scholarly journals Metabolic regulation of host-specific toxin production in Alternaria alternata pathogens. 3. Instability of pathogenicity in field isolates of A. alternata Japanese pear pathotype.

1986 ◽  
Vol 52 (3) ◽  
pp. 488-491 ◽  
Author(s):  
Takashi TSUGE ◽  
Noriki HAYASHI ◽  
Syoyo NISHIMURA
Keyword(s):  
Alternaria Alternata ◽  
Metabolic Regulation ◽  
Toxin Production ◽  
Japanese Pear ◽  
Field Isolates

scholarly journals Distribution and Characterization of AKT Homologs in the Tangerine Pathotype of Alternaria alternata

2000 ◽  
Vol 90 (7) ◽  
pp. 762-768 ◽  
Author(s):  
A. Masunaka ◽  
A. Tanaka ◽  
T. Tsuge ◽  
T. L. Peever ◽  
L. W. Timmer ◽  
...  
Keyword(s):  
Alternaria Alternata ◽  
Sequence Similarity ◽  
Structural Similarity ◽  
Toxin Production ◽  
Brown Spot ◽  
Japanese Pear ◽  
Black Rot ◽  
Acid Moiety ◽  
High Sequence Similarity ◽  
Rough Lemon

The tangerine pathotype of Alternaria alternata produces a host-selective toxin (HST), known as ACT-toxin, and causes Alternaria brown spot disease of citrus. The structure of ACT-toxin is closely related to AK- and AF-toxins, which are HSTs produced by the Japanese pear and strawberry pathotypes of A. alternata, respectively. AC-, AK-, and AF-toxins are chemically similar and share a 9,10-epoxy-8-hydroxy-9-methyl-decatrienoic acid moiety. Two genes controlling AK-toxin biosynthesis (AKT1 and AKT2) were recently cloned from the Japanese pear pathotype of A. alternata. Portions of these genes were used as heterologous probes in Southern blots, that detected homologs in 13 isolates of A. alternata tangerine pathotype from Minneola tangelo in Florida. Partial sequencing of the homologs in one of these isolates demonstrated high sequence similarity to AKT1 (89.8%) and to AKT2 (90.7%). AKT homologs were not detected in nine isolates of A. alternata from rough lemon, six isolates of nonpathogenic A. alternata, and one isolate of A. citri that causes citrus black rot. The presence of homologs in the Minneola isolates and not in the rough lemon isolates, nonpathogens or black rot isolates, correlates perfectly to pathogenicity on Iyo tangerine and ACT-toxin production. Functionality of the homologs was demonstrated by detection of transcripts using reverse transcription-polymerase chain reaction (RT-PCR) in total RNA of the tangerine pathotype of A. alternata. The high sequence similarity of AKT and AKT homologs in the tangerine patho-type, combined with the structural similarity of AK-toxin and ACT-toxin, may indicate that these homologs are involved in the biosynthesis of the decatrienoic acid moiety of ACT-toxin.

Circular DNA Plasmid in the Phytopathogenic Fungus Alternaria alternata: Its Temperature-Dependent Curing and Association with Pathogenicity

Genetics ◽  
1997 ◽  
Vol 146 (1) ◽  
pp. 111-120
Author(s):  
Satoshi Katsuya ◽  
Isao Kaneko ◽  
Makiko Owaki ◽  
Kouichi Ishikawa ◽  
Takashi Tsujimoto ◽  
...  
Keyword(s):  
Blot Analysis ◽  
Alternaria Alternata ◽  
Black Spot ◽  
Electron Microscopic Observation ◽  
Toxin Production ◽  
Japanese Pear ◽  
Phytopathogenic Fungus ◽  
Temperature Dependent ◽  
Electron Microscopic ◽  
Endonuclease Mapping

We found the presence of plasmid DNA in strain T88-56 of the Japanese pear pathotype of Alternaria alternata, which causes black spot of certain cultivars of Japanese pear by producing host-specific AK-toxin. The plasmid, designated pAAT56, was identified to be an ∼5.4-kilobase (kb) circular molecule by electron microscopic observation and restriction endonuclease mapping. Southern blot analysis showed that pAAT56 DNA had no homology with either nuclear or mitochondrial DNA. Cultures of strain T88-56 grown at 26° showed markedly reduced plasmid levels relative to those grown at lower temperatures. The strain was completely cured of pAAT56 during growth at 29°. Temperature-dependent curing of pAAT56 was confirmed by using single-protoplast isolates from mycelia grown at 23°, most of which maintained the plasmid, and from mycelia grown at 29°, most of which had lost the plasmid. Northern blot analysis detected the presence of three RNA species (∼1.7, 2.7 and 5.4 kb) transcribed from pAAT56. The biological function of pAAT56 was observed using single-protoplast isolates from mycelia that either contained or had been cured of pAAT56. The plasmid-containing isolates tended to be reduced in AK-toxin production and pathogenicity compared with the plasmid-cured isolates.

