阿拉伯芥FIN219與FIP1交互作用在遠紅光與茉莉酸訊息傳遞途徑之功能

Abstract

先前研究顯示Far-red insensitive 219 （FIN219）在阿拉伯芥中扮演兩個角色，分別是遠紅光（FR）訊息傳遞下的正向調控者以及將茉莉酸（Jasmonic acid, JA）接上異亮胺酸（Isoleucine, Ile）以形成具生理活性的JA-Ile之酵素。FIN219-interacting protein 1（FIP1）是會和FIN219產生交互作用的蛋白質之一，研究指出，在活體外的情況下，FIP1可以促進FIN219生成JA-Ile的酵素活性。FIP1屬於穀胱甘肽轉移酶（Glutathione S-transferase tau class, GSTU）家族的一員，受質親和力分析的結果指出，GSTU普遍具有和茉莉酸生合成中間物結合的活性。此外，許多研究發現，當對阿拉伯芥施以JA或其前驅物處理時，可以偵測到一些GSTU的誘導表現，FIP1正是其中之一。我們以這些研究作為依據，想了解在植物體中FIP1是否參與在茉莉酸的訊息傳遞之中。同時，作為雙訊息傳遞路徑的共同調控者，FIN219是如何調控FIP1的表現，以及兩者的交互作用在FR或JA訊息傳遞下扮演的角色仍有待釐清。本研究中，我們使用了基因轉殖與雜交技術來探討上述的問題。根據實驗結果，我們發現FIP1的表現的確會被短時間或低濃度的JA處理所誘導，而在這樣的情況下，若將FIP1的mRNA量以外加的互補股抑制 (fip1as)，植物的根部生長對JA的反應則會顯著降低，同時與JA相關的基因表現也會隨之降低。此外，在大量表現FIP1的轉殖株當中，會有對JA更為不敏感的外表型和受抑制的JA相關基因表現，這些結果顯示FIP1的存在對於JA的訊息傳遞有一定的重要性。我們還發現FIN219的表現也會受到FIP1的調控，而在FIP1FIN219和FIP1的雙突變株顯示了更明顯的JA訊息傳遞缺陷，表示FIP1和FIN219之間具有一定的關聯。透過與報導基因的結合，我們發現FIP1無論在細胞中或組織間，其分布位置都呈現專一性，這些特殊的表現位置不但與JA生合成和調控區域具有高度相關性，還會受到JA處理的影響，更加暗示了FIP1和茉莉酸訊息傳遞間的關聯性。

Previous studies showed that FIN219 is not only a positive regulator in far-red (FR) light signaling but a jasmonic acid (JA) conjugating enzyme. The conjugation of JA with isoleucine (Ile) by FIN219 leads to the bio-active JA-Ile that triggers the downstream JA signaling. FIN219-interacting protein 1 (FIP1) was found to interact with FIN219 under in vitro and in vivo conditions. Further investigation found that this interaction can enhance the enzyme activity of FIN219. Besides, FIP1 is a tau class member of the glutathione S-transferase (GSTU) superfamily in Arabidopsis. Previous research indicated that GSTU members are able to bind with oxylipins and some of them, including FIP1, could be induced by JA rapidly. Given that JA belongs to oxylins, the interaction of FIP1 and FIN219 may positively regulate JA signaling in Arabidopsis. In this study, we used transgenic plants that had changes of FIN219 and FIP1 expression levels; reporter gene fusion proteins were also harbored to verify the physical functions of FIP1 and FIN219. Here, we found that FIP1 was induced by JA rapidly as well as by low concentrations of JA persistently. Furthermore, the knocked-down of FIP1 under these conditions led to a negative effect on JA signaling. Surprisingly, the overexpression of FIP1 leads to various JA sensitivity effects by JA and its derivatives. The JA deficiencies caused by the fip1as/fin219-2 double mutant implies the coordinative functions of these two genes in JA signaling. Finally, the tissue-specific data showed that FIP1 and FIN219 were highly associated with the JA-related function areas. To sum up, these results provide an insight into the GSTU-modulated JA signal pathway.