阿拉伯芥 HHP1 基因受葡萄糖誘導與離層酸訊息傳導之關係

Abstract

阿拉伯芥 HHP1 (Heptahelical transmembrane protein) 是一個具有7個穿膜區塊的膜蛋白質，先前研究發現 HHP1 基因會受離層酸 (ABA)、滲透壓逆境及蔗糖誘導表現，其功能可能是 ABA 及滲透壓逆境訊息傳導的負向調控子。目前研究指出，葡萄糖的訊息傳導與 ABA 訊息傳導途徑有密切關係。本研究對 pHHP1::GUS 轉殖株進行葡萄糖處理，發現 HHP1 表現量會隨著葡萄糖濃度增加而上升，並且主要表現在未展開的子葉及下胚軸基部，顯示 HHP1 可能與植物對糖反應有關。在 55 及 167 mM 葡萄糖環境中，添加 ABA 會使 HHP1 表現量比以葡萄糖處理時些微增加，顯示葡萄糖和 ABA 共同影響 HHP1 表現可能不是加成作用，兩者可能透過同一訊息傳導路徑調控 HHP1 表現。ABI4 是參與糖及 ABA 訊息傳導之轉錄因子，在對 ABA 與糖不敏感的突變株 abi4-1 中，HHP1 表現量受葡萄糖誘導的程度明顯比 WT 低，表示 HHP1 受糖誘導的過程中可能需要 ABI4參與。綜合本研究之結果，HHP1 受葡萄糖誘導的機制可能與 ABI4 調控的 ABA 訊息傳導路徑有關，且 HHP1 可能作用於 ABI4 下游，並參與植物對糖的反應。

HHP1 (heptahelical protein 1) is a membrane protein with 7 transmembrane domains structure. Previous study has shown that HHP1 is induced by abscisic acid (ABA), osmotic stress and sucrose. Furthermore, HHP1 might act as a negative regulator in ABA and osmotic stress signaling. It is known that ABA signaling components are also involved in glucose signaling. As revealed by histochemical and quantitative analyses of GUS activity of pHHP1::GUS transgenic plants, the expression of HHP1 was increased with glucose concentration, and predominantly shown in the unexpanded cotyledon and the base of hypocotyl, indicating that HHP1 might participate in the response to glucose. Under 55 and 167 mM glucose condition, the glucose-induced HHP1 expression was slightly increased in the presence of ABA. Therefore, glucose and ABA might not act synergistically on the induction of HHP1 expression, suggesting they might act in the same signaling pathway to regulate HHP1 expression. ABI4 (ABA insensitive 4) is a transcription factor which participate in ABA and sugar signaling. In the abi4-1 mutant, which is insensitive to ABA and glucose, the glucose-induced HHP1 expression was significantly reduced than in WT. This result indicated that ABI4 was required for glucose-induced HHP1 expression. Taken together, these data suggested that HHP1 might act downstream of ABI4 and be regulated by ABA-mediated glucose response.