Objective This paper aims to provide genetic resources and resistant germplasm for tree resistance breeding by analyzing the disease-resistance function of encoding gene PdbGSTU for glutathione S-transferase in Populus davidiana × P. bolleana.

Method PdbGSTU was cloned in P. davidiana × P. bolleana by PCR, and bioinformatics analysis were analyzed. The tissue specific expression patterns and expression patterns induced by plant hormones of PdbGSTU were also analyzed by RT-qPCR. Overexpressing/sciencing PdbGSTU plants of P. davidiana × P. bolleana obtained through transgenic technology and function of PdbGSTU on disease resistance were verified by observing and comparing the phenotypes and concurrent lesion areas of leaves after inoculation with Alternaria alternata. Moreover, the contents of H₂O₂ and the activities of antioxidant enzyme were measured in leaves before and after A. alternata inoculation.

Result (1) The open reading frame (ORF) length of PdbGSTU was 753 bp, which encoded 250 amino acids with the protein relative molecular mass 29.01 kDa. The PdbGSTU was a stable hydrophilic acidic protein located in the cytoplasm. Systematic evolutionary analysis revealed that PdbGSTU in P. davidiana × P. bolleana had a close relationship with KAJ6918316 in P. alba × P. berolinensis. The analysis of cis-acting elements in promoter sequence of PdbGSTU showed that, this sequence contained multiple cis-acting elements related to plant response to stress or phytohormones. (2) RT-qPCR showed that PdbGSTU had the highest expression level in apical bud of P. davidiana × P. bolleana, and the lowest expression level in root. In addition, PdbGSTU could response to MeJA, SA and ACC, and show up-regulated expression. (3) After inoculation with A. alternata, the lesion areas on the leaves of wild-type and PdbGSTU gene suppressed P. davidiana × P. bolleana were 6.42 and 16.46 mm², respectively. However, on the leaves of plants overexpressing PdbGSTU gene, a small number of inoculation sites showed obvious lesions, while the rest of inoculation sites only showed fading.

Conclusion PdbGSTU is positively involved in the resistance process of P. davidiana × P. bolleana to A. alternata infection, and can enhance the resistance of P. davidiana × P. bolleana to pathogens by clearing reactive oxygen species.