Identification of plant genes involved on the initial contact between ectomycorrhizal symbionts (Castanea sativa – European chestnut and Pisolithus tinctorius)

In order to contribute to the knowledge on the genes involved in the early steps of ectomycorrhiza development, the transcriptional response of Castanea sativa (European chestnut) during the initial contact (6 and 12 h) with Pisolithus tinctorius was analysed by microarray. This study revealed that among the regulated plant genes, a substantial number of up-regulated transcripts showed homology with genes encoding for proteins involved in stress and defense responses, (a cystatin, a cystatin-like protein, a defensin and a universal stress protein). Early contact with the fungal mycelium also altered expression of genes that are putatively involved in cellular processes like signal transduction and communication (receptor kinase-related protein), protein fate (papain-like cystein proteinase), and water transport facilitation (water channel MipK protein). Expression profiling of the early contact between C. sativa and P. tinctorius revealed that changes in gene expression occur few hours after contact, long before the development of a functional mycorrhiza. The induction of genes involved in stress and defense suggests that the host plant reacts rapidly to the presence of the mycobiont eliciting a defense programme similar to that described for pathogenic interactions. Another plant response was the repression of genes normally implicated in water stress accounting for a water stress relief due to the initial contact with the ectomycorrhizal fungus.