Metabolic regulation of leaf senescence: interactions of sugar signalling with biotic and abiotic stress responses

Sugars are important signals in the regulation of plant metabolism and development. During stress and in senescing leaves, sugars often accumulate. In addition, both sugar accumulation and stress can induce leaf senescence. Infection by bacterial and fungal pathogens and attack by herbivores and gall-forming insects may influence leaf senescence via modulation of the sugar status, either by directly affecting primary carbon metabolism or by regulating steady state levels of plant hormones. Many types of biotic interactions involve the induction of extracellular invertase as the key enzyme of an apoplasmic phloem unloading pathway, resulting in a sourcesink transition and an increased hexose/sucrose ratio. Induction of the levels of the phytohormones ethylene and jasmonate in biotic interactions results in accelerated senescence, whereas an increase in plant- or pathogen-derived cytokinins delays senescence and results in the formation of green islands within senescing leaves. Interactions between sugar and hormone signalling also play a role in response to abiotic stress. For example, interactions between sugar and abscisic acid (ABA) signalling may be responsible for the induction of senescence during drought stress. Cold treatment, on the other hand, can result in delayed senescence, despite sugar and ABA accumulation. Moreover, natural variation can be found in senescence regulation by sugars and in response to stress: in response to drought stress, both drought escape and dehydration avoidance strategies have been described in different Arabidopsis accessions. The regulation of senescence by sugars may be key to these different strategies in response to stress.     

Genome-wide analysis of lysine catabolism in bacteria reveals new connections with osmotic stress resistance

Lysine is catabolized via the saccharopine pathway in plants and mammals. In this pathway, lysine is converted to α-aminoadipic-δ-semialdehyde (AASA) by lysine-ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH); thereafter, AASA is converted to aminoadipic acid (AAA) by α-aminoadipic-δ-semialdehyde dehydrogenase (AASADH). Here, we investigate the occurrence, genomic organization and functional role of lysine catabolic pathways among prokaryotes. Surprisingly, only 27 species of the 1478 analyzed contain the lkr and sdh genes, whereas 323 species contain aasadh orthologs. A sdh-related gene, identified in 159 organisms, was frequently found contiguously to an aasadh gene. This gene, annotated as lysine dehydrogenase (lysdh), encodes LYSDH an enzyme that directly converts lysine to AASA. Pipecolate oxidase (PIPOX) and lysine-6-aminotransferase (LAT), that converts lysine to AASA, were also found associated with aasadh. Interestingly, many lysdh–aasadh–containing organisms live under hyperosmotic stress. To test the role of the lysine-to-AASA pathways in the bacterial stress response, we subjected Silicibacter pomeroyi to salt stress. All but lkr, sdh, lysdh and aasadh were upregulated under salt stress conditions. In addition, lysine-supplemented culture medium increased the growth rate of S. pomeroyi under high-salt conditions and induced high-level expression of the lysdh–aasadh operon. Finally, transformation of Escherichia coli with the S. pomeroyi lysdh–aasadh operon resulted in increased salt tolerance. The transformed E. coli accumulated high levels of the compatible solute pipecolate, which may account for the salt resistance. These findings suggest that the lysine-to-AASA pathways identified in this work may have a broad evolutionary importance in osmotic stress resistance.     

