Objective Our objective was to explore the key genes and the molecular mechanism during the infection of Colletotrichum gloeosporioides, which could provide new insights into the genetic basis on poplar defense pathways.

Method The healthy poplar (Populus tomentosa LM50) leaves was inoculated with C. gloeosporioides. The dynamic changes of antioxidase activities of poplar leaves and key genes in the plant-interaction pathway were investigated by physiological and biochemical assays and high-throughput transcriptome sequencing.

Result Malondialdehyde (MDA) content, polyphenol oxidase (PPO) activity, superoxide dismutase (SOD) activity and catalase (CAT) activity in poplar leaves were increased at 6 days after inoculation. A total of 4 547 differential genes were screened between healthy and infected leaves, among which 2 262 were up-regulated and 2 285 were down-regulated. The differential expression genes were distributed in many functional categories, including sugar, lipid, secondary metabolite, glutathione, phenylpropanoid, amino acid, unsaturated fatty acids metabolites and so on. A large number of transcription factors were detected to be activated during the infection, such as 27 WRKY, 23 ERF, suggesting that transcription factors play important roles in response to pathogen stress. During the infection, the reactive oxygen species may act as signals that modulate the activating of plant stress responses and disease resistance pathways. The results were further confirmed by real-time quantitative PCR of six differential expressed genes detected by RNA-seq, despite differences in magnitude.

Conclusion The above results uncovered several essential genes that may play crucial roles in response to biotic stress. Pathways of glutathione, phenylpropanoid and flavonoid biosynthesis may also be activated during the infection.