Molecular Diversity and Assessment of Biological Characteristics of Greek Colletotrichum lindemuthianum Populations

Colletotrichum lindemuthianum  isolates collected in Greece were characterized by the temperature effect on their biological characteristics (mycelial growth, sporulation and spore germinability) and by molecular diversity revealed by RAM and ERIC–BOX PCR analysis. The temperature effect on the assessed biological characteristics resulted in a similar classification according to the origin and virulence patterns of isolates. Colletotrichum lindemuthianum isolates originating from the areas of Nevrokopi and Vrodou showed better adaptation at the lower temperatures exposure (12 and 18°C) compared to isolates originating from the Municipality of Hrisoupolis, which showed better adaptation at the highest temperature tested (24°C). Molecular diversity was detected using RAM and ERIC–BOX PCR primers. Both methods revealed, in a similar way ( r  = 0.58, P = 0.05), two main clusters of isolates, in agreement with previous findings using RAPD and RFLP analysis. The majority of the tested isolates were grouped in the same main cluster (29 out of 35 Greek isolates for both methods) underlying high levels of genotypic similarities between Greek populations of C. lindemuthianum . This study, an extension of previous research, provides further information on population diversity of C. lindemuthianum required for developing more efficient control strategies of bean anthracnose disease.     

Live-cell imaging of conidial fusion in the bean pathogen, Colletotrichum lindemuthianum

Fusion of conidia and conidial germlings by means of conidial anastomosis tubes (CATs) is a common phenomenon in filamentous fungi, including many plant pathogens. It has a number of different roles, and has been speculated to facilitate parasexual recombination and horizontal gene transfer between species. The bean pathogen Colletotrichum lindemuthianum naturally undergoes CAT fusion on the host surface and within asexual fruiting bodies in anthracnose lesions on its host. It has not been previously possible to analyze the whole process of CAT fusion in this or any other pathogen using live-cell imaging techniques. Here we report the development of a robust protocol for doing this with C. lindemuthianum in vitro. The percentage of conidial germination and CAT fusion was found to be dependent on culture age, media and the fungal strain used. Increased CAT fusion was correlated with reduced germ tube formation. We show time-lapse imaging of the whole process of CAT fusion in C. lindemuthianum for the first time and monitored nuclear migration through fused CATs using nuclei labelled with GFP. CAT fusion in this pathogen was found to exhibit significant differences to that in the model system Neurospora crassa. In contrast to N. crassa, CAT fusion in C. lindemuthianum is inhibited by nutrients (it only occurs in water) and the process takes considerably longer.     

Use of green fluorescent protein to detect expression of an endopolygalacturonase gene of Colletotrichum lindemuthianum during bean infection

The 5' noncoding region of clpg2, an endopolygalacturonase gene of the bean pathogen Colletotrichum lindemuthianum, was fused to the coding sequence of a gene encoding a green fluorescent protein (GFP), and the construct was introduced into the fungal genome. Detection of GFP accumulation by fluorescence microscopy examination revealed that clpg2 was expressed at the early stages of germination of the conidia and during appressorium formation both in vitro and on the host plant.     

Detection of the biocontrol agent Colletotrichum coccodes (183088) from the target weed velvetleaf and from soil by strain-specific PCR markers

