Transcriptomic analysis of the interactions between Agaricus bisporus and Lecanicillium fungicola

• SSH identified A. bisporus genes up- and down-regulated during L. fungicola infection.
• ESTs of L. fungicola identified candidate pathogenicity-related genes.
• Commercial A. bisporus lines show some transcriptional response to infection.
• Silencing of chitin deacetylase or DAHPs in A. bisporus was rather variable but failed to alter susceptibility.

Agaricus bisporus is susceptible to a number of diseases, particularly those caused by fungi, with Lecanicillium fungicola being the most serious. Control of this disease is important for the security of crop production, however given the lack of knowledge about fungal–fungal interactions, such disease control is rather limited. Exploiting the recently released genome sequence of A. bisporus, here we report studies simultaneously investigating both the host and the pathogen, focussing on transcriptional changes associated with the cap spotting lesions typically seen in this interaction. Forward-suppressive subtractive hybridisation (SSH) analysis identified 68 A. bisporus unigenes induced during infection. Chitin deacetylase showed the strongest response, with almost 1000-fold up-regulation during infection, so was targeted for down-regulation by silencing to see if it was involved in defence against L. fungicola. Transgenic lines were made expressing hairpin RNAi constructs, however no changes in susceptibility to L. fungicola were observed. Amongst the other up-regulated genes there were none with readily apparent roles in resisting infection in this susceptible interaction.Reverse-SSH identified 72 unigenes from A. bisporus showing reduced expression, including two tyrosinases, several genes involved in nitrogen metabolism and a hydrophobin. The forward-SSH analysis of infected mushrooms also yielded 64 unigenes which were not of A. bisporus origin and thus derived from L. fungicola. An EST analysis of infection-mimicking conditions generated an additional 623 unigenes from L. fungicola including several oxidoreductases, cell wall degrading enzymes, ABC and MFS transporter proteins and various other genes believed to play roles in other pathosystems.Together, this analysis shows how both the pathogen and the host modify their gene expression during an infection–interaction, shedding some light on the disease process, although we note that some 40% of unigenes from both organisms encode hypothetical proteins with no ascribed function which highlights how much there is still to discover about this interaction.