Submitted to: Mycopathologia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2006
Publication Date: 2/8/2007
Citation: Hua, S.T., Tarun, A.S., Pandey, S.N., Chang, L.Y., Chang, P. 2007. Characterization of AFLAV, a Tfl/Sushi retrotransposon from Aspergillus flavus. Mycopathologia. 163(2):97-104. Interpretive Summary: Aspergillus flavus is an important fungus in food safety. There is very little information on the genetic structure of retrotransposon in this species. This is the first report to provide a detailed description of AFLAV (retrotransposon fo Aspergillus flavus). Up to now, retrotransposon isolated from Aspergillus species, such as Dane1 and Dane2 of A. nidulans and Afut1 and Afut2 of A. fumigatus are all apparently degenerated LTR retrotransposons and may be no longer active. Our studies demonstrate that A. flavus strain NRRL 6541 has complete retrotransposons integrated in the chromosomes. Our survey indicates that fifty percent of the A. flavus strains from different geological regions probably have full length AFLAV in the genomes. The sequence features of intact AFLAV imply that this retroelement may be active and could have contributed to the diversity of A. flavus populations observed in cotton, peanut and corn fields. The results of this study will impact future studies on the influence of this element on gene expression and diversity of A. flavus populations.
Technical Abstract: The insert of pAF28 contains a 4.5 kb region which encodes a truncated retrotransposon (AfRTL-1). In search for a full-length and intact copy of retrotransposon, we exploited a novel PCR cloning strategy by amplifying a 3.4 kb region from the genomic DNA of A. flavus NRRL 6541. The fragment was cloned into pCR®4-TOPO®. Sequence analysis confirmed that this region encoded putative domains of partial reverse transcriptase, RNase H, and integrase of the predicted retrotransposon. The two flanking long terminal repeats (LTRs) and the sequence between them comprise a putative full-length LTR retrotransposon of 7799 bp in length. This intact retrotranspson sequence is named AFLAV (A. flavus Retrotransposon). The order of the predicted catalytic domains in the polyprotein (Pol) placed AFLAV in the Tf1/sushi subgroup of the Ty3/gypsy retrotransposon family. Primers derived from AFLAV sequence were used to screen this retrotransposon in other strains of A. flavus. More than fifty strains of A. flavus isolated from different geological origins were surveyed and the results show that many strains have extensive deletions in the regions encoding the capsid (Gag) and Pol.