Diagnostic molecular markers, generated from random amplified polymorphic DNA (RAPD) and used in polymerase chain reaction (PCR), were developed to selectively recognize and detect the presence of a single strain of the biocontrol fungus Colletotrichum coccodes (183088) on the target weed species Abutilon theophrasti and from soil samples. Several isolates of C. coccodes, 15 species of Colletotrichum, a variety of heterogeneous organisms and various plant species were first screened by RAPD-PCR, and a strain specific marker was identified for C. coccodes (183088). No significant sequence similarity was found between this marker and any other sequences in the databases. The marker was converted into a sequence-characterised amplified region (SCAR), and specific primer sets (N5F/N5R, N5Fi/N5Ri) were designed for use in PCR detection assays. The primer sets N5F/N5R and N5Fi/N5Ri each amplified a single product of 617 and 380 bp, respectively, with DNA isolated from strain 183088. The specificity of the primers was confirmed by the absence of amplified products with DNA from other C. coccodes isolates, other species representing 15 phylogenetic groups of the genus Colletotrichum and 11 other organisms. The SCAR primers (N5F/N5R) were successfully used to detect strain 183088 from infected velvetleaf plants but not from seeded greenhouse soil substrate or from soil samples originating from deliberate-released field experiments. The sensitivity of the assay was substantially increased 1000-fold when nested primers (N5Fi/N5Ri) were used in a second PCR run. N5Fi/N5Ri selectively detected strain 183088 from seeded greenhouse soils as well as from deliberate-released field soil samples without any cross-amplification with other soil microorganisms. This rapid PCR assay allows an accurate detection of C. coccodes strain 183088 among a background of soil microorganisms and will be useful for monitoring the biocontrol when released into natural field soils.     

菜豆炭疽菌有性态研究

在引起菜豆炭疽病的 Colletotrichum lindemuthianum (Sacc. Et Magn．)Br. EtCav．大量培养物中,发现一个在低温培养保存中丧失产生分生孢子能力而仅产生子囊壳的菌系。对其形态学、培养特征、单子囊孢子培养的研究及与有关种的形态比较结果表明,这个源于分生孢子的子囊菌培养物是菜豆小丛壳Glomerella lindemuthianum Shear。这个培养物经人工接种菜豆,再分离时首先产生无性态分生孢子,经数代培养又回复有性态,表明有性过程的产生是同宗配合的。这种有性与无性阶段之间的交替和联系,证明这是一个全型态真菌,即菜豆小丛壳 G. lindemuthianum 是无性态荣豆炭疽菌C．Lindemuthianum 的有性态。     

Stimulation of de novo synthesis of L-phenylalanine ammonia-lyase in relation to phytoalexin accumulation in Colletotrichum lindemuthianum elicitor-treated cell suspension cultures of french bean (Phaseolus vulgaris).

(1) The regulation of the accumulation of the isoflavonoid-derived phytoalexin phaseollin in cell suspension cultures of Dwarf French Bean (Phaseolus vulgaris/ has been investigated. (2) An elicitor preparation from cell walls of Colletotrichum lindemuthianum, the causal agent of anthracnose disease of French bean, caused a marked accumulation of phaseollin in the cultures. The elicitor induced phaseollin accumulation to a level of 60% that obtained with the artificial elicitor autoclaved ribonuclease A and was maximally active at a concentration (weight basis) of at least 50 times lower than required for maximal response to ribonuclease. (3) Elicitor preparations from cell walls of Phytophthora megasperma var. sojae, a fungal pathogen of soybean, and Botrytis cinerea, the common grey mould, were much less effective than the C. lindemuthianum wall-released elicitor. (4) There was a marked but transient increase in the extractable activity of phenylalanine ammonia-lyase, the enzyme catalysing the first reaction in the biosynthesis of phaseollin from L-phenylalanine, in response to the elicitor from C. lindemuthianum. (5) Comparative density labelling with 2H from 2H2O indicated that the elicitor stimulates de novo synthesis of phenylalanine ammonie findings provide the basis of a scheme for elicitor induction of phytoalexin accumulation.     

