FIN219/JAR1藉由酪蛋白激酶2之磷酸化調控遠紅光及茉莉酸訊息溝通路徑

Abstract

植物會持續偵測生長的環境並隨之改變他們的生理代謝、生長及發育，因此外界不同波長的光及植物體內各式荷爾蒙，對於決定植物個體的型態都扮演著很重要的因素。在幼苗發育時期，已知FAR-RED INSENSITIVE 219 (FIN219) 會參與在光敏素A及茉莉酸訊息傳遞路徑中，影響植物光型態形成及茉莉酸反應。但是FIN219蛋白質之轉譯後修飾及其調控機制仍未研究釐清。透由電腦軟體預測顯示FIN219有酪蛋白激酶 (Casein Kinase 2) 之磷酸化位點，並利用試管內磷酸激酶分析試驗證實酪蛋白激酶可磷酸化FIN219，其位點為蘇氨酸 (threonine) 55及69。此外，未磷酸化之FIN219在合成茉莉酯-L-異亮胺酸 (Jasmonyl-L-isoluecine) 之反應擁有較低的解離常數Kd值，代表其對受質有較高的結合性；此外，去磷酸化後之FIN219其穩定性則較差易被分解。我們也發現FIN219在植物體內存在兩種型式，且質量低的型式會因酪蛋白激酶抑制劑4,5,6,7-Tetrabromobenzotriazole (TBB)處理後增加，而且其兩種型式之比例會被遠紅光處理所調節改變。外表型檢測顯示fin219-2對於TBB抑制下胚軸及根長之現象皆較不敏感，並且此抑制下胚生長之現象會被不同強度之遠紅光影響。整合以上，我們提出第一份酪蛋白激酶參與在茉莉酸訊息傳遞路徑中的證據，並且說明FIN219磷酸化狀態之變化參與調節遠紅光及茉莉酸的訊息溝通。

Plants continuously monitor their surrounding environments and change accordingly their physiological metabolism, growth and development. Different spectrums of light and various hormones are essential to determine the shapes and morphologies of individual plants. During the seedling stage, FAR-RED INSENSITIVE 219 (FIN219) has been shown to participate in phytochrome A and Jasmonate signaling pathways, exerting its functions in photomorphogenesis and JA responses. However, the effects of the posttranslational modifications and related regulatory mechanisms on FIN219 protein levels remain to be elucidated. In silico study shows that FIN219 is predicted to contain casein kinase 2 (CK2) phosphorylation sites, and in vitro kinase assay reveals that FIN219 can be indeed phosphorylated by CK2 on the sites of threonine 55 and threonine 69. Moreover, the unphosphorylated form of FIN219 exhibits lower Kd toward the conjugating process of JA-Isoleucine formation, which means higher affinity to its substrates, and is prone to undergo degradation events. We also observed two FIN219 isoforms in planta whose ratios are modulated by 4,5,6,7-Tetrabromobenzotriazole (TBB), a CK2 inhibitor, and by FR light treatments. Phenotypic examinations show that fin219-2 is less sensitive to TBB inhibition on both hypocotyl and root elongation, and the TBB inhibition of hypocotyl growth are modulated by different intensities of far-red light. Taken together, our study provides the first evidence that CK2-mediated phosphorylation of FIN219 participates in JA signaling during seedling development, and is further involved in the cross talk between JA and FR light signaling pathways.