Genome-wide identification of the WOX gene family in Populus davidiana×P.bolleana and functional analysis of PdbWOX4 in salt resistance.

WOX transcription factors (TFs) are plant specific transcription regulatory factors that have a momentous role in maintaining plant growth and development and responding to abiotic stress. In this study, a total of 13 PdbWOX genes were identified. qRT-PCR analyses showed that 13 PdbWOX genes were responsive to salt stress. Notably, the expression of PdbWOX4 was significantly changed at all time points under NaCl stress, suggesting that PdbWOX4 expression may be involved in salt stress. Further, an overexpression vector of PdbWOX4 was constructed and transient transformed into Shanxin poplar. Biochemical staining and physiological parameter analysis showed that overexpression of PdbWOX4 decreased the total antioxidant capacity (T-AOC) and peroxidase (POD) activity, which in turn reduced the scavenging capacity of reactive oxygen species (ROS), and increased the cell damage and death induced by salt stress. qRT-PCR and ChIP-PCR demonstrated that PdbWOX4 can regulate the expression of PdbDREB2C by binding to its promoter. Further analyses revealed that overexpression of PdbDREB2C can reduce cellular damage by increasing ROS scavenging capacity thereby improving salt tolerance in Shanxin poplar. Taken together, we found that PdbWOX4 negatively regulated the salt tolerance of Shanxin poplar by repressing the PdbDREB2C, suggesting that PdbWOX4 may play a key role in the tolerance of Shanxin poplar to salt stress, and is an important candidate gene for molecular resistance breeding in forest trees.