The role of OPEL, a secretory protein of Phytophthora parasitica, involved in induction of plant immunity

• Main Authors: Yi-Hsuan Chang, 張怡萱
• Other Authors: 劉瑞芬
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/19096523308409266776

碩士 === 國立臺灣大學 === 植物病理與微生物學研究所 === 101 === The genus Phytophthora includes more than 100 species, with many of them notorious pathogens of economically important crops. Interaction between Phytophthora pathogens and plant hosts involves the exchange of complex molecular signals from both sides. Recent studies in Phytophthora have led to the identification of some pathogen-associated molecular patterns (PAMPs) as well as many avirulence effectors, which are known to elicit PAMP-triggered immunity (PTI) and effector-triggered immunity (ETI), respectively. However, there are still numerous putative effectors with unknown function. In this study, we report the functional characterization of OPEL, a secretory protein of Phytophthora parasitica, which contains a signal peptide in the N-terminus and three other conserved domains including a thaumatin-like domain (Thau), a glycine-rich domain (GR), and a glycosyl hydrolase domain (GH). Homologs of OPEL were identified only in Oomycetes, including Phytophthora spp., Albugo, Hyaloperonospora arabidopsidis, and Pythium but not fungi and other organisms. Analysis by quantitative reverse transcriptase-PCR indicated that OPEL is expressed throughout development of P. parasitica, but is especially highly induced following the infection on plant. To characterize its function, we obtained OPEL recombinant proteins from E. coli. Infiltration of the recombinant protein into leaves of tobacco (Nicotiana tabacum) resulted in callose deposition, production of reactive oxygen species (ROS), and induced expression of salicylic acid-responsive defense genes. Moreover, when the systemic leaves of the OPEL-treated tobacco plants were challenged with Tobacco mosaic virus (TMV), the number of local lesions caused by TMV infection was significantly reduced compared to the control plants. To identify conserved domain(s) which is involved in elicitation of plant immunity, we obtained recombinant proteins representing Thau, GR, GH, or GR+GH, respectively, from E. coli and analyze their activity. The results showed that GH and GR+GH could induce callose deposition and ROS production in a level similar to those induced by OPEL recombinant protein. These results demonstrate the unique characteristics of OPEL which can induce plant defense response and systemic resistance in tobacco. Moreover, the glycosyl hydrolase domain plays an essential role for OPEL to elicit plant immunity.