Differential alteration of plant functions by homologous fungal candidate effectors

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. Overall design: RNA was extracted from pooled aerial tissue of 2-week-old soil-grown plants, using three replicates per genotype, with the Plant Total RNA Mini Kit (Geneaid) using RB buffer following manufacturer's protocol. The samples were treated with DNAse, then RNA quality was assessed using agarose gel electrophoresis. QC was performed using a 2100 Bioanalyzer (Agilent) and only samples having an RNA Integrity Number higher than 7 were kept for library preparation. Libraries were generated with the NeoPrep Library Prep System (Illumina) using the TruSeq Stranded mRNA Library Prep kit (Illumina) and 100 ng of total RNA as per the manufacturer's recommendations. The libraries were then sequenced with Illumina HiSeq 4000 Sequencer with paired-end reads of 100 nt at the Genome Quebec Innovation Centre (McGill University, Montreal, Canada).