探討印度梨形孢菌效應蛋白與番茄組蛋白去乙醯酶參與番茄初級免疫反應之角色

Abstract

Pattern-triggered immunity (PTI) 是一種植物為了抵抗微生物而引起的廣效初級免疫反應。有益真菌 Piriformospora indica 藉由茉莉酸 (JA) 信號傳導抑制阿拉伯芥 PTI 反應並與其共生。本研究室先前發現 P. indica 與番茄共生過程中，植物根部的賀爾蒙訊息傳遞路徑調節與阿拉伯芥的調控機制非常相似。P. indica 表現多種效應蛋白質會促進其在番茄根系的共生。先前研究顯示在不同共生階段差異表現之兩種 P. indica 效應蛋白質 PIIN_09643 與 PIIN_04363 會降低植物防禦反應。本研究第一個目的是闡明 PIIN_09643 與 PIIN_04363 對番茄 PTI 反應的影響。結果顯示，在共生後期表達的PIIN_04363 能夠強烈抑制根部癒傷葡聚醣與 H2O2 的累積，卻會促進 SlPTI5 的轉錄表現。另一方面，共生早期大量表現的PIIN_09643 則中度抑制根部癒傷葡聚醣與 H2O2 的累積，並延遲 SlPTI5的轉錄表現。此外，兩種效應蛋白質皆不會抑制本研究室所檢測的葉部 PTI 反應。然而，在植物中大量表現 PIIN_04363 會導致細胞凋亡，與抑制 JA 路徑及過量表現 PIIN_04363會增強植物對 B. cinerea 的感病性之現象具關連性。鑑於已知植物 PTI 反應亦會涉及表觀遺傳的調控，本研究第二個目是為了闡明 SlHDA3 和 SlHDA8（阿拉伯芥組蛋白去乙醯酶 AtHDA6 與 AtHDA15 之番茄同源基因）對根部 PTI 反應的影響。結果顯示 SlHDA3 為番茄根部癒傷葡聚糖累積之負向調控者與抵抗青枯病之正向調控者。相較之下，SlHDA8 對於癒傷葡聚糖累積與抵抗青枯病中可能沒有重要影響。預期以上研究結果將有助於提供番茄與微生物相互作用中PTI反應調節之研究，以確保全球糧食的生產和安全。

Pattern-triggered immunity (PTI) is a broad spectrum basal defense of plants against microbial communities. For the beneficial fungus Piriformospora indica, suppression of Arabidopsis PTI responses is regulated by JA signaling and is required for its colonization. Our previous studies showed the regulation of phytohormones signaling pathways in roots during tomato-P. indica symbiosis closely resembles that of Arabidopsis. P. indica expressed a plethora of effectors to promote root colonization in tomato. Previous studies showed that two P. indica effectors, PIIN_09643 and PIIN_04363, which are expressed at different stages of colonization reduced plant disease defense. The first aim of this study was to evaluate the effects of PIIN_09643 and PIIN_04363 on tomato PTI responses. The results showed that PIIN_04363, which is expressed at the late stage during symbiosis, strongly suppressed callose deposition and H2O2 accumulation in roots, but increased the expression of SlPTI5. On the other hand, PIIN_09643, which is highly expressed at early stages during symbiosis, moderately suppressed callose deposition and H2O2 accumulation, and delayed the expression of SlPTI5 in roots. Furthermore, both effectors did not suppress the examined PTI responses in leaves. However, overexpression of PIIN_04363 caused spontaneous cell death, which along with the repression of the JA pathway, is consistent with the enhanced susceptibility of PIIN_04363-overexpressing plants to B. cinerea. Given the known involvement of epigenetic regulation in plant PTI, the second aim of this study was to evaluate the effects of SlHDA3 and SlHDA8, the tomato homolog of Arabidopsis histone deacetylases AtHDA6 and AtHDA15, respectively, on root PTI responses. SlHDA3 was found to be a negative regulator of callose deposition in tomato roots and a positive regulator of bacterial wilt resistance. In contrast, SlHDA8 might not play an important role in callose deposition and bacterial wilt resistance. These results are expected to enrich the study on the PTI regulation in tomato-microbe interactions which are expected to ensure global food production and security.