scholarly journals Insertional Mutagenesis and Cloning of the Genes Required for Biosynthesis of the Host-Specific AK-Toxin in the Japanese Pear Pathotype of Alternaria alternata

1999 ◽  
Vol 12 (8) ◽  
pp. 691-702 ◽  
Author(s):  
Aiko Tanaka ◽  
Hiroshi Shiotani ◽  
Mikihiro Yamamoto ◽  
Takashi Tsuge
Keyword(s):  
Restriction Enzyme ◽  
Alternaria Alternata ◽  
Type Strain ◽  
Insertional Mutagenesis ◽  
Wild Type Strain ◽  
Black Spot ◽  
Toxin Production ◽  
Japanese Pear ◽  
Wild Type ◽  
Functional Analyses

The Japanese pear pathotype of Alternaria alternata causes black spot of Japanese pear by producing a host-specific toxin known as AK-toxin. Restriction enzyme-mediated integration (REMI) mutagenesis was used to tag genes required for toxin biosynthesis. Protoplasts of a wild-type strain were treated with a linearized plasmid along with the restriction enzyme used to linearize the plasmid. Of 984 REMI transformants recovered, three produced no detectable AK-toxin and lost pathogenicity on pear leaves. Genomic DNA flanking the integrated plasmid was recovered from one of the mutants. With the recovered DNA used as a probe, a cosmid clone of the wild-type strain was isolated. Structural and functional analyses of an 8.0-kb region corresponding to the tagged site indicated the presence of two genes. One, designated AKT1, encodes a member of the class of carboxyl-activating enzymes. The other, AKT2, encodes a protein of unknown function. The essential roles of these two genes in both AK-toxin production and pathogenicity were confirmed by transformation-mediated gene disruption experiments. DNA gel blot analysis detected AKT1 and AKT2 homologues not only in the Japanese pear pathotype strains but also in strains from the tangerine and strawberry pathotypes. The host-specific toxins of these two pathotypes are similar in structure to AK-toxin. Homologues were not detected in other pathotypes or in non-pathogenic strains of A. alternata, suggesting acquisition of AKT1 and AKT2 by horizontal transfer.

scholarly journals Contribution of Peroxisomes to Secondary Metabolism and Pathogenicity in the Fungal Plant Pathogen Alternaria alternata

2010 ◽  
Vol 9 (5) ◽  
pp. 682-694 ◽  
Author(s):  
Ai Imazaki ◽  
Aiko Tanaka ◽  
Yoshiaki Harimoto ◽  
Mikihiro Yamamoto ◽  
Kazuya Akimitsu ◽  
...  
Keyword(s):  
Fatty Acid ◽  
Alternaria Alternata ◽  
Marked Reduction ◽  
Fluorescent Protein ◽  
Toxin Production ◽  
Defense Responses ◽  
Japanese Pear ◽  
Acid Media ◽  
Content Type ◽  
Mutant Strains

ABSTRACT The filamentous fungus Alternaria alternata includes seven pathogenic variants (pathotypes) which produce different host-selective toxins and cause diseases on different plants. The Japanese pear pathotype produces the host-selective AK-toxin, an epoxy-decatrienoic acid ester, and causes black spot of Japanese pear. Previously, we identified four genes, AKT1, AKT2, AKT3, and AKTR, involved in AK toxin biosynthesis. AKT1, AKT2, and AKT3 encode enzyme proteins with peroxisomal targeting signal type 1 (PTS1)-like tripeptides, SKI, SKL, and PKL, respectively, at the C-terminal ends. In this study, we verified the peroxisome localization of Akt1, Akt2, and Akt3 by using strains expressing N-terminal green fluorescent protein (GFP)-tagged versions of the proteins. To assess the role of peroxisome function in AK-toxin production, we isolated AaPEX6, which encodes a peroxin protein essential for peroxisome biogenesis, from the Japanese pear pathotype and made AaPEX6 disruption-containing transformants from a GFP-Akt1-expressing strain. The ΔAaPEX6 mutant strains did not grow on fatty acid media because of a defect in fatty acid β oxidation. The import of GFP-Akt1 into peroxisomes was impaired in the ΔAaPEX6 mutant strains. These strains completely lost AK toxin production and pathogenicity on susceptible pear leaves. These data show that peroxisomes are essential for AK-toxin biosynthesis. The ΔAaPEX6 mutant strains showed a marked reduction in the ability to cause lesions on leaves of a resistant pear cultivar with defense responses compromised by heat shock. This result suggests that peroxisome function is also required for plant invasion and tissue colonization in A. alternata. We also observed that mutation of AaPEX6 caused a marked reduction of conidiation.

