Unrelated fungal rust candidate effectors act on overlapping plant functions

Rust fungi are plant pathogens that cause epidemics which threatens the production of many important plant species, such as wheat, soy, coffee and poplar. Melampsora larici-populina (Mlp) causes the poplar rust and encodes at least 1 184 candidate effectors (CEs), however their functions are poorly known. In this study, we analysed the transcriptome and metabolome of Arabidopsis constitutively expressing CEs of Mlp to discover processes targeted by these fungal proteins. For this purpose, we sequenced the transcriptome and used mass spectrometry to analyse the metabolome of Arabidopsis plants expressing one of 14 selected CEs and of a control line. We found 2 299 deregulated genes in at least one of the 14 transgenic lines. Among the down-regulated genes, the KEGG pathways MAPK signaling pathway and Plant-pathogen interaction were over-represented in six and five of the 14 transgenic lines, respectively. Moreover, the genes down-regulated across the fourteen transgenic lines are related to hormone response and defense. Regarding the metabolome, there were 680 metabolites deregulated across the 14 transgenic lines, with highly unsaturated and phenolic compounds and peptides enriched among down-regulated and up-regulated metabolites, respectively, in almost all transgenic lines. Interestingly, we found that some transgenic lines expressing CEs with no similarity in amino acid sequence had similar patterns of gene and metabolite deregulation, while plants expressing CEs from the same family deregulated different genes and metabolites. Taken together, our results indicate that the sequence of effectors may not be a good predictor of its impact in the plant.