Abstract
The MYB, one of the largest transcription factor families in plants, is related to various biological processes. For an example, the R2R3-MYB family plays an important role in regulation of primary and secondary metabolism, plant growth and development, and responses to hormones and stresses. However, functional studies on the poplar R2R3-MYB genes are limited. In this study, we identified 207 poplar R2R3-MYB genes that are unevenly distributed on the 19 chromosomes of poplar, followed by characterization of their conserved domains. On the basis of phylogenetic analysis, these genes can be divided into 23 groups. Evidence from synteny analyses indicated that the poplar R2R3-MYB gene family is featured by tandem and segmental duplication events. On the basis of RNA-Seq data, we investigated salt responsive genes and explored their expression patterns. Furthermore, we cloned the PsnMYB108 gene from poplar, which is significantly up-regulated in roots and leaves in response to salt stress. To validate its function, we developed transgenic tobacco plants that over-express the PsnMYB108 gene. It appears that the transgenic lines are more tolerant to salt stress than the wild type does. Evidence from physiological analyses demonstrated that over-expression of PsnMYB108 may improve tobacco salt stress tolerance by increasing the reactive oxygen species scavenging ability and the accumulation of proline. These results laid the foundation for future analysis and functional studies of poplar R2R3-MYB family members, and revealed that PsnMYB108 plays an important role in improving plant salt stress tolerance.
Highlights
The MYB gene family is widely existed in eukaryotes and has multiple functions
In order to further verify the function of the genes we identified, we chose the PsnMYB108 gene, which was significantly up-regulated in both roots and leaves under salt stress, for clone and genetic transformation
We focused on 207 poplar R2R3-MYB family members, starting with conserved domain characterization, phylogenetic analysis, chromosome distribution and collinearity analysis, and we explored the tissue differential expression patterns and salt stress response of these genes, using RNA-Seq data
Summary
The MYB gene family is widely existed in eukaryotes and has multiple functions. Since its first discovery in avian myeloblastosis virus in 1982 (named as v-myb) (Klempnauer et al, 1982), many members from the family have been identified. Poplar R2R3-MYB Gene Family proteins known as transcription factors that harbor MYB domains. This domain often contains 1 to 4 incompletely repeating amino acid sequence repeats (R). There are regularly spaced tryptophan (W) residues in each R sequence, in order to form a helix–turn–helix (HTH) structure hydrophobic core with the second and third helix (Kanei-Ishii et al, 1990; Dubos et al, 2010). Sometimes tryptophan residues are replaced by some hydrophobic amino acids. The first tryptophan residue in the R3 repeat in plants is often replaced by leucine, isoleucine, or phenylalanine (Martin and Paz-Ares, 1997). The third helix of each repeat is the “recognition helix,” which directly contacts DNA and inserts into the main groove (Jia et al, 2004)
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