番茄與印度梨形孢菌之共生與誘導番茄系統性抗病之研究

Abstract

印度梨形孢菌 (Piriformospora indica) 為宿主範圍極廣且具高農業應用價值之植物共生真菌。我們先前研究發現 P. indica 感染番茄與菸草根部後會誘導系統性防禦 (induced systemic resistance，簡稱ISR) 以抗多種根部與葉部病菌，而 RNA-seq 分析結果顯示番茄根部接種 P. indica 後之感染初期會調控植物代謝、賀爾蒙及逆境訊息傳導以利進行共生，且 P. indica 之數個效應蛋白質會影響番茄病害防禦，然而其中具體分子機制仍需進一步釐清。本研究以錐藍染色法觀察番茄感染 P. indica 後不同天數之根部，以解析此菌與番茄之共生階段。轉錄分析結果顯示 P. indica 感染初期會誘導番茄根部之乙烯 (ethylene, ET)、水楊酸 (salicylic acid, SA) 及茉莉酸 (jasmonic acid, JA) 訊息路徑，共生晚期則持續促進番茄根部 ET 訊息路徑以利維持共生，且促進葉部 JA 訊息路徑產生。在共生早期 RLP6、ETR4、ETR6 及 NPL93 在番茄根部之轉錄表現會被誘導，且番茄全株性短暫靜默試驗所得結果指出，這些基因可能是藉由正調控 JA 與 SA 訊息路徑而參與對抗葉部病原菌 Botrytic cinerea (Bc) 與 Pectobacterium carotovorum subsp. carotovorum (Pcc) 之防禦反應，且 RLP6 為 P. indica 之共生正向調控者。此外，針對六個 P. indica 之效應蛋白質基因的分析結果顯示，這些基因在共生不同時期具特異性表現，且依病害防禦反應與訊息路徑分析結果推論 PIIN_04363 、PIIN_07152 及 PIIN_09643 可能參與削減植物免疫反應之效應。本研究所得研究結果闡明P. indica 與番茄共生以及誘導 ISR 之關鍵訊息路徑與重要調控因子，預期應有助於未來進一步之基礎科研與農技應用發展。

Piriformospora indica is a root endophytic fungus that can establish mutual symbiosis with a wide range of plants and therefore promotes growth and stress tolerance in hosts. Our previous studies showed that P. indica colonization promoted tomato and Nicotiana benthamiana defense against distinct important bacterial, fungal and oomycete pathogens by triggering induced systemic resistance (ISR). RNA-seq analysis of P. indica-infected tomato roots revealed that plant metabolisms and hormone/stress signaling pathways were significantly modulated to promote Pi colonization. In addition, expression of several P. indica effectors in tomato lessened disease tolerance. However, the underlying mechanisms remained to be determined. This study firstly dissected the stages of symbiosis between tomato root and P. indica. Transcriptional analyses in tomato roots showed that ethylene (ET), salicylic acid (SA) and jasmonic acid (JA) signaling pathways were up-regulated at the early stage of symbiosis, and the continuous up-regulation of ET signaling pathway at the late stage may be involved in the maintenance of symbiosis. Transcriptional analyses in tomato leaves showed that JA signaling pathway was up-regulated at the late stage of symbiosis. Temporal RT-qPRC analysis on tomato root confirmed that expression of four tomato genes (ETR4, ETR6, RLP6 and NPL93) was upregulated at early stages of symbiosis. Functional genetic study by transient systemic silencing suggested that these genes are involved in tomato defense against Botrytic cinerea (Bc) and Pectobacterium carotovorum subsp. carotovorum (Pcc) by positively regulating JA and SA signaling pathways, and RLP6 could be a positive regulator of symbiosis. Furthermore, six P. indica effectors were found to be differentially expressed at different symbiosis stages. Analyses of disease responses and the involved signaling pathways suggested that PIIN_04363, PIIN_07152 and PIIN_09643 might be involved in the suppression of plant immunity. This study provides important information on the signaling pathways and key regulators involved in the symbiosis and ISR in tomato-P. indica interaction. These and future work may benefit the development of further studies and agricultural applications.