Erwinia carotovora ssp. carotovora Infection Induced ＂Defense Lignin＂ Accumulation and Lignin Biosynthetic Gene Expression in Chinese Cabbage （Brassica rapa L. ssp. pekinensis）

Erwinia carotovora subsp, carotovora （Ecc） infects and causes soft rot disease in hundreds of crop species including vegetables, flowers and fruits. Lignin biosynthesis has been implicated in defensive reactions to injury and pathogen infection in plants. In this work, variations of lignin content and gene expression in the molecular interaction between Chinese cabbage and Ecc were investigated. H2O2 accumulation and peroxidase activity were detected by 3, 3＇- Dimethoxybenzidine staining at mocked and Ecc-inoculated sites of Chinese cabbage leafstalks. Klason lignin content in inoculated plants increased by about 7.84%, 40.37%, and 43.13% more than that of the mocked site at 12, 24 and 72 h after inoculation, respectively. Gas chromatography detected more p-coumaryl （H） and less coniferyl （G） and sinapyl （S） monolignins in leafstalks of Chinese cabbage. All three monomers increased in Ecc-infected leafstalks, and the Ecc-induced ＂defense lignin＂ were composed of more G and H monolignins, and less S monolignin. After searching the expressed sequence tags （EST） data of Chinese cabbage, 12 genes putatively encoding enzymes involved in lignin biosynthesis were selected to study their expression. All of these genes could be induced by mock inoculation and Ecc infection, while the gene expression lasted for several more hours in the infected samples than in mocked and untreated plants. Our results indicated that ＂defense lignin＂ was different from the developmental lignin in composition; G and S monolignins were significantly induced in plants in response to the soft rot Ecc; thus, lignin biosynthesis was differentially regulated and played a role in plant response to the soft rot Ecc.     

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route,represented by a metabolic grid for which most of the genes involved have been sequenced in several plants,mainly in the model-plants Arabidopsis thaliana and Populus.Plants are exposed to different stresses,which may change lignin content and composition.In many cases,particularly for plant-microbe interactions,this has been suggested as defence responses of plants to the stress.Thus,understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall.This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.     

Preliminary studies on differential defense responses induced during plant communication

We compared the expression patterns of three representative genes in undamaged tomato and tobacco plants in response to exposure to either tomato or tobacco fed on by Helicoverpa armigera (cotton bollworm). When tomato and tobacco, two species of one family, were incubated in the chambers with the tomato plants damaged by the cotton bollworm, the expression of the PR1, BGL2, and PAL genes was up-regulated in leaves of both plants. However, the levels of gene expression were significantly higher in the tomato than that in the tobacco. In addition, the activities of enzymes, peroxidase, polyphenol oxidase, and lipoxygenase were found to be higher in the tomato than those in the tobacco. Similar results were obtained when the damaged plants were replaced by the tobacco.     

Riboflavin-induced Priming for Pathogen Defense in Arabidopsis thaliana

Riboflavin （vitamin B2） participates in a variety of redox processes that affect plant defense responses. Previously we have shown that riboflavin induces pathogen resistance in the absence of hypersensitive cell death （HCD） in plants. Herein, we report that riboflavin induces priming of defense responses in Arabidopsis thaliana toward infection by virulent Pseudomonas syringae pv. tomato DC3000 （Pst）. Induced resistance was mechanistically connected with the expression of defense response genes and cellular defense events, including H202 burst, HCD, and callose deposition in the plant. Riboflavin treatment and inoculation of plants with Pst were neither active but both synergized to induce defense responses. The priming process needed NPRI （essential regulator of systemic acquired resistance） and maintenance of H202 burst but was independent of salicylic acid, jasmonic acid, ethylene, and abscisic acid. Our results suggest that the role of riboflavin in priming defenses is subject to a signaling process distinct from the known pathways of hormone signal transduction.     

The defense-responsive genes showing enhanced and repressed expression after pathogen infection in rice (Oryza sativa L.)

Despite large numbers of studies about defense response, processes involved in the resistance of plants to incompatible pathogens are still largely uncharacterized. The objective of this study was to identify genes involved in defense response by cDNA array analysis and to gain knowledge about the functions of the genes involved in defense response. Approximately 20000 rice cDNA clones were arrayed on nylon filters. RNA samples isolated from different rice lines after infection with incompatible strains or isolates of Xanthomonas oryzae pv. oryzae or Pyricularia grisea, respectively, were used to synthesize cDNA as probes for screening the cDNA arrays. A total of 100 differentially expressed unique sequences were identified from 5 pathogen-host combinations. Fifty-three sequences were detected as showing enhanced expression and 47 sequences were detected as showing repressed expression after pathogen infection. Sequence analysis revealed that most of the 100 sequences had various degrees of homology with     

