DeepSuperSage analysis of the Vicia faba transcriptome in response to Ascochyta fabae infection

Abstract

Understanding the host response to Ascochyta fabae in faba bean (Vicia faba L.), is crucial to elucidate the biology of host resistance. In an attempt to unravel the faba bean – A. fabae interaction, we performed genome-wide transcriptome profiling by deepSuperSAGE that quantified the early transcriptional changes elicited by the fungus in the resistant 29H faba bean genotype. The total number of 26 bp tags obtained was 1,313,009, of which 51,484 were unique sequences (UniTags) and 161 of them corresponded to fungal sequences. Sequences with a full match of the 26 bp revealed 2,222 tags with a significant P-value that were expressed differentialy between inoculated and control leaves. After gene ontology (GO) annotation, 2,143 of these matched to databases sequences (approximately 1/3 into each GO domain). At a 2.7-fold change threshold, 1,197 sequences were significantly differentially expressed in infected as compared to control leaves. Of these, nearly half were up- and the other downregulated. The most enriched GO terms corresponded to tags related with photosynthesis metabolism or structural components. Ten of them can be associated with plant defense, due to their association with responses to the jasmonic acid pathway, pectin esterase activity or gene silencing. Validation of the SuperSAGE data by qPCR of ten differentially expressed UniTags confirmed a rapid increase or decrease in mRNA 8 to 12 hours after inoculation in most of the up-regulated tags and, less consistently, in the downregulated ones. This study represents the most comprehensive analysis of the Ascochyta-response transcriptome of faba bean available to date. The applicability of these tags will increase as more faba bean genomic and cDNA sequences become available.