scholarly journals Studies on variability in Alternaria alternata (Kessler) causing leaf blight of Isabgol (Plantago ovata)

2015 ◽  
Vol 12 (2) ◽  
pp. 63-70 ◽  
Author(s):  
RK Meena ◽  
SS Sharma ◽  
S Singh
Keyword(s):  
Alternaria Alternata ◽  
Mycelial Growth ◽  
Toxin Production ◽  
Plantago Ovata ◽  
Mycelium Growth ◽  
Highly Pathogenic ◽  
Fast Growing ◽  
Conidial Morphology ◽  
Incubation Periods ◽  
Pathogenic Variability

All the five isolates of Alternaria alternata isolated from different agro climate zone of Rajasthan were tested for their variability in terms of cultural, conidial, pathogenic characteristics and toxin production. All the five isolates differed in cultural characters i.e. dark black colored and very fast mycelial growth with smooth margins (90.00 mm), light black with white at centre and fast growing (80.00 mm), dark brown and medium mycelium growth with smooth margins (75.00 mm), black colored, medium flat mycelial growth with smooth margins (68.00 mm) and white with slightly black in colour with slow mycelial growth (65.00 mm) were observed in Aa-1, Aa-2, Aa-3, Aa-4 and Aa-5 respectively. The variability in conidial morphology of five different isolates was simple, septate, pale to dark brown in colour, often geniculate with one conidial scar. In respect of pathogenic variability, showed significant variations in terms of disease intensity and incubation periods. The isolates Aa-1 was highly pathogenic on Isabgol cv. RI-89 under artificial inoculation conditions showing 52.12% disease intensity followed by Aa- 3 ,Aa-2, Aa-4 and Aa-5 isolates. The variability in toxin production was reflected in terms of time taken in inducing wilting symptoms of Isabgol cuttings. Isolate Aa-1 was highly toxic followed by isolates Aa-2, Aa-3, Aa-4 and Aa-5. DOI: http://dx.doi.org/10.3329/sja.v12i2.21918 SAARC J. Agri., 12(2): 63-70 (2014)

scholarly journals Role of the Host-Selective ACT-Toxin Synthesis Gene ACTTS2 Encoding an Enoyl-Reductase in Pathogenicity of the Tangerine Pathotype of Alternaria alternata

2010 ◽  
Vol 100 (2) ◽  
pp. 120-126 ◽  
Author(s):  
Naoya Ajiro ◽  
Yoko Miyamoto ◽  
Akira Masunaka ◽  
Takashi Tsuge ◽  
Mikihiro Yamamoto ◽  
...  
Keyword(s):  
Alternaria Alternata ◽  
Essential Gene ◽  
Toxin Production ◽  
Brown Spot ◽  
Gene Encoding ◽  
Bac Clone ◽  
Biosynthesis Gene Cluster ◽  
Enoyl Reductase ◽  
Alternaria Brown Spot ◽  
Rapid Amplification

The tangerine pathotype of Alternaria alternata produces host-selective ACT-toxin and causes Alternaria brown spot disease of tangerines and tangerine hybrids. Sequence analysis of a genomic BAC clone identified a previously uncharacterized portion of the ACT-toxin biosynthesis gene cluster (ACTT). A 1,034-bp gene encoding a putative enoyl-reductase was identified by using rapid amplification of cDNA ends and polymerase chain reaction and designated ACTTS2. Genomic Southern blots demonstrated that ACTTS2 is present only in ACT-toxin producers and is carried on a 1.9 Mb conditionally dispensable chromosome by the tangerine pathotype. Targeted gene disruption of ACTTS2 led to a reduction in ACT-toxin production and pathogenicity, and transcriptional knockdown of ACTTS2 using RNA silencing resulted in complete loss of ACT-toxin production and pathogenicity. These results indicate that ACTTS2 is an essential gene for ACT-toxin biosynthesis in the tangerine pathotype of A. alternata and is required for pathogenicity of this fungus.

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