Spatial patterns of diversity at the putative recognition domain of resistance gene candidates in wild bean populations

Leucine Rich Repeats (LRR) domains have been identified on most known plant resistance genes and appear to be involved in the specific recognition of pathogen strains. Here we explore the processes which may drive the evolution of this putative recognition domain. We developed AFLP markers specifically situated in the LRR domain of members of the PRLJ1 complex Resistance Gene Candidate (RGC) family identified in common bean (Phaseolus vulgaris). Diversity for these markers was assessed in ten wild populations of P. vulgaris and compared to locally co-occurring pathogen populations of Colletotrichum lindemuthianum. Nine PRLJ1 LRR specific markers were obtained. Marker sequences revealed that RGC diversity at PRLJ1 is similar to that at other complex R-loci. Wild bean populations showed contrasting levels of PRLJ1 LRR diversity and were all significantly differentiated. We could not detect an effect of local C. lindemuthianum population diversity on the spatial distribution of P. vulgaris PRLJ1 diversity. However, host populations have been previously assessed for neutral (RAPD) markers and for resistance phenotypes to six strains of C. lindemuthianum isolated from cultivated bean fields. A comparative analysis of PRLJ1 LRR diversity and host diversity for resistance phenotypes indicated that evolutionary processes related to the antagonistic C. lindemuthianum/P. vulgaris interaction are likely to have shaped molecular diversity of the putative recognition domains of the PRLJ1 RGC family members.     

CLNR1, the AREA/NIT2-like global nitrogen regulator of the plant fungal pathogen Colletotrichum lindemuthianum is required for the infection cycle

Nitrogen starvation is generally assumed to be encountered by biotrophic and hemibiotrophic plant fungal pathogens at the beginning of their infection cycle. We tested whether nitrogen starvation constitutes a cue regulating genes that are required for pathogenicity of Colletotrichum lindemuthianum, a fungal pathogen of common bean. The clnr1 (C. lindemuthianumnitrogen regulator 1) gene, the areA/nit-2 orthologue of C. lindemuthianum, was isolated. The predicted CLNR1 protein exhibits high amino acid sequence similarities with the AREA and NIT2 global fungal nitrogen regulators. Targeted clnr1- mutants are unable to use a wide array of nitrogen sources, indicating that clnr1 is the C. lindemuthianum major nitrogen regulatory gene. The clnr1- mutants are non-pathogenic, although few anthracnose lesions seldom occur on whole plantlets. Surprisingly, cytological analysis reveals that the clnr1- mutants are not disturbed from the penetration stage until the end of the biotrophic phase, but that they are impaired during the setting up of the necrotrophic phase. Thus, through CLNR1, nitrogen starvation constitutes a cue for the regulation of genes that are compulsory for this stage of the C. lindemuthianum infection process. Additionally, clnr1- mutants complemented with the Aspergillus nidulans areA gene are fully pathogenic, indicating that areA is able to activate the C. lindemuthianum suited genes, normally under the control of clnr1.     

通过PCR进行长片段DNA的合成

利用PCR合成DNA长片段(Synthesis Large Frament DNA using PCR,SLFD PCR)是一种有效的合成长片段DNA的方法。采用一段已知的500～600bp碱基的DNA片段为PCR模板,根据所要合成的DNA序列可以设计一系列的PCR引物,这些引物都位于模板DNA的5’端,长度为50～60bp,且从5’到3’方向顺序重叠,重叠碱基数目为12～15,全部引物叠加所得到的DNA正是自己所要合成的DNA。这组引物中最3’端的一条含有一个BamH Ⅰ酶切位点,在该位点后面有15碱基与模板DNA5’端一致的序列。另外还设计一条与该模板匹配的下游引物,引物内也含有一个BamH Ⅰ酶切位点。首先采用5’端最右侧的引物与下游引物进行PCR,在PCR进行10个循环后,以此次PCR的产物为下一轮PCR的模板,该轮PCR采用右侧倒数第二个引物为上游引物,下游引物保持不变。采用类似的方法,完成所有的PCR循环,就可以得到所需要合成的DNA长片段。该方法尤其适合100～200碱基左右的长片段DNA的快速合成与克隆。     

Inheritance of Anthracnose Resistance in the Common Bean Differential Cultivar G 2333 and Identification of a New Molecular Marker Linked to the Co-42 gene

