The roles of OPEL homologs from Phytophthora parasitica in plant responses

A previous study indicates OPEL is a novel elicitor, which induce cell death, reactive oxygen species (ROS) accumulation, callose deposition, PAMP-triggered immunity (PTI), and systemic acquired resistance (SAR) on Nicotiana tabacum. In this study, we focus on OPEL homologous genes to verify whether OPEL is a pathogen-associated molecular pattern (PAMP) or not. Phylogenetic analysis OPEL homologous genes by tblastn search on NCBI, JGI and Broad institute genome database has shown homologs of OPEL have gene duplication in oomycetes. Besides, oomycetes plant pathogens have the most copy number of OPEL homologous genes. Analysis domain conformation of OPEL homologs indicates thaumatin-like domain is a distinct domain in oomycetes plant pathogen. Phylogenetic analysis glycoside hydrolase family 16 (GH16) in Phytophthora parasitica demonstrated OPEL homologous genes are different from other GH16 genes. These study imply OPEL homologs are unique genes in oomycetes. To characterize the interaction between OPEL homologs and plants, we overexpress OPEL homologs of P. parasitica by using agroinfiltration. PPTG_17496 induces necrosis on N. benthamiana, and PPTG_16550, PPTG_17497, and PPTG_17498 induce small region cell death on N. tabacum. Both results indicate OPEL homologs are PAMPs. However, PPTG_17496 consume 10 days to establish necrosis symptoms on N. benthamiana, which may be caused by DAMP-triggered immunity (DTI) but PTI. We need further research to find out OPEL homologs induce PTI or DTI on plants.