Effector Cpe1 secreted by Trichoderma longibrachiatum induces plant disease resistance

Trichoderma longibrachiatum SMF2 is an important biocontrol fungus that can control pathogen through a variety of mechanisms, such as competition, antibiosis, and induction of plant disease resistance. However, the effect of proteins secreted by this microorganism on plants is not well understood. Therefore, we investigated the function of the secreted protein TLCpe1(Cpe1), which is homologous to cerato-platanin-like effector, by constructing gene knockout mutants and analyzing their phenotypes. After transforming the knockout vector of gene TLCPE1 (CPE1) into the protoplast of T. longibrachiatum SMF2, a mutant ΔCPE1 was identified. The results of PCR and southern blotting confirmed that the vector was inserted into the genome by single exchange of the upstream recombination arm, resulting in the disruption of integrity gene. RT-PCR demonstrated that CPE1 gene was not normally transcribed in the ΔCPE1 mutant. Phenotypic analysis revealed that the growth rate and spore yield were reduced in ΔCPE1. However, ΔCPE1 showed no significant difference in inhibitory activity against B. cinerea compared to the wild type of T. longibrachiatum SMF2 (WT). Root inoculation assays showed that when T. repens were treated with a spore suspension of the mutant ΔCPE1, the induced resistance of plant to B. cinerea was reduced compared to that treated with the WT. Further analysis indicated that T. repens treated with a WT spore suspension exhibited significantly higher levels of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity than plants treated with ΔCPE1, while the content of malondialdehyde (MDA) in T. repens treated with the WT was relatively low. These findings indicate that the secreted protein Cpe1 functions as an effector that enhances host resistance during the biocontrol process of T. longibrachiatum SMF2.