Table_2_Characterization of the Poplar R2R3-MYB Gene Family and Over-Expression of PsnMYB108 Confers Salt Tolerance in Transgenic Tobacco.DOC

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.

MYB转录因子家族（MYB transcription factor family）是植物中规模最大的转录因子家族之一，与多种生物学过程密切相关。例如，R2R3-MYB家族在初生代谢与次生代谢、植物生长发育以及激素和胁迫响应的调控中发挥关键作用。然而，当前关于杨树R2R3-MYB基因的功能研究仍较为匮乏。本研究共鉴定得到207个杨树R2R3-MYB基因，这些基因不均匀分布于杨树的19条染色体上，随后对其保守结构域进行了系统表征。基于系统发育分析（phylogenetic analysis），这些基因可被划分为23个进化组。共线性分析（synteny analysis）结果显示，杨树R2R3-MYB基因家族的主要进化特征为串联重复（tandem duplication）和片段重复（segmental duplication）事件。基于RNA-Seq数据，本研究对盐胁迫响应基因进行了分析，并探究了其表达模式。此外，我们从杨树中克隆得到PsnMYB108基因，该基因在盐胁迫下的根系和叶片中显著上调表达。为验证该基因的功能，我们构建了过表达（over-expression）PsnMYB108的转基因烟草植株。结果表明，转基因株系相较于野生型（wild type）烟草对盐胁迫具有更强的耐受性。生理分析证实，过表达PsnMYB108可通过提升烟草的活性氧（reactive oxygen species）清除能力与脯氨酸（proline）积累量，增强其盐胁迫耐受性。本研究结果为后续杨树R2R3-MYB家族成员的功能与进化分析奠定了基础，同时揭示了PsnMYB108在提升植物盐胁迫耐受性方面的重要作用。