Polygalacturonase-inhibiting proteins (PGIPs) are extracellular proteins that belong to the leucine-rich repeat (LRR) protein super-family. PGIPs inhibit fungal polygalacturonases (PGs) and promote accumulation of oligogalacturonides, which activate plant defense responses. PGIPs play important roles in resistance to infection of pathogens. In this study, reverse transcriptase-polymerase chain reac-tion (RT-PCR) and RNA ligase-mediated rapid amplification of cDNA ends (RLM-RACE) were used to isolate the full-length PGIP cDNA from Populus deltoides (GenBank accession no. of PdPGIP2 and PdPGIP4: EF684913 and EF684912). Domain analysis revealed that the deduced amino acid sequences of PdPGIP2 and PdPGIP4 had a typical PGIP topology. Phylogenetic analysis of known PGIPs indicated that the two PdPGIPs were clustered to the defense-related PGIP clade. Using real-time RT-PCR, the expression patterns of the two PdPGIPs following treatment with a fungal pathogen and defense-related signaling molecules were studied. The expression levels of PdPGIP2 and PdPGIP4 were both up-regulated when inoculated with the phytopathogenic fungus Marssonina brunnea. Therefore, it was proposed that the two PGIPs might be involved in the resistance to Marssonina brunnea in P. deltoides. Polygalacturonase-inhibiting proteins (PGIPs) are extracellular proteins that belong to the leucine-rich repeat (LRR) protein super-family. PGIPs play fungal polygalacturonases (PGs) and promote accumulation of oligogalacturonides, which activate plant defense responses. PGIPs play important roles in resistance to infection of pathogens. In this study, reverse transcriptase-polymerase chain reac- tion (RT-PCR) and RNA ligase-mediated rapid amplification of cDNA ends (RLM- RACE) were used to isolate the full- length PGIP cDNA from Populus Phylogenetic analysis of known PGIPs indicated that the two PdPGIPs were clustered to the defense (GenBank accession no. of PdPGIP2 and PdPGIP4: EF684913 and EF684912). Domain analysis revealed that the deduced amino acid sequences of PdPGIP2 and PdPGIP4 had a typical PGIP topology. -related PGIP clade. Using real-time RT-PCR, the expression patterns of the two PdPGIPs following treatment with a fungal pathogen and defense-related signaling mo The expression levels of PdPGIP2 and PdPGIP4 were both up-regulated when inoculated with the phytopathogenic fungus Marssonina brunnea. Thus, it was proposed that the two PGIPs might be involved in the resistance to Marssonina brunnea in P. deltoides.