Transposons in filamentous fungi-facts and perspectives

Abstract

Transposons are ubiquitous genetic elements discovered so far in all investigated prokaryotes and eukaryotes. In remarkable contrast to all other genes, transposable elements are able to move to new locations within their host genomes. Transposition of transposons into coding sequences and their initiation of chromosome rearrangements have tremendous impact on gene expression and genome evolution. While transposons have long been known in bacteria, plants, and animals, only in recent years has there been a significant increase in the number of transposable elements discovered in filamentous fungi. Like those of other eukaryotes, each fungal transposable element is either of class I or of class II. While class I elements transpose by a RNA intermediate and employ reverse transcriptases, class II elements transpose directly at the DNA level. We present structural and functional features for such transposons that have been identified so far in filamentous fungi. Emphasis is given to specific advantages or unique features when fungal systems are used to study transposable elements, e.g., the evolutionary impact of transposons in coenocytic organisms and possible experimental approaches toward horizontal gene transfer. Finally, we focus on the potential of transposons for tagging and identifying fungal genes.

The biology and potential for genetic research of transposable elements in filamentous fungi

“…More detailed descriptions on the biology of transposons in filamentous fungi have been published especially for species of agricultural, biotechnological and medical interest (see reviews by Oliver, 1992;Kistler and Miao, 1992), although the sexual stage has not been described for most of these species which generally show a high level of genetic variability (Daboussi, 1997;Kempken and Kück, 1998). The study of the transposons in these technologically useful species led to the discovery of many types of elements, covering practically the whole spectrum of transposable eukaryotic elements (Daboussi, 1997;Kempken and Kück, 1998).…”

“…In the Metaviridae the pol genes are ordered in the sequence protease/reverse transcriptase/RnaseH/integrase while in the Pseudoviridae the order of the pol genes is protease/integrase/reverse transcriptase/RnaseH (Figure 2). In previous revisions (Daboussi, 1996;Kempken and Kück, 1998;Daboussi and Capy, 2003), the classification of the LTR retroelements was based on their similarity to gypsy elements (equivalent to the Metaviridae) and copia elements (equivalent to the Pseudoviridae).…”

“…Several transposons have been cloned and identified by comparison with elements described in other organisms but this method does not show whether these sequences remain active. This strategy is particularly appropriate to identify high copy number transposons regardless of their activity (Kempken and Kück, 1998). Some examples of elements identified by this strategy are the foret1 and palm transposons of F. oxysporum (Julien et al, 1992;Mouyna et al, 1996) and the cgt1 and cgret elements of C. gloeosporioides (He et al, 1996;Zhu and Oudemans, 2000).…”

“…the ascomycetes Neurospora crassa and Aspergillus nidulans) showed that they contain silenced transposons, the loss of activity of which may be the consequence of continuous selection for phenotypic stability and the action of several mechanisms of genetic silencing which inactivate repeated sequences, including transposable elements (Selker, 1999;Faugeron, 2000;Cogoni, 2001). More detailed descriptions on the biology of transposons in filamentous fungi have been published especially for species of agricultural, biotechnological and medical interest (see reviews by Oliver, 1992;Kistler and Miao, 1992), although the sexual stage has not been described for most of these species which generally show a high level of genetic variability (Daboussi, 1997;Kempken and Kück, 1998). The study of the transposons in these technologically useful species led to the discovery of many types of elements, covering practically the whole spectrum of transposable eukaryotic elements (Daboussi, 1997;Kempken and Kück, 1998).…”

Cercospora kikuchii aislada en la provincia de Santa Fe (Argentina): variabilidad genética y producción de cercosporina in vitro

“…De acuerdo con Kempken y cols. [11], los transposones también pueden incrementar la heterogeneidad en los hongos. El hecho de que la cepa CK6711 (colección japonesa) no se agrupara con ninguno de los demás aislamientos evaluados podría atribuirse a que no está epidemiológicamente relacionada con el resto.…”