Cell Wall Lignin is Polymerised by Class Ⅲ Secretable Plant Peroxidases in Norway Spruce

Class Ⅲ secretable plant peroxidases occur as a large family of genes in plants with many functions and probable redundancy. In this review we are concentrating on the evidence we have on the catalysis of lignin polymerization by class Ⅲ plant peroxidases present in the apoplastic space in the xylem of trees. Some evidence exists on the specificity of peroxidase isozymes in lignin polymerization through substrate specificity studies, from antisense mutants in tobacco and poplar and from tissue and cell culture lines of Norway spruce (Picea abies) and Zinnia elegans. In addition, real time (RT-)PCR results have pointed out that many peroxidases have tissue specific expression patterns in Norway spruce. Through combining information on catalytic properties of the enzymes, on the expression patterns of the corresponding genes, and on the presence of monolignols and hydrogen peroxide in the apoplastic space, we can show that specific peroxidases catalyze lignin polymerization in the apoplastic space of Norway spruce xylem.     

Establishing a gene trap system mediated by T-DNA(GUS) in rice

Two plasmids, p13GUS and p13GUS2, were constructed to create a gene trap system containing the promoterless β-glucuronidase (GUS) reporter gene in the T-DNA region. Transformation of these two plasmids into the rice variety Zhonghua 11 (Oryza sativa ssp. japonica cv.), mediated by Agrobacterium tumefaciens, resulted in 942 independent transgenic lines. Histochemical GUS assays revealed that 31 To plants had various patterns of the reporter gene expression, including expression in only one tissue, and simultaneously in two or more tissues. Hygromycin-resistant (hygr) homozygotes were screened and the copy number of the T-DNA inserts was determined in the GUS-positivs transgenic plants. The flanking sequences of the T-DNA were isolated by inverse-polymerase chain reaction and the insert positions on the rice genome of T-DNA were determined by a basic local alignment search tool in the GUS-positive transgenic plants transformed with plasmid p13GUS. Moreover, calii induced from the seeds of the T1 generation of 911 GUS-negative transgenic lines were subjected to stress and hormone treatments. Histochemical GUS assays were carried out on the calli before and after treatment. The results revealed that calli from 21 lines displayed differential GUS expression after treatment. All of these data demonstrated that this trap system is suitable for identifying rice genes, including those that are sensitive to induction.     

Phenotypic and Genetic Diversity of Erwinia carotovora ssp. carotovora Strains from Asia

A collection of 87 strains of the soft rot pathogen Erwinia carotovora ssp. carotovora (Ecc) isolated from various host plants in Japan, Korea and Thailand was characterized by bacteriological, pathological and genetic properties. On the basis of pathogenicity on the potato, tomato, onion and cucumber, strains were divided into four groups. They were also characterized by PCR‐restriction fragment length polymorphisms (RFLP) of 16S ribosomal DNA (rDNA), 16S‐23S rDNA intergenic spacer regions (ISRs) and a pel gene encoding pectate lyase. By analysis of 16S rDNA RFLP generated by Hinf I, Ecc strains were differentiated into two groups where it was discovered that most strains from Korea and Japan belonged to the same group. In the analysis of ISRs RFLP with MboI, two patterns were found. All Thai strains showed the same pattern. In the analysis of the pel gene RFLP with Sau3AI, all strains were separated into two independent patterns except for one strain. The strain (MAFF 301937) isolated from the mulberry showed a unique RFLP pattern of the pel gene. In cluster analysis based on 26 phenotypic characters, Ecc strains were composed of two groups, A and B. Group A contained typical Ecc strains which provided negative reactions in testing the production of reducing substances from sucrose and acids from α‐methyl glucoside. All Thai strains and most of the Korean strains belonged to group A, whereas group B contained atypical Ecc strains, which were isolated in Japan and Korea; the properties of this group were similar to those of E. carotovora ssp. atroseptica. The research reported here was undertaken to provide information on the strains of E. carotovora ssp. carotovora in Asia.     

拟南芥对细菌性软腐病抗性变异分析

由胡萝卜软腐欧文氏菌胡萝卜软腐亚种 Erwinia carotovora subsp.carotovora （Ecc）引起的细菌性软腐病是世界性的重要流行病害,由于缺乏天然抗源,研究进展缓慢,拟南芥成为软腐病抗性研究的主要试材。本文选用 29 份拟南芥材料,制定了病情分级标准,以接种后 48 小时的病情指数作为软腐病抗性的鉴定指标,筛选出抗软腐病材料 CS906 和感病材料 CS20。通过分析抗、感材料接种 Ecc 后 AOS、ERF1-1、PR1、PDF1.2 和 PAL1 等 5 个基因的表达变化,发现 SA、ET 和 MJ 信号途径都参与了拟南芥对 Ecc 的防卫反应,且基因表达模式在抗、感材料中相似,差异体现在表达量上。本研究对深入探讨拟南芥软腐病抗病机制具有重要意义。     

