Differential gene expression in Alternaria gaisen exposed to dark and light

Abstract

Character states during sporulation have been used to segregate and describe many small-spored species of Alternaria, but some are not supported by published phylogenetic analyses. The conidiation response of Alternaria gaisen was characterized by selective subtractive hybridization of cDNA produced from cultures of A. gaisen grown either in total darkness or in total darkness followed by scarification and 24 h exposure to light. Transcripts or their translation products were identified using BLAST. Multiple transcripts with similarity to ORF-1 of the AM-toxin gene were obtained from the light library. L152 is a full reading frame EST in the light library whose ORF translation has similarity to the conserved domain aegerolysin (pfam06355). A set of 11 ex-type or representative isolates including A. alternata, A. gaisen, A. yaliinficiens, A. arborescens, A. tenuissima and A. brassicicola were resolved by UPGMA analysis of a partial genomic sequence (415–425 base pairs) of L152, but were not resolved by a similar analysis of ITS sequences. Furthermore, the resolved lineages of the L152 dataset were reflective of the diversity previously hypothesized by morphological evaluations of sporulation patterns. Although the ITS rDNA sequence region is generally accepted as the most likely candidate for fungal barcoding, the analysis of L152 sequences presented here resolved closely related species or species groups where other loci, including ITS, have not. Based on these results, the sequences of putative aegerolysin homologs were variable, parsimony-informative and warrant additional analyses with a broader isolate set including related genera and species.