In plants, R2R3 MYB transcription factors (TFs) consist of one large gene family and are involved in the regulation of many developmental processes and various stresses. However, the functions of most of MYB TFs in woody plants remain unknown. Here, PtrMYB94, an R2R3 MYB TF from Populus trichocarpa, is characterized to be involved in the regulation of drought responses and abscisic acid (ABA) signaling. PtrMYB94 encodes a nuclear-localized R2R3 MYB TF. RT-PCR results showed that the PtrMYB94 transcripts were relatively abundant in leaves and stems, and were induced rapidly in response to dehydration stress. Overexpression of PtrMYB94 improved plant drought responses, suggesting that this MYB TF may functionally regulate poplar adaptability to drought stress. Furthermore, the analysis of transcriptional expression and PtrMYB94 promoter: GUS activity showed that PtrMYB94 responded to ABA induction. PtrMYB94-overexpressing plants exhibited the inhibition of seed germination compared with the wild-type (WT) control under ABA exposure condition. The ABA content was evidently increased in the PtrMYB94-overexpressing plants relative to the WT plants. In addition, transcript levels of several ABA- and drought-responsive genes, such as ABA1 and DREB2B, were up-regulated. Taken together, our results suggest that PtrMYB94 is involved in an ABA-dependent drought stress regulation in Populus.

中文翻译：

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杨树R2R3 MYB转录因子PtrMYB94与脱落酸信号协调，以提高植物的耐旱性。

在植物中，R2R3 MYB转录因子（TF）由一个大的基因家族组成，并参与许多发育过程和各种胁迫的调控。但是，大多数MYB TF在木本植物中的功能仍然未知。在这里，PtrMYB94是来自毛果杨的R2R3 MYB TF，其特征在于参与干旱反应和脱落酸（ABA）信号的调控。PtrMYB94编码核定位的R2R3 MYB TF。RT-PCR结果表明，PtrMYB94转录本在叶片和茎中相对丰富，并且在脱水胁迫下被迅速诱导。PtrMYB94的过表达改善了植物的干旱反应，表明该MYB TF可能在功能上调节杨树对干旱胁迫的适应性。此外，转录表达和PtrMYB94启动子的分析：GUS活性表明PtrMYB94对ABA诱导有反应。与ABA暴露条件下的野生型（WT）对照相比，过表达PtrMYB94的植物表现出对种子萌发的抑制作用。相对于野生型植物，过表达PtrMYB94的植物中ABA含量明显增加。此外，一些ABA和干旱反应基因，如ABA1和DREB2B的转录水平也被上调。两者合计，我们的结果表明PtrMYB94参与了胡杨中ABA依赖的干旱胁迫调控。此外，一些ABA和干旱反应基因，如ABA1和DREB2B的转录水平也被上调。两者合计，我们的结果表明PtrMYB94参与了胡杨中ABA依赖的干旱胁迫调控。此外，一些ABA和干旱反应基因，如ABA1和DREB2B的转录水平也被上调。两者合计，我们的结果表明PtrMYB94参与了胡杨中ABA依赖的干旱胁迫调控。