植物為固著型生物，是以植物演化出許多適應及抵禦環境逆境的策略，避免受其傷害。由於溫室效應，全球暖化的關係，高溫逆境成為近年來嚴重影響作物 產量的重要原因之一，因此如何提高植物耐受逆境已成為重要的課題。本實驗室 先前利用前向式遺傳學 研究法 (forward genetic approach)篩選到一棵對持續性熱 逆境及熱休克逆境敏感的突變株 heat intolerant 4 (hit4)。 後續研究發現， HIT4所 編碼的產物 位在 染色質中心上。在植物遭受熱逆境時， HIT4會 藉由染色質構 型重塑，誘使染色質中心呈 現消散狀態，促使平時靜默不轉錄 (transcriptional gene silencing, TGS)的基因活化，協助植物耐受高溫逆境。為了更進一步了解 HIT4耐 熱的相關機制，本研究 從 hit4突變 植物篩 選出能耐受持續性高溫的逆轉突變株 (hit4 命名為 revertant98 13 (r98 13)。接著 以基因定位的方式， 欲找 尋 使 hit4不耐熱性狀逆轉的突變基因 。研究結果顯示， r98 13突變基因位於阿拉 伯芥第二條色體底部 。此外，為了瞭解參與 HIT4調節染色質中心凝縮或消散的 其他因 子，本研究也從 HIT4 GFP轉植株挑選出染色質中心數目異於野生型植株 的突變株，命名為 18 18 2。 18 18 2具有晚花 及雄配子異常的性狀。另一方面， 本實驗室先前有篩到一棵對持續性熱逆境敏感但耐受熱休克逆性的突變株 hit intolerant 5( 其突變位置坐落於 蛋白質法尼 脂 轉移? (PFT)之 β次單元 基 因上。阿拉伯芥家族 HSP40中的 J2及 J3已經被證實為 PFT的受質蛋白。 J2與 J3的胺基酸序列有高達 90%的相同度 (identity)，但只有 j3剔 除突變株 與 hit5有 相同的熱反應性狀，且與 J3無法被法尼脂化之 轉植株亦同，證實 J3法尼脂化與 否會影響植物對熱逆境的耐受程度。本研究進一步證實法尼脂化對 HSP40與其 他 HSPs間交互作用所產生的影響，及釐清 J2、 J3在熱逆境下分別扮演的角色。;Given that plants are immobile, their growth and development will be hampered seriously if environmental conditions are not suitable for their growth and development. High temperature is one of the abiotic stresses. In order to understand how plants to cope with high temperature stress, we used a forward genetic approach to isolate a heat sensitive mutant of the Arabidopsis named heat intolerant 4 (hit4). The hit4 mutant is sensitive to both prolonged heat stress and sudden heat shock treatment. The role of HIT4 was suggested to bring to date unidentified moleculars away from chromocenter thus allowing heat induced chromocenter decondensation to occur. To understand more about which molecular involved in these heat triggered HIT4 dependent responses, we isolated a revertants of hit4 named revertant 98 13 (r98 13), that restored the ability to tolerate prolonged heat stress like wild type. By map based cloning method, r98 13 mutated locus was shown to locate at a region between AGI map 19,628 kb~19,674 kb of the chromosome II. Meanwhile, we isolated a mutant, named as 18 18 2, whose number of chromocenter is different from that of wild type. The phenotype of 18 18 2 included delayed flowering and abnormal stamen. In addition, we have previously isolated the hit intolerant 5 (hit5) mutant. Incubation at 37°C for 4 days was lethal for hit5 but not for wild type plants. HIT5 encodes the β subunit of protein farnesyl transferase (PFT). Two of the Arabidopsis HSP40 homologs, AtJ2 (J2) and AtJ3 (J3), are PFT substrates. Although J2 and J3 have 90% amino acid sequences identitly, only j3 show the same heat stress phenotypes as hit5. Blocking the farnesylation of J3 in plants also show the same heat stress phenotypes as hit5. These results indicated that J3 involve in the PFT regulated heat stress response. In this study, the roles of J3 in protecting plants against prolong heat stress was also explored.
