| Summary: | R2R3-MYB protein is the most abundant class of MYB transcription factor family in plants. The transcript profiles of two E4 races of <i>Melampsora larici-populina</i>-tolerant poplars and an intolerant poplar were investigated to characterise the role of the R2R3-MYB family genes in the poplar–E4 interaction. In this study, 217 R2R3-MYBs were identified, and 83 <i>R2R3-MYB</i> genes were assigned to 22 different coexpression modules by weighted gene coexpression network analysis. Most <i>R2R3-MYB</i> genes were unchanged in the early period of E4 infection in both tolerant and intolerant poplars. However, there were obvious increases in differentially expressed <i>R2R3-MYB</i> genes in tolerant poplars at 2 and 4 dpi when defence responses occurred, suggesting that differently expressed <i>R2R3-MYB</i> genes at these time points may play an important role in poplar resistance to E4 infection. In total, 34 <i>R2R3-MYB</i> genes showed differential expression at 2 and 4 dpi between tolerant and intolerant poplars. Among them, 16 differentially expressed <i>R2R3-MYB</i> genes were related to 43 defence-related genes that had significant differences between tolerant and intolerant poplars. There might be coregulatory relationships between R2R3-MYBs and other TFs during poplar–E4 interaction. Some differentially expressed <i>R2R3-MYB</i> genes were related to genes involved in flavonoid biosynthesis and IAA or free SA signal transduction and might help activate defence response during poplar–E4 interaction. MYB194 could be an important node in the convergence of IAA and SA signalling.
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