近年由於溫室效應的影響，導致全球氣溫逐年攀升。植物由於無法自由遷徙，因而必須時刻面對全球暖化所帶來高溫逆境。此外，植物是人類主要糧食來源，在畜牧業也被用作飼料。是以當高溫逆境對作物的生長造成不利的影響，進而使得產量下降時，勢必也會衝擊到人類的生存繁衍。因此，瞭解植物如何抵禦高溫，進而提升作物對高溫的耐受能力，便有其重要性與迫切性。 我們以前向式遺傳學(forward genetic approach)的策略，藉由篩選熱敏感型的突變株，配合基因定位的技術，找尋植物中熱反應相關的基因，並進一步探討此基因如何保護植物的耐熱機轉，期望藉此找尋提升作物耐熱能力的方法。利用此方式，我們篩選到一株帶有熱反應性狀的突變株，將其命名為hit5 (heat intolerance 5)，此突變株對於兩種不同形式的熱逆境處理：長時間溫和高溫(prolonged heat stress)以及短時間高強度高溫(heat shock stress)有著不同的反應性狀，相對於野生型植株，對長時間溫和高溫處理失去耐受能力，然而對短時間高強度高溫處理卻具有更佳的耐受能力。根據實驗結果顯示，造成hit5突變株兩種熱反應性狀為同一個隱性基因突變造成，突變點位置位於第五條染色體At5G40280基因(或稱為ERA1, enhanced responses to ABA 1)上，造成此基因mRNA的剪切(splicing)發生缺失，因而失去正常功能。此基因編譯的蛋白質已知為法尼脂轉移酶β次單元(farnesyltransferase β subunit) ，因此hit5突變株的熱反應性狀指出了植物對於熱逆境反應的調控也發生在轉譯後修飾的部分。過去的文獻指出，hit5/era1基因的突變，會使得植株對植物賀爾蒙abscisic acid (ABA)敏感，因而推測HIT5/ERA1的法尼脂化修飾會負調控ABA訊號傳遞中的某傳訊因子。而ABA過去普遍被認為是植物逆境賀爾蒙，因此我們探討了蛋白質的法尼脂化修飾，在植物耐熱機制中所扮演的角色以及與植物賀爾蒙ABA之間是否有相互調節的關係。此外，由於hit5突變株對長時間溫和高溫以及短時間高強度高溫有著不同的反應性狀，因此推測至少有兩個以上的訊息傳遞路徑，受到法尼脂化修飾的調控。這些不同的訊息調控路徑以及參與其中的分子，是我們接續要找尋及探討的目標。根據過去文獻結果，我們鎖定兩個可能參與在其中的蛋白質AtDjA2 (At5g22060)與AtDjA3 (At3g44110)，並探究其在HIT5蛋白質所調控的熱反應機制中。 ;Heat stress from global warming has serious impacts on living organisms. Because plants are sessile organisms, they have to face the adverse effects from high temperatures which can directly influence the properties of various cellular components, even leading to cell death. Therefore, it is important to investigate the plant heat tolerance mechanisms for improving the crop resistance to high temperature. In this study, I used a forward genetic approach to screen the heat intolerant mutants of Arabidopsis to find heat stress tolerant genes in plants. The heat-intolerant 5 (hit5) was therefore isolated. This mutant exhibits two different heat response phenotypes: sensitive to prolonged heat stress but tolerance to sudden heat shock stress compared to wild type. Subsequent gene mapping identified that HIT5 is the ENHANCED RESPONSE to ABA 1 (ERA1) gene which encodes the β subunit of protein farnesyltransferase. This finding demonstrated that the plant heat stress responses (HSRs) also involve in post-translational modification. Previous studies have indicated the hit5/era1 mutant is hypersensitive to abscisic acid (ABA). In my study, I investigated the relationship between protein farnesylation, plant thermotolerance, and ABA regulation. Results indicated that the hit5/era1 mediated heat stress responses is ABA independent. Meanwhile, according to previous reports, Arabidopsis AtDjA2 (At5g22060) and AtDjA3 (At3g44110) are HIT5/ERA1 substrates. There potential roles in protein farnesylation mediated heat stress responses were studied as well.
