Peony Physiological Index, Interleaf Microbial Diversity, and Transcriptome Response to Erysiphe paeoniae Infection Stress

Peony (Paeonia lactiflora Pall.), an important ornamental and medicinal plant, has been severely damaged by the prevalence of powdery mildew, affecting its cultivation and breeding. To ascertain the response mechanism of peony to powdery mildew infection, we examined the microbial diversity, the malondialdehyde (MDA) concentration, and antioxidant enzyme activities of mildly diseased leaves (DL) and healthy leaves (HL) in peony, and transcriptome sequencing in DL and HL was performed. The results showed that the MDA content rose as the degree of infection became worse, while antioxidant enzyme activities increased first and then decreased. Following the occurrence of powdery mildew, fungal community diversity decreased, whereas there was not any significant change in bacterial communities according to microbial diversity sequencing. A total of 1,187 differentially expressed genes (DEGs) were obtained from the transcriptome sequencing. Among them, 461 downregulated DEGs were mainly involved in response to multiple stress factors and protein processing in the endoplasmic reticulum, and 726 upregulated DEGs were mainly involved in ribosomal structure, sugar metabolism, lipid metabolism, protein translation, and the biosynthesis of terpenoid and polyketides. Furthermore, the pathway involved in plant–pathogen interactions and various disease-resistance transcription factors are crucial in the peony defense mechanism against powdery mildew infection. Overall, during the infection of powdery mildew, significant changes occur in the antioxidant capacity and fungal community diversity of peony leaves, while the synthesis of various proteins is also inhibited. In addition, peony may activate various defense reactions and enhance the biosynthesis of antimicrobial compounds by regulating disease-resistance transcription factors.