The inheritance of anthracnose resistance of the common bean ( Phaseolus vulgaris L.) differential cultivar G 2333 to Colletotrichum lindemuthianum races 73 and 89 was studied in crosses with the susceptible cultivar Rudá. The segregation ratios of 15 : 1 in the F₂ and 3 : 1 in the backcrosses to Rudá indicate that for each of the races tested there are two independent resistance loci in G 2333. A random amplified polymorphic DNA (RAPD) molecular marker (OPH18_1200C) linked in resistance to race 73 was identified in a BC₃F_2:3 population derived from crosses between Rudá and G 2333. A RAPD molecular marker OPAS13_950C, previously identified as linked to gene Co-4² , was also amplified in this population. Co-segregation analyses showed that these two markers are located at 5.6 (OPH18_1200C) and 11.2 (OPAS13_950C) cM of the Co-4² gene. These markers were not present in BC₁F_2:3 plants resistant to race 89 indicating that this population carries a different resistance gene. DNA amplification of BC₁F_2:3 plants with RAPD molecular marker OPAB_450C, previously identified as linked to gene Co-5 , indicated that this gene is present in this population.     

Induction of glutathione S-transferase genes of Nicotiana benthamiana following infection by Colletotrichum destructivum and C. orbiculare and involvement of one in resistance

Four glutathione S-transferase (GST) genes, NbGSTU1, NbGSTU2, NbGSTU3, and NbGSTF1, were amplified from cDNA of Nicotiana benthamiana leaves infected with Colletotrichum destructivum using primers based on conserved regions of N. tabacum GST sequences. Expression of NbGSTU1 and NbGSTU3 increased progressively during infection by either C. destructivum or Colletotrichum orbiculare, except for a slight decrease by NbGSTU1 late in the infection, whereas NbGSTU2 and NbGSTF1 expression remained relatively constant. Each of the four genes was cloned into a PVX vector for virus-induced gene silencing, and reduced expression of the four genes was detected by RT-PCR. A statistically significant increase in susceptibility of N. benthamiana to infection following gene silencing was found only for NbGSTU1-silenced plants, which had 130% more lesions and 67% more colonization by C. orbiculare compared with control plants. These results demonstrate that the different GST genes respond in different ways to fungal infection, and at least one plant GST gene has an important role in disease development.     

Heteroduplex Mobility Assay for Identification and Phylogenetic Analysis of Anthracnose Fungi

Colletotrichum spp . are casual agents of anthracnose on various economically important crops. To cope with the pitfalls of identifying the fungi by morphotaxonomic criteria, the application of heteroduplex mobility assay (HMA) of internal transcribed spacer (ITS) regions as a biochemical tool was explored. The ITS regions of 29 Colletotrichum isolates including Colletotrichum gloeosporioides , Colletotrichum acutatum , Colletotrichum musae , Colletotrichum graminicola , Colletotrichum capsici , Colletotrichum dematium , Colletotrichum lindemuthianum and three unidentified species of Colletotrichum , were PCR amplified. Comparison of the ITS sequences from 15 Colletotrichum isolates revealed a greater DNA divergence within ITS1 region than that within ITS2. The DNA distance and sequence identity within intra-species ranged from 0.0 to 1.1% and from 98.9 to 100%, respectively; whereas those within inter-species ranged from 1.46 to 13.43% and 90.02 to 98.56%, respectively. From the correlation of DNA distance and relative heteroduplex mobility observed among 15 reference isolates, a formula for estimation of distances of a tested DNA sequence was developed for estimation of DNA distances of a compared strain. The phylogenetic analysis of ITS regions of 29 Colletotrichum isolates using DNA distance inferred from relative heteroduplex mobility divided them into 5 distinctive species groups, namely CG, CA, CC, CM and CL, similar to that assembled based on DNA sequences analysis. Our results show that HMA of ITS regions is a relatively rapid and convenient method for species-specific identification of Colletotrichum spp. The potential use of the established techniques for identification of anthracnose and even other fungal diseases are discussed.     

