Comprehensive Genome-Wide Analyses of Poplar R2R3-MYB Transcription Factors and Tissue-Specific Expression Patterns under Drought Stress.

R2R3-type MYB transcription factors are implicated in drought stress, which is a primary factor limiting the growth and development of woody plants. The identification of genes in the genome has been previously reported. Nevertheless, the diversity and complexity of the conserved domain of the gene caused inconsistencies in these identification results. There is still a lack of drought-responsive expression patterns and functional studies of R2R3-MYB transcription factors in species. In this study, we identified a total of 210 genes in the genome, of which 207 genes were unevenly distributed across all 19 chromosomes. These poplar genes were phylogenetically divided into 23 subgroups. Collinear analysis demonstrated that the poplar genes underwent rapid expansion and that whole-genome duplication events were a dominant factor in the process of rapid gene expansion. Subcellular localization assays indicated that poplar R2R3-MYB TFs mainly played a transcriptional regulatory role in the nucleus. Ten genes were cloned from × cv. Nanlin895, and their expression patterns were tissue-specific. A majority of the genes showed similar drought-responsive expression patterns in two out of three tissues. This study provides a valid cue for further functional characterization of drought-responsive genes in poplar and provides support for the development of new poplar genotypes with elevated drought tolerance.