机械损伤对Bt玉米化学防御的系统诱导效应

植物在生长过程中形成了抵御机械损伤等外界胁迫的直接和间接防御体系, 并具有明显的系统性特征。Bt (Bacillus thuringiensis)玉米(Zea mays)是全球商品化最快的抗虫转基因作物之一。机械损伤等外界胁迫对Bt玉米和常规玉米化学防御的系统诱导效应是否存在差异是值得探讨的问题。该文以两个不同转化事件的Bt玉米‘5422Bt1’(Bt11)和‘5422CBCL’(Mon810)以及它们共同的同源常规玉米‘5422’幼苗为材料, 对玉米第一叶进行机械损伤处理6 h后, 检测非损伤部位(第二叶和根系)中Bt蛋白含量、直接防御物质丁布(DIMBDA)含量及其调控基因(Bx1、Bx6和Bx9)表达、直接防御物质总酚含量及其调控基因(PAL)表达、直接防御蛋白调控基因(MPI和PR-2a)表达以及间接防御物质挥发物调控基因(FPS和TPS)表达的变化。结果表明, 与健康植株相比, 机械损伤对两个Bt玉米第二叶和根系的Bt蛋白含量均没有显著影响; 机械损伤第一叶只能系统诱导常规玉米‘5422’第二叶中PAL、TPS和根系中PAL、FPS基因的表达, 使得第二叶丁布含量显著增加, 但根中丁布含量及其调控基因Bx6和Bx9基因的表达量明显下降; 而机械损伤能系统诱导Bt玉米‘5422Bt1’第二叶中Bx6、PAL、PR-2a、TPS和根系中Bx6、Bx9、PAL、MPI、PR-2a、TPS基因的表达, 使得第二叶丁布含量明显增加; 对于另一Bt玉米‘5422CBCL’而言, 机械损伤能系统诱导第二叶中Bx9、PAL、PR-2a、TPS和根系中Bx6、PAL、MPI、TPS基因的表达, 使得根系的总酚含量显著增加。由此可见, 机械损伤对两个Bt玉米化学防御反应的系统诱导作用均强于常规玉米‘5422’, 说明在机械损伤的系统诱导防御过程中, 人工导入抗性(Bt基因)与自身化学防御过程之间的互作关系是协同的。     

Isolation and characterization of resistance and defense gene analogs in cotton (Gossypium barbadense L.)

Plant disease resistance gene (R gene) and defense response gene encode some conserved motifs. In the present work, a PCR strategy was used to clone resistance gene analogs (RGAs) and defense gene analogs (DGAs) from Sea-island cotton variety Hai7124 using oligonucleotide primers based on the nucleotide-binding site (NBS) and serine/threonine kinase (STK) in the R-gene and pathogenesis-related proteins of class 2 (PR2) of defense response gene. 79 NBS sequences, 21 STK sequences and 11 DGAs were cloned from disease-resistance cotton. Phylogenic analysis of 79 NBS-RGAs and NBS-RGAs nucleotide sequences of cotton already deposited in GenBank identified one new sub-cluster. The deduced amino acid sequences of NBS-RGAs and STK-RGAs were divided into two distinct groups respectively: Toll/Interleukin-1 receptor (TIR) group and non-TIR group, A group and B group. The expression of RGAs and DGAs having consecutive open reading frame (ORF) was also investigated and it was found that 6 NBS-RGAs and 1 STK-RGA were induced, and 1 DGA was up-regulated by infection of Verticillium dahliae strain VD8. 4 TIR-NBS-RGAs and 4 non-TIR-NBS-RGAs were arbitrarily used as probes for Southern-blotting. There existed 2–10 blotted bands. In addition, since three non-TIR-NBS-RGAs have the same hybridization pattern, we conjecture that these three RGAs form a cluster distribution in the genome.     

Isolation and characterization of resistance and defense gene analogs in cotton (Gossypium barbadense L.)

Plant disease resistance gene (R gene) and defense response gene encode some con-served motifs. In the present work,a PCR strategy was used to clone resistance gene analogs (RGAs) and defense gene analogs (DGAs) from Sea-island cotton variety Hai7124 using oligonucleotide primers based on the nucleotide-binding site (NBS) and serine/threonine kinase (STK) in the R-gene and pathogenesis-related proteins of class 2 (PR2) of defense response gene. 79 NBS sequences,21 STK sequences and 11 DGAs were cloned from disease-resistance cotton. Phylogenic analysis of 79 NBS-RGAs and NBS-RGAs nucleotide sequences of cotton already deposited in GenBank identified one new sub-cluster. The deduced amino acid sequences of NBS-RGAs and STK-RGAs were divided into two distinct groups respectively: Toll/Interleukin-1 receptor (TIR) group and non-TIR group,A group and B group. The expression of RGAs and DGAs having consecutive open reading frame (ORF) was also investigated and it was found that 6 NBS-RGAs and 1 STK-RGA were induced,and 1 DGA was up-regulated by infection of Verticillium dahliae strain VD8. 4 TIR-NBS-RGAs and 4 non-TIR-NBS-RGAs were arbitrarily used as probes for Southern-blotting. There existed 2-10 blotted bands. In addition,since three non-TIR-NBS-RGAs have the same hybridization pattern,we conjecture that these three RGAs form a cluster distribution in the genome.     

Isolation and characterization of resistance and defense gene analogs in cotton (Gossypium barbadense L.)

