The two sides of the same coin: RNAseq analysis of rough lemon leaves (Citrus jambhiri Lush.) infected by P. tracheiphilus reveals plant genes of survival and fungal strategies to defeat host

The etiologic agent of the mal secco disease is the fungus Plenodomus tracheiphilus, which mainly affects the survival of lemons in the Mediterranean area. Currently, we can estimate that the disease pressure has led to a reduction of more than 80% of the lemon-planted area in the last 30 years, with high economic losses in terms of job and industrial production. Building upon an RNA-seq analysis, we performed a KEGG enrichment analysis of either host or pathogen transcripts leading to the identification of upregulated genes that might have a crucial role during host-pathogen interaction. In particular, within the “nitrogen metabolism” and “carbon metabolism” categories, genes involved in 2-oxoglutarate production, either in plants or in fungi, were found highly expressed. In planta, this event is probably functional to cope with the disease ongoing by feeding the tri-carboxyl acid cycle. Otherwise, it might ensure the needed levels of 2-oxoglutarate to supply fungus of energetic metabolites (via the TCA cycle), toxins, and melatin as observed in other species.