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Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus.

ABSTRACT: The tomato pathotype of Alternaria alternata produces host-specific AAL toxin and causes Alternaria stem canker on tomato. A polyketide synthetase (PKS) gene, ALT1, which is involved in AAL toxin biosynthesis, resides on a 1.0-Mb conditionally dispensable chromosome (CDC) found only in the pathogenic and AAL toxin-producing strains. Genomic sequences of ALT1 and another PKS gene, both of which reside on the CDC in the tomato pathotype strains, were compared to those of tomato pathotype strains collected worldwide. This revealed that the sequences of both CDC genes were identical among five A. alternata tomato pathotype strains having different geographical origins. On the other hand, the sequences of other genes located on chromosomes other than the CDC are not identical in each strain, indicating that the origin of the CDC might be different from that of other chromosomes in the tomato pathotype. Telomere fingerprinting and restriction fragment length polymorphism analyses of the A. alternata strains also indicated that the CDCs in the tomato pathotype strains were identical, although the genetic backgrounds of the strains differed. A hybrid strain between two different pathotypes was shown to harbor the CDCs derived from both parental strains with an expanded range of pathogenicity, indicating that CDCs can be transmitted from one strain to another and stably maintained in the new genome. We propose a hypothesis whereby the ability to produce AAL toxin and to infect a plant could potentially be distributed among A. alternata strains by horizontal transfer of an entire pathogenicity chromosome. This could provide a possible mechanism by which new pathogens arise in nature.

SUBMITTER: Akagi Y

PROVIDER: S-EPMC2772402 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus.

Akagi Yasunori Y Akamatsu Hajime H Otani Hiroshi H Kodama Motoichiro M

Eukaryotic cell 20090911 11

The tomato pathotype of Alternaria alternata produces host-specific AAL toxin and causes Alternaria stem canker on tomato. A polyketide synthetase (PKS) gene, ALT1, which is involved in AAL toxin biosynthesis, resides on a 1.0-Mb conditionally dispensable chromosome (CDC) found only in the pathogenic and AAL toxin-producing strains. Genomic sequences of ALT1 and another PKS gene, both of which reside on the CDC in the tomato pathotype strains, were compared to those of tomato pathotype strains c ...[more]

PMID: 19749175

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Project description:BackgroundGenomes of Methanosarcina spp. are among the largest archaeal genomes. One suggested reason for that is massive horizontal gene transfer (HGT) from bacteria. Genes of bacterial origin may be involved in the central metabolism and solute transport, in particular sugar synthesis, sulfur metabolism, phosphate metabolism, DNA repair, transport of small molecules etc. Horizontally transferred (HT) genes are considered to play the key role in the ability of Methanosarcina spp. to inhabit diverse environments. At the moment, genomes of three Methanosarcina spp. have been sequenced, and while these genomes vary in length and number of protein-coding genes, they all have been shown to accumulate HT genes. However, previous estimates had been made when fewer archaeal genomes were known. Moreover, several Methanosarcinaceae genomes from other genera have been sequenced recently. Here, we revise the census of genes of bacterial origin in Methanosarcinaceae.ResultsAbout 5% of Methanosarcina genes have been shown to be horizontally transferred from various bacterial groups to the last common ancestor either of Methanosarcinaceae, or Methanosarcina, or later in the evolution. Simulation of the composition of the NCBI protein non-redundant database for different years demonstrates that the estimates of the HGT rate have decreased drastically since 2002, the year of publication of the first Methanosarcina genome. The phylogenetic distribution of HT gene donors is non-uniform. Most HT genes were transferred from Firmicutes and Proteobacteria, while no HGT events from Actinobacteria to the common ancestor of Methanosarcinaceae were found. About 50% of HT genes are involved in metabolism. Horizontal transfer of transcription factors is not common, while 46% of horizontally transferred genes have demonstrated differential expression in a variety of conditions. HGT of complete operons is relatively infrequent and half of HT genes do not belong to operons.ConclusionsWhile genes of bacterial origin are still more frequent in Methanosarcinaceae than in other Archaea, most HGT events described earlier as Methanosarcina-specific seem to have occurred before the divergence of Methanosarcinaceae. Genes horizontally transferred from bacteria to archaea neither tend to be transferred with their regulators, nor in long operons.

Dataset Information

Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus.

Publications

Horizontal chromosome transfer, a mechanism for the evolution and differentiation of a plant-pathogenic fungus.

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