A salt-stress-regulator from the Poplar R2R3 MYB family integrates the regulation of lateral root emergence and ABA signaling to mediate salt stress tolerance in Arabidopsis.

The roles of most MYB transcription factors (TFs) in the poplar remain unclear. Here, we demonstrate that PtrSSR1, a salt-stress-regulator in the Populus trichocarpa R2R3 MYB gene family, mediates the tolerance of transgenic Arabidopsis plants to salt stress. The transcripts of PtrSSR1 could be induced by salt stress rapidly in poplar. Subcellular localization and yeast assays indicated that PtrSSR1 encoded a nuclear protein with transactivation activity. The Arabidopsis transformants overexpressing PtrSSR1 clearly displayed lateral root emergence (LRE) inhibition compared with wild-type (Wt) under normal conditions; while upon NaCl treatment, the transformants showed improved tolerance, and the LRs emerged faster from salt-induced inhibition. A strong correlation could exist between the LRE mediated by PtrSSR1 and abscisic acid (ABA), mainly because the transformants displayed more sensitivity to exogenous ABA during both seed germination and LRE, and had a distinctly increased level of endogenous ABA. Furthermore, several ABA- and salt-related genes, such as NCED3, ABI1 and CBL1, were up-regulated. Thus, our results suggest that elevation in the endogenous ABA content bring alteration of plant LR development, and that the poplar R2R3 MYB TF PtrSSR1 vitally improve salt stress tolerance by integrating the regulation of LRE and ABA signaling in Arabidopsis.