普通菜豆抗炭疽病基因鉴定与分子标记

菜豆炭疽病是世界菜豆生产中的主要病害之一,使幕豆产量和品质受到严重影响,对抗炭疽病基因的研究可以为培育抗炭疽病品种奠定基础。幕豆炭疽病病菌生理分化比较复杂,由于菜豆品种的抗病性和地域不同,菜豆炭疽菌的致病性分化不同。10个已知抗炭疽病基因中,9个基因（Co-1、Co-2、Co-3／Co-9、Co-4^2、Co-5、Co-6、Co-7、Co-10）已被确认为独立显性基因,其中Co-3／Co-9是等位基因;Co-1、Co-4和Co-9存在等位基因,co-8为隐性基因。除Co-5、Co-7和co-8三个基因还没有被定位外,其他基因被定位在不同的连锁群上。     

Heterokaryon incompatibility is suppressed following conidial anastomosis tube fusion in a fungal plant pathogen

It has been hypothesized that horizontal gene/chromosome transfer and parasexual recombination following hyphal fusion between different strains may contribute to the emergence of wide genetic variability in plant pathogenic and other fungi. However, the significance of vegetative (heterokaryon) incompatibility responses, which commonly result in cell death, in preventing these processes is not known. In this study, we have assessed this issue following different types of hyphal fusion during colony initiation and in the mature colony. We used vegetatively compatible and incompatible strains of the common bean pathogen Colletotrichum lindemuthianum in which nuclei were labelled with either a green or red fluorescent protein in order to microscopically monitor the fates of nuclei and heterokaryotic cells following hyphal fusion. As opposed to fusion of hyphae in mature colonies that resulted in cell death within 3 h, fusions by conidial anastomosis tubes (CAT) between two incompatible strains during colony initiation did not induce the vegetative incompatibility response. Instead, fused conidia and germlings survived and formed heterokaryotic colonies that in turn produced uninucleate conidia that germinated to form colonies with phenotypic features different to those of either parental strain. Our results demonstrate that the vegetative incompatibility response is suppressed during colony initiation in C. lindemuthianum. Thus, CAT fusion may allow asexual fungi to increase their genetic diversity, and to acquire new pathogenic traits.     

Host-Pathogen Interactions: VII. Plant Pathogens Secrete Proteins which Inhibit Enzymes of the Host Capable of Attacking the Pathogen

The results presented demonstrate that microbial pathogens of plants have the ability to secrete proteins which effectively inhibit an enzyme synthesized by the host; an enzyme whose substrate is a constituent of the cell wall of the pathogen. The system in which this was discovered is the anthracnose-causing fungal pathogen (Colletotrichum lindemuthianum) and its host, the French bean (Phaseolus vulgaris). An endo-β-1, 3-glucanase present in the bean leaves is specifically inhibited by a protein secreted by C. lindemuthianum. The cell walls of C. lindemuthianum are shown to be composed largely of a 1, 3-glucan.     

Hybrid characteristics of oligonucleotides consisting of isonucleoside 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol with different linkage modes

Oligonucleotides consisting of the isonucleoside repeating unit 2',5'-anhydro-3'-deoxy-3'-(thymin-1-yl)-D-mannitol (4) were synthesized with the monomeric unit 4 incorporated into oligonucleotides as 1'-->4' linkage 4a (oligomer I) or 6'-->4' linkage 4b (oligomer II). The hybrid properties of the two oligonucleotides I and II with their complementary strands were investigated by thermal denaturation and CD spectra. Oligonucleotide I (4a) formed a stable duplex with d(A)(14) with a slightly reduced T(m) value of 36.6 degrees C, relative to 38.2 degrees C for the control duplex d(T)(14)/d(A)(14), but oligomer II (4b) failed to hybridize with a DNA complementary single strand. The spectrum of the duplex oligomer I/d(A)(14) showed a positive CD band at 217 nm and a negative CD band at 248 nm attributable to a B-like conformation. Molecular modeling showed that in the case of oligomer I: the C6' hydroxy group of each unit could be located in the groove area when hybridized to the DNA single strand, which might contribute additional hydrogen bonding to the stability of duplex formation.     

