely be strengthened by negative asymmetrical interactions with ectophages and pathogens, which may displace endophages from lightly defended hosts. The hypothesis predicts that endophages should be particularly abundant in resource-poor habitats which seem to support a preponderance of heavily defended hosts. Although data do not yet exist for a rigorous test, several observed cases where endophage distributions seem biased toward heavily defended hosts are at least consistent with the hypothesis. Plant defense levels may have little influence on the total number of herbivores associated with a host, but I suggest that guild structure can be profoundly altered.     

Chemical defense lowers plant competitiveness

Both plant competition and plant defense affect biodiversity and food web dynamics and are central themes in ecology research. The evolutionary pressures determining plant allocation toward defense or competition are not well understood. According to the growth–differentiation balance hypothesis (GDB), the relative importance of herbivory and competition have led to the evolution of plant allocation patterns, with herbivore pressure leading to increased differentiated tissues (defensive traits), and competition pressure leading to resource investment towards cellular division and elongation (growth-related traits). Here, we tested the GDB hypothesis by assessing the competitive response of lima bean (Phaseolus lunatus) plants with quantitatively different levels of cyanogenesis—a constitutive direct, nitrogen-based defense against herbivores. We used high (HC) and low cyanogenic (LC) genotypes in different competition treatments (intra-genotypic, inter-genotypic, interspecific), and in the presence or absence of insect herbivores (Mexican bean beetle, Epilachna varivestis) to quantify vegetative and generative plant parameters (above and belowground biomass as well as seed production). Highly defended HC-plants had significantly lower aboveground biomass and seed production than LC-plants when grown in the absence of herbivores implying significant intrinsic costs of plant cyanogenesis. However, the reduced performance of HC- compared to LC-plants was mitigated in the presence of herbivores. The two plant genotypes exhibited fundamentally different responses to various stresses (competition, herbivory). Our study supports the GDB hypothesis by demonstrating that competition and herbivory affect different plant genotypes differentially and contributes to understanding the causes of variation in defense within a single plant species.     

Impact of phyto-oxylipins in plant defense

Phyto-oxylipins are metabolites produced in plants by the oxidative transformation of unsaturated fatty acids via a series of diverging metabolic pathways. Biochemical dissection and genetic approaches have provided compelling evidence that these oxygenated derivatives actively participate in plant defense mechanisms. During the past decade, interest in this field was focused on the biosynthesis of jasmonic acid (one branch of C18 polyunsaturated fatty acid metabolism) and on its relationship to the other plant defense-signaling pathways. However, recently, antisense strategies have revealed that oxylipins other than jasmonates are probably also essential for the resistance of plants to pathogens.     

植物防御反应的生化调控

在与病原物长期相互影响的共进化过程中 ,植物逐渐形成了一系列复杂而行之有效的保护机制。自 19世纪末发现高等动物体存在抗原 -抗体免疫系统以来 ,曾推测植物在受到病原物侵染后也会产生类似于动物的免疫反应 ,然而在植物中寻找特异性抗体的尝试却以失败而告终。尽管如此 ,Ｃｈｅｓｔｅｒ发现遭受病原物初次侵染而存活下来的植物 ,再次受到侵染时抗病性增强[1] 。约 30年后 ,Ｒｏｓｓ再次描述了这种现象[2 ] ,并将这种现象称之为“全株获得性抗病性 (ｓｙｓｔｅｍｉｃａｃ ｑｕｉｒｅｄｒｅｓｉｓｔａｎｃｅ ,ＳＡＲ)”。ＳＡＲ通常在病原…     

Jasmonate-dependent defense signaling in plant tissues

Depending on the stress type, plants activate various signal transduction pathways inducing the optimum defense process. This review is devoted to jasmonate (JA) dependent signaling involved in plant defense against biotic and abiotic stresses, including those determined by wounding, necrotrophic pathogens, pests, and herbivores. The sequence of major events of JA signaling is discussed. It is noted that JA signaling in plants is incorporated into a complex signaling network.     

植物防卫的碳-养分平衡假说

碳-养分平衡假说(carbon-nutrient balance hypothesis,CNBH)认为,植物组织中次生代谢物浓度受环境碳-资源有效性控制;植物体内次生代谢物按照化学计量的要求进行分配;资源分配给防卫物的必要条件是资源供应量满足植物生长需求后仍过剩。CNBH自提出以来,其适用范围不断受到限制,解释与预测研究结果的能力逐渐显现不足。期间,对CNBH进行过优化和修改,设置了多种限制条件,以期能使CNBH得到补救,继续成为指导植物-草食动物间相互作用和植物体内资源分配的相关理论。然而,随着研究的逐渐深入,CNBH被证实缺乏逻辑性和内在一致性;CNBH不能满足假说本身的发展要求,缺乏明确可行的量化指标体系,也没有明确地标识出理论预测范围与可测试范围之间的界限。研究表明,CNBH的基本假设本身是错误的;随着人们对植物-草食动物间相互作用的认知能力加强,更深刻地认识到资源在植物体内的分配模式,意识到CNBH假说的严重缺陷。在现有的植物防卫理论中,生长-分化平衡假说(growth-differentiation balance hypothesis)较为成熟,不但具有CNBH的优点,而且更具有植物生理学和进化...     

