Spontaneous loss of a conditionally dispensable chromosome from the Alternaria alternata apple pathotype leads to loss of toxin production and pathogenicity

2001 ◽  
Vol 40 (1) ◽  
pp. 65-72 ◽  
Author(s):  
Linda J. Johnson ◽  
Richard D. Johnson ◽  
Hajime Akamatsu ◽  
Achmadi Salamiah ◽  
Hiroshi Otani ◽  
...  
Keyword(s):  
Alternaria Alternata ◽  
Toxin Production ◽  
Dispensable Chromosome

scholarly journals Functional Analysis of a Multicopy Host-Selective ACT-Toxin Biosynthesis Gene in the Tangerine Pathotype of Alternaria alternata Using RNA Silencing

2008 ◽  
Vol 21 (12) ◽  
pp. 1591-1599 ◽  
Author(s):  
Y. Miyamoto ◽  
A. Masunaka ◽  
T. Tsuge ◽  
M. Yamamoto ◽  
K. Ohtani ◽  
...  
Keyword(s):  
Alternaria Alternata ◽  
Rna Silencing ◽  
Toxin Production ◽  
Brown Spot ◽  
Plasmid Construct ◽  
Dispensable Chromosome ◽  
Alternaria Brown Spot ◽  
Multiple Copies ◽  
Commercially Important ◽  
Serious Disease

Alternaria brown spot, caused by the tangerine pathotype of Alternaria alternata, is a serious disease of commercially important tangerines and their hybrids. The pathogen produces host-selective ACT toxin, and several genes (named ACTT) responsible for ACT-toxin biosynthesis have been identified. These genes have many paralogs, which are clustered on a small, conditionally dispensable chromosome, making it difficult to disrupt entire functional copies of ACTT genes using homologous recombination-mediated gene disruption. To overcome this problem, we attempted to use RNA silencing, which has never been employed in Alternaria spp., to knock down the functional copies of one ACTT gene with a single silencing event. ACTT2, which encodes a putative hydrolase and is present in multiple copies in the genome, was silenced by transforming the fungus with a plasmid construct expressing hairpin ACTT2 RNAs. The ACTT2 RNA-silenced transformant (S-7-24-2) completely lost ACTT2 transcripts and ACT-toxin production as well as pathogenicity. These results indicated that RNA silencing may be a useful technique for studying the role of ACTT genes responsible for host-selective toxin biosynthesis in A. alternata. Further, this technique may be broadly applicable to the analysis of many genes present in multiple copies in fungal genomes that are difficult to analyze using recombination-mediated knockdowns.

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 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.

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.

scholarly journals Metabolic regulation of host-specific toxin production in Alternaria alternata pathogens. 2. Suppression of toxin production from germinating spores by chemical treatments.

1985 ◽  
Vol 51 (3) ◽  
pp. 277-284
Author(s):  
Takashi TSUGE ◽  
Syoyo NISHIMURA ◽  
Satoshi OMURA ◽  
Keisuke KOHMOTO ◽  
Hiroshi OTANI
Keyword(s):  
Alternaria Alternata ◽  
Metabolic Regulation ◽  
Toxin Production ◽  
Chemical Treatments

scholarly journals Genomic features and evolution of the conditionally dispensable chromosome in the tangerine pathotype of Alternaria alternata

2017 ◽  
Author(s):  
Mingshuang Wang ◽  
Huilan Fu ◽  
Xing-Xing Shen ◽  
Ruoxin Ruan ◽  
Nicholas Pun ◽  
...  
Keyword(s):  
Gene Transfer ◽  
Horizontal Gene Transfer ◽  
Gene Cluster ◽  
Alternaria Alternata ◽  
Deletion Mutant ◽  
Metabolic Process ◽  
Brown Spot ◽  
P Value ◽  
Dispensable Chromosome ◽  
Cdc Genes

AbstractThe tangerine pathotype of the ascomycete fungus Alternaria alternata is the causal agent of citrus brown spot, which can result in significant losses of both yield and marketability for tangerines and tangerine hybrids worldwide. A conditionally dispensable chromosome (CDC), which harbors the host-selective ACT toxin gene cluster, is required for tangerine pathogenicity of A. alternata. To understand the genetic makeup and evolution of the tangerine pathotype CDC, we analyzed the function and evolution of the CDC genes present in the A. alternata Z7 strain. The 1.84Mb long CDC contains 512 predicted protein-coding genes, which are enriched in functional categories associated with ‘metabolic process’ (132 genes, p-value = 0.00192) including ‘oxidation-reduction process’ (48 genes, p-value = 0.00021) and ‘lipid metabolic process’ (11 genes, p-value = 0.04591). Relatively few of the CDC genes can be classified as CAZymes (13), kinases (3) and transporters (20). Differential transcriptome analysis of H2O2 treatment and control conditions revealed that 29 CDC genes were significantly up-regulated and 14 were significantly down-regulated, suggesting that CDC genes may play a role in coping with oxidative stress. Evolutionary analysis of the 512 CDC proteins showed that their evolutionary conservation tends to be restricted within the genus Alternaria and that the CDC genes evolve faster than genes in the essential chromosomes. Interestingly, phylogenetic analysis suggested that the genes of 13 enzymes and one sugar transporter residing in the CDC were likely horizontally transferred from distantly related species. Among these, one carboxylesterase gene was transferred from bacteria but functionally knocking out this gene revealed no obvious biological role. Another 4 genes might have been transferred from Colletotrichum (Sordariomycetes) and 5 were likely transferred as a physically linked cluster of genes from Cryptococcus (Basidiomycota) or Penicillium (Eurotiomycetes). Functionally knocking out the 5-gene cluster resulted in an 80% decrease in asexual spore production in the deletion mutant. These results provide new insights into the function and evolution of CDC genes in Alternaria.Author SummaryMany fungal phytopathogens harbor conditionally dispensable chromosomes (CDCs). CDCs are variable in size, contain many genes involved in virulence, but their evolution remains obscure. In this study, we investigated the origin of the CDC present in the tangerine pathotype of Alternaria alternata Z7 strain. We found that most of the Z7 CDC proteins are highly conserved within the genus Alternaria but poorly conserved outside the genus. We also discovered that a small number of genes originated via horizontal gene transfer (HGT) from distantly related fungi and bacteria. These horizontally transferred genes include a carboxylesterase gene that was likely acquired from bacteria, a cluster of 4 physically linked genes likely transferred from Colletotrichum, and a cluster of 5 physically linked genes likely transferred from Cryptococcus (Basidiomycota) or Penicillium (Eurotiomycetes). To gain insight into the functions of these transferred genes, we knocked out the bacterial carboxylesterase and the 5-gene cluster. Whereas the carboxylesterase deletion mutant showed no obvious phenotype, the 5-gene cluster mutant showed a dramatically reduced production of asexual spores (conidia). The results of our study suggest that Alternaria CDCs are largely comprised from rapidly evolving native genes; although only a few genes were acquired via horizontal gene transfer, some of them appear to be involved in functions critical to the phytopathogenic lifestyle.

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