Plant disease resistance gene (R gene) and defense response gene encode some conserved motifs. In the present work, a PCR strategy was used to clone resistance gene analogs (RGAs) and defense gene analogs (DGAs) from Sea-island cotton variety Hai7124 using oligonucleotide primers based on the nucleotide-binding site (NBS) and serine/threonine kinase (STK) in the R-gene and pathogenesis-related proteins of class 2 (PR2) of defense response gene. 79 NBS sequences, 21 STK sequences and 11 DGAs were cloned from disease-resistance cotton. Phylogenic analysis of 79 NBS-RGAs and NBS-RGAs nucleotide sequences of cotton already deposited in GenBank identified one new sub-cluster. The deduced amino acid sequences of NBS-RGAs and STK-RGAs were divided into two distinct groups respectively: Toll/Interleukin-1 receptor (TIR) group and non-TIR group, A group and B group. The expression of RGAs and DGAs having consecutive open reading frame (ORF) was also investigated and it was found that 6 NBS-RGAs and 1 STK-RGA were induced, and 1 DGA was up-regulated by infection of Verticillium dahliae strain VD8. 4 TIR-NBS-RGAs and 4 non-TIR-NBS-RGAs were arbitrarily used as probes for Southern-blotting. There existed 2–10 blotted bands. In addition, since three non-TIR-NBS-RGAs have the same hybridization pattern, we conjecture that these three RGAs form a cluster distribution in the genome.     

不同浓度氯化钙浸种处理对水稻防御酶活性和抗褐飞虱的影响

[目的]研究不同浓度氯化钙(calcium chloride,CaCl2)浸种处理对水稻防御酶活性和抗褐飞虱Nilaparvata lugens的影响.[方法]分别用10,20,30,40和50 mmol/L CaCl2溶液浸泡水稻种子48 h,以蒸馏水浸种为对照,待水稻长至分蘖期时,检测褐飞虱3龄若虫取食胁迫下各浓度...     

Arabidopsis GH3-LIKE DEFENSE GENE 1 is required for accumulation of salicylic acid, activation of defense responses and resistance to Pseudomonas syringae

In Arabidopsis, the GH3-like gene family consists of 19 members, several of which have been shown to adenylate the plant hormones jasmonic acid, indole acetic acid and salicylic acid (SA). In some cases, this adenylation has been shown to catalyze hormone conjugation to amino acids. Here we report molecular characterization of the GH3-LIKE DEFENSE GENE 1 (GDG1), a member of the GH3-like gene family, and show that GDG1 is an important component of SA-mediated defense against the bacterial pathogen Pseudomonas syringae. Expression of GDG1 is induced earlier and to a higher level in response to avirulent pathogens compared to virulent pathogens. gdg1 null mutants are compromised in several pathogen defense responses, including activation of defense genes and resistance against virulent and avirulent bacterial pathogens. Accumulation of free and glucoside-conjugated SA (SAG) in response to pathogen infection is compromised in gdg1 mutants. All defense-related phenotypes of gdg1 can be rescued by external application of SA, suggesting that gdg1 mutants are defective in the SA-mediated defense pathway(s) and that GDG1 functions upstream of SA. Our results suggest that GDG1 contributes to both basal and resistance gene-mediated inducible defenses against P. syringae (and possibly other pathogens) by playing a critical role in regulating the levels of pathogen-inducible SA. GDG1 is allelic to the PBS3 (avrPphB susceptible) gene.     

Characterization of an Arabidopsis–Phytophthora Pathosystem: resistance requires a functional PAD2 gene and is independent of salicylic acid, ethylene and jasmonic acid signalling

Arabidopsis accessions were screened with isolates of Phytophthora porri originally isolated from other crucifer species. The described Arabidopsis-Phytophthora pathosystem shows the characteristics of a facultative biotrophic interaction similar to that seen in agronomically important diseases caused by Phytophthora species. In susceptible accessions, extensive colonization of the host tissue occurred and sexual and asexual spores were formed. In incompatible combinations, the plants reacted with a hypersensitive response (HR) and the formation of papillae at the sites of attempted penetration. Defence pathway mutants such as jar1 (jasmonic acid-insensitive), etr1 (ethylene receptor mutant) and ein2 (ethylene-insensitive) remained resistant towards P. porri. However, pad2, a mutant with reduced production of the phytoalexin camalexin, was hyper-susceptible. The accumulation of salicylic acid (SA) and PR1 protein was strongly reduced in pad2. Surprisingly, this lack of SA accumulation does not appear to be the cause of the hyper-susceptibility because interference with SA signalling in nahG plants or sid2 or npr1 mutants had only a minor effect on resistance. In addition, the functional SA analogue benzothiadiazol (BTH) did not induce resistance in susceptible plants including pad2. Similarly, the complete blockage of camalexin biosynthesis in pad3 did not cause susceptibility. Resistance of Arabidopsis against P. porri appears to depend on unknown defence mechanisms that are under the control of PAD2.     

