Identification and monitoring of Ulmus americana transcripts during in vitro interactions with the Dutch elm disease pathogen Ophiostoma novo-ulmi

Abstract

Molecular mechanisms underlying the interaction leading to Dutch elm disease were studied in vitro using Ulmus americana L. callus culture inoculated with budding cells of the fungal pathogen Ophiostoma novo-ulmi (Brasier). An interaction cDNA library employing suppression subtractive hybridization was constructed from infected elm callus tissue 72 h post-inoculation. Five hundred and thirty-five expressed sequence tags, mostly from the host, were grouped into 314 unisequences and distributed into functional categories. After differential screening, 53 U. americana unisequences were considered upregulated during the interaction. The expression profiles at six time points of a subset of 18 elm transcripts were analyzed in more detail by quantitative reverse-transcriptase polymerase chain reaction. Upregulated sequences included transcripts with sequence similarity to genes coding for different classes of pathogenesis-related proteins and enzymes belonging to different branches of the phenylpropanoid pathway. The possible association with compartmentalization-related compounds and phytoalexin production is discussed. This study provides, for the first time, snapshots of molecular mechanisms involved in the compatible interaction between U. americana and O. novo-ulmi. The interaction library dataset also represents a valuable genomic resource for the highly appreciated urban tree U. americana.