Comprehensive genome-wide analyses of R2R3-MYB transcription factors and tolerance to drought stress in Populus davidiana x Populus bolleana

The MYB family is one of the largest families of transcription factors, in which the R2R3-MYB subgroup plays a crucial role in various biological processes. R2R3-MYBs in Populus davidiana x Populus bolleana have, however, not been systematically investigated. Here, based on the gene annotation of P. davidiana x P. bolleana genome sequence, all PdbR2R3-MYB transcripts were identified. These PdbR2R3-MYBs were classified into 29 subgroups (C2 to C30) according to the phylogenetic analysis of Arabidopsis thaliana AtR2R3-MYBs. The analysis of gene structures and protein motifs showed the conservation and evolution of PdbR2R3-MYBs. The cis-acting elements in the promoters of PdbR2R3-MYB genes were predicted, and the results indicated an abundance of abscisic acid and defense- and stress-responsive elements. The results of qRT-PCR revealed that nine PdbR2R3-MYB genes were differentially expressed in various tissues and can be regulated by drought stress; thus, these genes may play key roles in the response of plants to drought stress. In addition, the expression of PdbMYB5 and PdbMYB102 was significantly higher than those of the other seven MYB genes; hence, PdbMYB5 and PdbMYB102 overexpressing (OE) and silenced (SE) poplar plants were generated to investigate drought stress tolerance. The PdbMYB5 and PdbMYB102 OE plants showed enhanced reactive oxygen species scavenging capability, less cell damage, and high expression levels of the SOD and POD genes, whereas the SE plants showed the opposite results, thus suggesting that PdbMYB5 and PdbMYB102 conferred enhanced drought tolerance to the plants. This study provided insights into gene characterization, structure, evolution, expression, and function of the PdbR2R3-MYB family in poplar plants.