不同辣椒品种抗（耐）西花蓟马的初步筛选及苗期防御酶的变化

【背景】西花蓟马自2003年传入我国以来,呈扩张趋势。辣椒上西花蓟马以化学防治为主,国内尚无抗性资源保护、抗（耐）虫性资源筛选等相关研究。【方法】以20个辣椒品种和西花蓟马为材料,采用幼苗接虫法,根据危害症状分级,计算为害指数并作为抗（耐）评价指标,然后测定不同抗（耐）材料苗期受西花蓟马危害后防御酶活性的变化,探讨其与抗性的关系。【结果】在20个供试辣椒品种中,湘研13号和博辣4号对西花蓟马的抗性较强,其他品种抗性较差,兴蔬绿剑抗性最差;不同辣椒品种抗（耐）虫性与过氧化物酶变化呈正相关,但与过氧化氢酶相关性不显著。【结论与意义】本研究建立了辣椒抗（耐）西花蓟马的筛选评价体系,为挖掘抗西花蓟马的种质资源和西花蓟马的有效防控提供了依据。     

Role of defense enzymes and phenolics in resistance of wheat crop (Triticum aestivum L.) towards aphid complex

Herbivory damage leads to induction of rapid signals and responses in plants such as oxidative burst, accumulation of secondary metabolites and defensive proteins. Response of various defensive enzymes and secondary metabolites in flag leaf samples of six bread wheat varieties against aphid feeding was investigated. Six bread wheat varieties, namely PBW 621 and HD 2967 (timely sown irrigated), PBW 590 and PBW 658 (late sown irrigated), and PBW 644 and PBW 660 (timely sown rainfed) were grown under the aphid infested and uninfested conditions and were sampled at a regular interval to analyze the biochemical changes caused by aphid feeding. A tremendous increase in the overall activity of various enzymes namely superoxide dismutase, glutathione reductase, phenylalanine ammonia lyase and polyphenol oxidase was observed, all of which play an important role in plants defense towards aphid feeding. Each wheat genotype showed an overall difference in their defensive activity towards aphid feeding. However, certain genotypes under different conditions showed significantly less susceptibility towards aphid damage.

Abbreviations: GR: glutathione reductase; HPR: host plant resistance; PAL: phenylalanine ammonia lyase; PPO: poly phenol oxidase; POD: peroxidase; SOD: superoxide dismutase     

The effect of methyl salicylate on the induction of direct and indirect plant defense mechanisms in poplar (Populus × euramericana ‘Nanlin 895’)

The objective of this study was to investigate the effect of different concentrations of methyl salicylate (MeSA) on direct defense and indirect defense in poplar cuttings (Populus × euramericana ‘Nanlin 895’). Four defense-related enzyme activities, such as superoxide dismutase (SOD, EC1.15.1.1), oxydoreductases peroxidase (POD, EC1.11.1.7), catalase (CAT, EC1.11.1.6), and polyphenol oxidase (PPO, EC 1.14.18.1), were measured. The results showed that the SOD activities were induced by 1.0 and 10.0 mM MeSA and the POD activities were induced by MeSA. The CAT activity was induced at low concentrations of MeSA but was inhibited by high concentrations, and the PPO activity was affected by 0.1, 1.0, and 10.0 mM MeSA. Furthermore, the volatiles were detected using gas chromatography–mass spectrometry and gas chromatography. Twenty-one volatile compounds were tentatively identified in the emissions from plant leaves. Of these volatile compounds, (Z)-3-hexen-1-ol and cis-3-hexenyl acetate emissions were the highest. (Z)-3-Nonen-1-ol, (E)-2-hexen-1-ol, 1-octanol, (E,Z)-3,6-nonadien-1-ol, β-ionone, and hexadecanamide were six compounds that were only produced after treatment by 10.0 mM MeSA. These results showed that direct and indirect defense mechanisms in poplars were induced by MeSA.