Objective G2-like (Golden 2-Like/GLK) transcription factors, as important members of GARP superfamily in MYB-like transcription factors, play a key role in plant growth and development. This study aims to explore the function of PdaGLK1 gene in salt stress response of Populus davidiana × Populus alba var. pyramidalis, so as to lay a theoretical foundation for revealing the molecular regulatory mechanism of salt tolerance in Populus davidiana × P. alba var. pyramidalis and provide key candidate gene resources for stress-resistant molecular breeding of forest trees.

Method Stably transformed overexpression and repression expression plants of Populus davidiana × P. alba var. pyramidalis with the PdaGLK1 gene were obtained by Agrobacterium-mediated leaf disc method. Under NaCl stress conditions, the phenotypic changes of each line were observed, and histochemical staining and determination of stress-resistant physiological indexes were carried out for each line to explore the function of PdaGLK1 gene in salt stress response of Populus davidiana × P. alba var. pyramidalis from the aspects of phenotype, reactive oxygen species (ROS) scavenging capacity, and cell integrity.

Result (1) Two overexpression lines (OE1, OE2) and two repression expression lines (IE1, IE2) of PdaGLK1 gene were obtained through resistance screening and PCR identification. The qRT-PCR results showed that gene expression levels of OE1, OE2 were 25.16 and 24.79 times of wild type, respectively, and the gene expression levels of IE1, IE2 were 12.85% and 11.92% of wild type. (2) After NaCl stress treatment, the growth of Populus davidiana × P. alba var. pyramidalis with repressed expression of PdaGLK1 was severely inhibited, with yellowing, wilting, and shedding of leaves, and the decrease in fresh mass was significantly greater than wild type; while the overexpressed Populus davidiana × P. alba var. pyramidalis was not significantly inhibited in growth, and the decrease in fresh mass was lower than wild type and repression expression plants, indicating that the expression of PdaGLK1 gene can enhance salt stress tolerance of Populus davidiana × P. alba var. pyramidalis. (3) Under salt stress, the overexpressed Populus davidiana × P. alba var. pyramidalis plants with PdaGLK1 gene had less ROS accumulation, higher antioxidant enzyme activities than the wild type and repression expression plants, and lower malondialdehyde (MDA) content and relative electrical conductivity than wild type and repression expression plants, with reduced cell damage.

Conclusion The PdaGLK1 gene can improve salt stress adaptability of Populus davidiana × P. alba var. pyramidalis by enhancing in vivo ROS scavenging capacity, reducing cell damage, and maintaining cell integrity. This study not only provides an important basis for analyzing the function of PdaGLK1 gene in Populus davidiana × P. alba var. pyramidalis, but also provides key candidate gene resources for the innovation and improvement of salt-tolerant germplasm resources of Populus davidiana × P. alba var. pyramidalis.