Self-recognition affects plant communication and defense

Animals have the ability to distinguish self from non-self, which has allowed them to evolve immune systems and, in some instances, to act preferentially towards individuals that are genetically identical or related. Self-recognition is less well known for plants, although recent work indicates that physically connected roots recognize self and reduce competitive interactions. Sagebrush uses volatile cues emitted by clipped branches of self or different neighbours to increase resistance to herbivory. Here, we show that plants that received volatile cues from genetically identical cuttings accumulated less natural damage than plants that received cues from non-self cuttings. Volatile communication is required to coordinate systemic processes such as induced resistance and plants respond more effectively to self than non-self cues. This self/non-self discrimination did not require physical contact and is a necessary first step towards possible kin recognition and kin selection.     

Characterization of nuclear factors for elicitor-mediated activation of the promoter of the pea phenylalanine ammonia-lyase gene 1.

The nuclear factors presumably associated with the activation of the gene encoding phenylalanine ammonia-lyase by a fungal elicitor were characterized in pea (Pisum sativum L.) epicotyls. The TATA-proximal region was dissected and putative cis-regulatory elements in the promoter of pea phenylalanine ammonia-lyase gene 1 were examined by gel-mobility shift and in vitro footprinting analyses. Specific binding of the nuclear factors to the promoter-proximal regions of pea phenylalanine ammonia-lyase gene 1 associated with elicitor-mediated activation was detected at a region containing consensus sequence motifs of boxes 2 and 4 and other AT-rich sequences. The analyses of DNA fragments containing the deleted promoter regions suggested that a residue from -183 to -173 (ATTAGTAAGTGAT) was essential for a maximal activity of forming low-mobility complex (LMC) in the gel-mobility shift assay, and synthetic oligonucleotides confirmed the presence of at least one nuclear component associated with the formation of an active LMC. Competition experiments and treatment with Hoechst 33258 provided direct evidence that the formation of LMC with the promoter fragments from genes encoding phenylalanine ammonia-lyase and chalcone synthase in pea contained one or more of the same proteins that recognize AT-rich sequence motifs for binding. It also suggests that common high-mobility group-like proteins might be involved in the regulation of elicitor-inducible genes in pea.     

Antioxidative defense activation in soybean cells

Suspension-cultured, photoheterotrophically grown, green soybean cells ( Glycine max L.) were used to investigate alterations in the cellular contents of ascorbate and glutathione, as well as specific activities of antioxidative enzymes, elicited by salicylic acid (SA) and BTH [benzo(1,2,3)thiadiazole-7-carbothioic acid S -methylester]. Both antioxidants were positively regulated by 48-h incubations with SA and BTH, respectively, the latter induced a stronger increase in antioxidant levels compared to SA. The specific activities of glutathione reductase, monodehydroascorbate reductase and glutathione S -transferase increased strongly in soybean cells as a response to both SA and BTH. The enzyme activations observed were in the range of 2–8-fold. Catalase activity was also increased 2-fold by SA but decreased when cells were incubated with BTH. These results indicate an activation of the cellular antioxidative system at both the antioxidant and enzyme level. In addition, the effects of SA and BTH on phytotoxicity exerted by the peroxidizing herbicide oxyfluorfen were investigated. Both compounds protected soybean cells from herbicide-induced lipid peroxidation in a time- and concentration-dependent manner and strongly suppressed the herbicide-induced accumulation of protoporphyrin IX. SA as well as BTH antagonize the action of peroxidizing herbicides.     

植物对植食性哺乳动物的化学防卫

综述植物次生合物防卫植食性哺乳动物食的研究进展,植物组织的次生化合物主要为酚类、萜类及含N类化合物,植物对动物觅食的化学防卫对策以次生化合物的各类而有差异,次生化合物通过对动物的食物摄入、消化、代谢,以及敏殖活动的效应,以抵御动物的觅食。将植物化学防卫与动物适应对策相结合,探讨动物－植物协同进化模式,是该研究领域的主要发展趋势。     

beta-Glucosidases as detonators of plant chemical defense

Some plant secondary metabolites are classified as phytoanticipins. When plant tissue in which they are present is disrupted, the phytoanticipins are bio-activated by the action of beta-glucosidases. These binary systems--two sets of components that when separated are relatively inert--provide plants with an immediate chemical defense against protruding herbivores and pathogens. This review provides an update on our knowledge of the beta-glucosidases involved in activation of the four major classes of phytoanticipins: cyanogenic glucosides, benzoxazinoid glucosides, avenacosides and glucosinolates. New aspects of the role of specific proteins that either control oligomerization of the beta-glucosidases or modulate their product specificity are discussed in an evolutionary perspective.