Pe STZ 1, a C2H2‐type zinc finger transcription factor from Populus euphratica , enhances freezing tolerance through modulation of ROS scavenging by directly regulating Pe APX 2

Summary In the present study, Pe STZ 1 , a cysteine‐2/histidine‐2‐type zinc finger transcription factor, was isolated from the desert poplar, Populus euphratica , which serves as a model stress adaptation system for trees. Pe STZ 1 was preferentially expressed in the young stems and was significantly up‐regulated during chilling and freezing treatments. Pe STZ 1 was localized to the nucleus and bound specifically to the Pe APX 2 promoter. To examine the potential functions of Pe STZ 1 , we overexpressed it in poplar 84K hybrids ( Populus alba  ×  Populus glandulosa ), which are known to be stress‐sensitive. Upon exposure to freezing stress, transgenic poplars maintained higher photosynthetic activity and dissipated more excess light energy (in the form of heat) than wild‐type poplars. Thus, Pe STZ 1 functions as a transcription activator to enhance freezing tolerance without sacrificing growth. Under freezing stress, Pe STZ 1 acts upstream of ASCORBATE PEROXIDASE 2 ( Pe APX 2 ) and directly regulates its expression by binding to its promoter. Activated Pe APX 2 promotes cytosolic APX that scavenges reactive oxygen species ( ROS ) under cold stress. Pe STZ 1 may operate in parallel with C‐ REPEAT ‐ BINDING FACTORS to regulate COLD ‐ REGULATED gene expression. Moreover, Pe STZ 1 up‐regulation reduces malondialdehyde and ROS accumulation by activating the antioxidant system. Taken together, these results suggested that overexpressing Pe STZ 1 in 84K poplar enhances freezing tolerance through the modulation of ROS scavenging via the direct regulation of Pe APX 2 expression.