Rapid Detection of Phytophthora nicotianae in Infected Tobacco Tissues and Soil Samples Based on Its Ypt1 Gene

This paper describes the development of a polymerase chain reaction (PCR) assay for the detection of Phytophthora nicotianae , the causal agent of Phytophthora blight of tobacco and other plants. The PCR primers were designed based on a Ras-related protein ( Ypt 1) gene, and 115 isolates representing 26 species of Phytophthora and 29 fungal species of plant pathogens were used to test the specificity of the primers. PCR amplification with species-specific (Pn) primers resulted in a product of 389 bp only from isolates of P. nicotianae . The detection sensitivity with Pn primers was 1 ng of genomic DNA. Using Ypt 1F/ Ypt 1R as first-round amplification primers, followed by a second round using the primer pair Pn1/Pn2, a nested PCR procedure was developed, which increased the detection sensitivity 100-fold to 10 pg. PCR with the Pn primers could also be used to detect P. nicotianae from naturally infected tobacco tissues and soil. The PCR-based methods developed here could simplify both plant disease diagnosis and pathogen monitoring as well as guide plant disease management.     

Association of Dominant and Recessive Genes Confers Anthracnose Resistance in Stem and Leaves of Common Bean

Different genes might be involved in Colletotrichum lindemuthianum resistance in leaves and stem of common bean. This work aimed to study the genetic mechanisms of the resistance in the leaf and stem in segregating populations from backcrosses involving resistant cultivar AN 910408 and susceptible cultivar Rudá inoculated with spore suspensions of C. lindemuthianum race 83. Our results indicate that two genes which interact epistatically, one dominant and one recessive, are involved in the genetic control of leaf anthracnose resistance. As for stem anthracnose resistance, two genes also epistatic, one dominant and one recessive, explain the resistance to C. lindemuthianum race 83. The recessive gene is the same for leaf and stem resistance; however, the dominant genes are distinct and independent from each other. The three independent resistance genes of AN 910408 observed in this work could be derived from Guanajuato 31.     

Vegetative compatibility and genetic analysis of Colletotrichum lindemuthianum isolates from Brazil

The causal agent of common bean anthracnose, Colletotrichum lindemuthianum, has considerable genetic and pathogenic variability, which makes the development of resistant cultivars difficult. We examined variability within and between Brazilian pathotypes of C. lindemuthianum through the identification of vegetative compatibility groups (VCGs) and by RAPD analysis. Two hundred and ninety-five nit mutants were obtained from 47 isolates of various pathotypes of the fungus collected from different regions, host cultivars and years. In complementation tests, 45 VCGs were identified. Eighteen RAPD primers were employed in the molecular analyses, producing 111 polymorphic bands. Estimates of genetic similarities, determined from the Sorence-Dice coefficient, ranged from 0.42 to 0.97; the dendrogram obtained by cluster analysis revealed 18 groups of isolates. RAPD and VCG markers presented high genotypic diversity. The number of significant associations (P=0.05) between RAPD, VCG and pathogenicity markers ranged from 0 (VCG) to 80% (pathogenicity). The test of multilocus association (rd) for RAPD markers was significantly different from zero (P<0.001), suggesting linkage disequilibrium. However, the results for VCG markers show the presence of recombination mechanisms. In conclusion, RAPD markers and VCGs were useful for detecting genetic variability among isolates of C. lindemuthianum. We found considerable diversity among isolates from the same geographic origin within a short interval; this suggests rapid evolution. There is a need for further studies to elucidate the population structure of this pathogen in agro-ecosystems.