Overexpression of a <Emphasis Type="Italic">Populus euphratica CBF4</Emphasis> gene in poplar confers tolerance to multiple stresses

C-repeat binding factors (CBFs) play a key role in abiotic stresses. However, little is known about CBFs in Populus euphratica. Here, we isolated PeCBF4a, a member of CBF gene family from P. euphratica. Its expression was induced by dehydration, salinity and low temperature. We generated transgenic poplars (Populus tomentosa ‘YiXianCiZhu B385’) overexpressing PeCBF4a (OE-PeCBF4a) under the control of the CaMV 35S promoter or transformed with empty vector. The wild-type (WT) and empty vector lines were used as controls. Under abiotic stresses, the photosynthetic rate (Pn) of 60-day-old OE-PeCBF4a lines increased 34.7–165.7?% and the instantaneous water use efficiency (iWUE) increased 48.9–103.7?% over controls. The maximum quantum efficiency of PSII photochemistry (Fv/Fm) values in PeCBF4a-overexpressing lines did not change significantly and were 2.14–5.89?% higher. The non-photochemical quenching coefficient (NPQ) mean of OE-PeCBF4a lines decreased by 12.02–23.64?% while the photochemical quenching (qP) value was 8.75–22.31?% higher than controls. OE-PeCBF4a lines also displayed higher superoxide dismutase (SOD) activities and markedly lower malondialdehyde (MDA) levels compared to controls. Higher levels of proline and sugars accumulated in transgenic plants. Overexpression of PeCBF4a not only induced strong expression of the stress-responsive downstream target genes of PeCBF4a, PtRCI2A (rare-cold-inducible 2A) and PtDI21 (drought-induced 21), but also caused dwarfed phenotypes. Based on results from P-V curve measurements, the osmotic adjustment capability of OE-PeCBF4a plants was enhanced. These results confirmed that OE-PeCBF4a poplars exhibit greater tolerance to stress, indicating that PeCBF4a plays a positive role in stress tolerance.