Over-expression of the Pseudomonas syringae harpin-encoding gene hrpZm confers enhanced tolerance to Phytophthora root and stem rot in transgenic soybean
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Phytophthora root and stem rot (PRR) caused by Phytophthora sojae is one of the most devastating diseases reducing soybean (Glycine max) production all over the world. Harpin proteins in many plant pathogenic bacteria were confirmed to enhance disease and insect resistance in crop plants. Here, a harpin protein-encoding gene hrpZpsta from the P. syringae pv. tabaci strain Psta218 was codon-optimized (renamed hrpZm) and introduced into soybean cultivars Williams 82 and Shennong 9 by Agrobacterium-mediated transformation. Three independent transgenic lines over-expressing hrpZm were obtained and exhibited stable and enhanced tolerance to P. sojae infection in T2–T4 generations compared to the non-transformed (NT) and empty vector (EV)-transformed plants. Quantitative real-time PCR (qRT-PCR) analysis revealed that the expression of salicylic acid-dependent genes PR1, PR12, and PAL, jasmonic acid-dependent gene PPO, and hypersensitive response (HR)-related genes GmNPR1 and RAR was significantly up-regulated after P. sojae inoculation. Moreover, the activities of defense-related enzymes such as phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO), peroxidase, and superoxide dismutase also increased significantly in the transgenic lines compared to the NT and EV-transformed plants after inoculation. Our results suggest that over-expression of the hrpZm gene significantly enhances PRR tolerance in soybean by eliciting resistance responses mediated by multiple defense signaling pathways, thus providing an alternative approach for development of soybean varieties with improved tolerance against the soil-borne pathogen PRR.
KeywordsTransgenic plant Phytophthora sojae Harpin protein Disease resistance
This work was supported by grants from China National Novel Transgenic Organisms Breeding Project (2016ZX08004-004), Jilin Provincial Science and Technology Development Project (20150204011NY) and Jilin Provincial Agricultural Science and Technology Innovation Project (CXGC2017JQ013). We also thank Dr. Yongzhi Wang for providing the polyclonal antibodies and standard proteins.
Hongyu Pan, Yingshan Dong and Qiyun Li designed the experiments. Qian Du, Xiangdong Yang, Xiaofang Zhong and Kyung Seok Kim performed the experiments, analyzed the data and drafted the manuscript. Jing Yang and Guojie Xing conducted the Agrobacterium-mediated transformation experiments. Jinhua Zhang, Xiaoyu Li and Zhaoyuan Jiang conducted the inoculation assay. All the authors participated in the revision of the manuscript.
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Conflict of interest
The authors claim no conflict of interest in the publication of this paper.
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