LsGRP1誘導阿拉伯芥系統性抗病之傳訊路徑探討

植物會因應病原菌侵擾而活化先天性免疫，受到侵擾的組織會累積水楊酸(salicylic acid, SA)並長距離傳訊，啟動系統性誘導抗病反應(systemic acquired resistance, SAR)。LsGRP1為介導葵百合抗百合灰黴病的關鍵防禦蛋白，內源性表現及外源性施用LsGRP1皆可有效抑制處理葉及系統葉百合灰黴病的病徵，指出LsGRP1除了誘導原位抗性也具有誘導植物系統性抗病的能力，然其機制仍有待釐清。前人研究發現阿拉伯芥葉片表現LsGRP1可提升病原菌入侵後所誘導的防禦反應，而本研究進一步觀察外源性大腸桿菌生產之融合蛋白SUMO-LsGRP1△SS的作用，發現其可促使阿拉伯芥葉片提升由flg22激活的免疫反應；在系統葉上可減少Pseudomonas syringae pv. tomato (Pst) DC3000的增殖菌量及增加flg22誘發的癒傷葡聚醣沉積。經試驗得知SUMO-LsGRP1△SS之部分區段刪除突變的誘導系統性抗病強度皆較SUMO-LsGRP1△SS者為低。藉由阿拉伯芥誘導系統性抗病的水楊酸依賴型傳訊路徑(SA-dependent signaling pathway)之sid2 (SA induction deficient 2)、bsmt1 (benzoic acid/SA carboxyl methyltransferase 1)突變株及2-哌啶甲酸依賴型傳訊路徑(pipecolic acid-dependent signaling pathway) 之ald1 (AGD2-like defense response protein 1)、sard4 (SAR-deficient 4)突變株分析比較SUMO-LsGRP1△SS誘導系統葉抗Pst DC3000的強度，得知這兩型傳訊路徑皆參與LsGRP1誘導系統性抗病之發生，且SUMO-LsGRP1△SS可提升水楊酸依賴型傳訊路徑之SID2及BSMT1基因及2-哌啶甲酸依賴型傳訊路徑之ALD1及SARD4基因的表現量，確認LsGRP1在阿拉伯芥處理葉激活這兩型系統性抗病傳訊路徑。綜合言之，LsGRP1可以誘導處理葉及系統葉產生抗病反應，且經由水楊酸及2-哌啶甲酸依賴型傳訊路徑啟動系統性抗病的表現，此等研究為LsGRP1之植物保護應用發展建立了重要的學理基礎。

關鍵字

LsGRP1 ；阿拉伯芥；系統性抗病；水楊酸依賴型傳訊路徑； 2-哌啶甲酸依賴型傳訊路徑

並列摘要

Plant activates innate immunity in response to pathogen attack. The challenged tissues accumulate salicylic acid (SA) and conduct long-distance signaling to activate systemic acquired resistance (SAR). LsGRP1 is a key defense protein mediating lily resistance to gray mold. Endogenous expression and exogenous application of LsGRP1 suppress gray mold symptom in not only treated but also systemic leaves of Lilium spp, indicating that LsGRP1 enables the activation of plant systemic resistance besides in situ; however, the underlying mechanism remains unclear. Previous studies showed that LsGRP1-transgenic Arabidopsis could enhance defense responses post pathogen attack. In this study, LsGRP1 enhancing flg22-triggered defense responses in Arabidopsis post SUMO-LsGRP1△SS treatment was demonstrated; moreover, a reduction of the population of Pseudomonas syringae pv. tomato (Pst) DC3000 and an increase of flg22-triggered callose deposition in the systemic leaves were shown. The partial deletions of SUMO-LsGRP1△SS exhibited lower systemic protection than SUMO-LsGRP1△SS did. The assays on SA-dependent signaling pathway sid2 (SA induction deficient 2), bsmt1 (benzoic acid/SA carboxyl methyltransferase 1) mutants and pipecolic acid (Pip)-dependent signaling pathway ald1 (AGD-like defense response protein 1), sard4 (SAR-deficient 4) mutants of Arabidopsis showed that the proliferation of Pst DC3000 could not be reduced by SUMO-LsGRP1△SS treatment. Besides, the gene expression of SID2 and BSMT1 (SA-dependent signaling pathway), ALD1 and SARD4 (Pip-dependent signaling pathway) increased in Arabidopsis leaves after SUMO-LsGRP1△SS treatment, indicating both signaling pathways were activated by LsGRP1 for systemic resistance induction of Arabidopsis against Pst DC3000. In conclusion, LsGRP1 can induce local and systemic resistance to Pst DC3000, and SA and Pip-dependent signaling pathways are involved in the activation of systemic acquired resistance in model plant Arabidopsis, which become the knowledge base for LsGRP1 application in plant protection.