珠芽魔芋对细菌性软腐病的抗性鉴定研究

采用魔芋Amorphophallus spp.块茎点种、注射、灌根接种及田间调查等方法,对国内普遍栽种的珠芽红魔芋A. bulbifer、珠芽金魔芋A. muelleri、花魔芋A. konjac和白魔芋A. albus等12个种质材料进行抗软腐病鉴定、比较和评价,以分析珠芽魔芋对抗细菌性软腐病的抗病水平。结果表明,供试材料对软腐病抗性差异较大,珠芽金魔芋种质对细菌性软腐病均有免疫性(I),德宏及临沧珠芽红魔芋种质为高抗病品种(HR);缅甸珠芽红魔芋为抗病品种(R);富源花魔芋、楚雄花魔芋、日本农林2号、鄂魔芋1号、秦魔1号、昭通白魔芋、丽江白魔芋均属易感品种(S),与田间抗性调查情况基本相符。     

Erwinia carotovora subsp. carotovora and Erwinia-derived elicitors HrpN and PehA trigger distinct but interacting defense responses and cell death in Arabidopsis

We have used an hrp-positive strain of the soft rot pathogen Erwinia carotovora subsp. carotovora to elucidate plant responses to this bacterial necrotroph. Purified virulence determinants, harpin (HrpN) and polygalacturonase (PehA), were used as tools to facilitate this analysis. We show that HrpN elicits lesion formation in Arabidopsis and tobacco and triggers systemic resistance in Arabidopsis. Establishment of resistance is accompanied by the expression of salicylic acid (SA)-dependent, but also jasmonate/ethylene (JA/ET)-dependent, marker genes PR1 and PDF1.2, respectively, suggesting that both SA-dependent and JA/ET-dependent defense pathways are activated. Use of pathway-specific mutants and transgenic NahG plants show that both pathways are required for the induction of resistance. Arabidopsis plants treated simultaneously with both elictors PehA, known to trigger only JA/ET-dependent defense signaling, and HrpN react with accelerated and enhanced induction of the marker genes PR1 and PDF1.2 both locally and systemically. This mutual amplification of defense gene expression involves both SA-dependent and JA/ET-dependent defense signaling. The two elicitors produced by E. carotovora subsp. carotovora also cooperate in triggering increased production of superoxide and lesion formation.     

大白菜软腐菌种群组成及优势菌致病型的研究

对黑龙江省成熟大白菜[Brassica pekinensis（Lour．）Rupr．]生产田采集的软腐病菌进行分离、纯化,并根据形态学特征分析了大白菜软腐病菌的种群组成。结果表明,引起黑龙江省秋季大白菜软腐病的主要致病菌是胡萝卜软腐欧文氏菌胡萝卜软腐亚种[Erwinia carotovora（Jones）Bergey et al．subsp、carotovora]（Ecc）;利用20个Ecc菌株的混合菌对来源于不同生态型及不同地区的大白菜品种进行接种,筛选出5个鉴别寄主,以此将20个Ecc菌株划分为5个致病力类型,其中V型为优势致病菌,其分布广且致病力强。     

Enumeration of two competing Erwinia carotovora populations in potato tubers by a membrane filter-immunofluorescence procedure

Relative increases in cell populations of specific Erwinia carotovora strains injected into potato tubers either singly or in combination of two strains were determined by depositing tissue extracts on membrane filters and staining cells of individual strains by immunofluorescence. The population increase of an Erw. carotovora subsp. atroseptica (Eca) strain was, in general, not affected by the presence of an Erw. carotovora subsp. carotovora (Ecc) strain. However, the increase of an Ecc strain was inhibited by the presence of an Eca strain, especially at incubation temperatures of 5° and 15°C but not at 26°C. One Ecc strain consistently increased in population over another Ecc strain at a greater rate when they were inoculated together at the same loci in comparison to when they were inoculated separately at different loci.     

接种马铃薯软腐病菌引起的烟草叶片爆发

用马铃薯软腐病菌处理烟草后,以化学法测定了叶片中O-2含量,发现在接种后1～14 h内只出现一次O-2爆发,不同于以往植物悬浮细胞研究中出现的两次爆发结果.接种软腐病菌后2 h和6 h烟草叶片O-2的电子自旋共振波谱图(electron spin resonance,ESR)显示了同样的一次O-2爆发结果.接种后烟草叶片的线粒体和叶绿体O-2爆发与叶片的同步,显示此两种细胞器参与烟草叶片在软腐病菌作用下的O-2发生.无光照叶绿体O-2的ESR谱线不出现,表明叶绿体O-2可能来源于光合电子传递链.马铃薯软腐病菌作用下烟草叶片的O-2爆发是多位点的.