阿拉伯芥熱休克因子HSFC1在非生物逆境反應與生長之功能性研究

Abstract

熱休克反應是生物面對高溫逆境時所產生的一種防禦機制，可藉由熱休克轉錄因子調控熱休克蛋白的生成來保護細胞。在阿拉伯芥共有21個熱休克轉錄因子，分為A、B和C三類群，約有一半的熱休克轉錄因子參與在熱休克反應的訊息傳導中，其中以A類群被認為和激活熱休克反應有關，B類群扮演負向調控的角色以終止熱休克反應，而C類群則只有一個 (HSFC1)。過去的研究指出，在其他物種的熱休克轉錄因子C類群是參與在鹽分與乾旱逆境當中，然而，阿拉伯芥的HSFC1功能目前仍然未知。我們先前的研究發現，阿拉伯芥HSFC1表現會受到鹽分與離層酸誘導，並參與離層酸訊號傳遞路徑。在本次的研究中，我建立具不同的功能性的HSFC1轉殖株：HSFC1-overexpression (OE)， -VP16及-SRDX，研究其功能。結果顯示，HSFC1表現會受到低溫誘導，不受高溫影響。我發現經過熱處理後，HSFC1-OE，-VP16的存活率較野生型、hsfc1及-SRDX高，而經過鹽分、離層酸及甘露醇處理後種子HSFC1-OE種子萌芽率比-VP16與-SRDX低，HSFC1-OE根長比-VP16與-SRDX要來的短。此外，暫時性表現系統實驗，結果顯示HSFC1可能負向調控HSFA2、HSFA3及HSFA6b等熱休克轉錄因子活性。我的研究發現HSFC1可能參與在低溫、鹽分及乾旱逆境反應以及ABA訊息傳導路徑，而詳細調控機制則須更進一步研究。

Heat shock response (HSR) is a universal mechanism in all organisms to overcome heat stress (HS) or higher than normal temperatures. While HSR was happening, the accumulation of heat shock proteins (HSPs) would protect cells from HS and this mechanism is controlled by heat shock factors (HSFs). The Arabidopsis HSF family contains 21 members; about half are involved in the signaling cascade of HSR. Some Arabidopsis HSFs are well-studied, for example, the class A HSF are considered to amplify or sustain the expression of HSPs because of containing activation domain; the class B lacks a typical activation domain, are considered to attenuated HSR. There has only one HSF in class C in Arabidopsis. Although HSFCs have been found to be involved in salt and drought stress in other plants, the function of HSFC1 in Arabidopsis has remained unknown. In our previous study, we found that HSFC1 could be induced by salt and ABA and the expression of HSFC1 was altered in ABA-deficient and ABA-insensitive mutants, indicated that ABA signaling is required for proper HSFC1 expression. In this study, T-DNA-insertional mutant and HSFC1-overexpression (OE), -VP16, and -SRDX plants were used for a functional study of the HSFC1 in response temperature stress and during various developmental stages. My study showed that the expression of HSFC1 was induced by cold stress not by heat stress. At the same time, I found that HSFC1-OE and HSFC1-VP16 plants were more heat tolerant phenotype under acquired thermotolerance assay. In seed germination test, I concluded that HSFC1-OE shows higher sensitive to salt, ABA and mannitol compared with the HSFC1-VP16 and HSFC1-SRDX seedlings. In root length assay, I concluded that HSFC1-OE also shows more sensitive to salt, ABA and mannitol compared with the HSFC1-VP16 and HSFC1-SRDX seedlings. Finally, in protoplast transactivation assay, I found that the ectopic expressed HSFC1 had negative effect on HSFA2, HSFA3 and HSFA6b in stress-responsible maker gene HSP18.2 induction. My research concluded that HSFC1 was induced by cold, salt and drought stress via ABA signaling pathway. We will research more regulation mechanisms about HSFC1 in the future.