阿拉伯芥GASA4在光及荷爾蒙交互作用中的功能性研究

Abstract

先前利用差異表現法篩選到在綠豆中會受3-5 µm波長紅外光誘導之基因VrGIR1 (gibberellic acid[GA]-and infrared[IR]-induced gene1)，其在阿拉伯芥中的相似基因GASA4 (gibberellic acid-stimulated transcripts in Arabidopsis 4)同樣會受吉貝素及紅外光所誘導，因此本研究致力於了解GASA4在荷爾蒙及紅外光訊息傳遞當中所扮演的角色。吉貝素與茉莉酸分別調控植物的生長發育及防禦，但兩種荷爾蒙之間的交互作用目前還不是很明瞭。GASA4目前已知參與在吉貝素的訊息傳遞路徑中，而FAR-RED INSENSITIVE 219 (FIN219)/JAR1在先前的研究發現會參與在遠紅光及茉莉酸訊息傳遞中。本實驗室先前的研究發現GASA4基因會受FIN219的負調控，因此我們對於兩者在茉莉酸與吉貝素訊息傳遞中所扮演的角色，以及彼此之間的調控關係產生高度興趣。在本次研究當中，我們發現gasa4及fin219突變株都呈現對茉莉酸處理較不敏感的外表型，而對吉貝素處理則較野生型敏感。基因表現的研究則發現FIN219能正調控茉莉酸反應的相關基因表現，如MYC2、VSP1及JAZ1，而GASA4則是扮演負調控者的角色。此外我們也發現GASA4能負調控SPINDLY (SPY)基因表現，而SPY在先前的研究已知能影響DELLA的蛋白質活性。最後我們也發現GASA4能負調控吉貝素訊息傳遞中的負調控者DELLA RGA-LIKE3 (RGL3)的表現，而FIN219則正調控RGL3的表現，RGL3已知也會參與茉莉酸訊息傳遞。綜合以上研究結果，我們推測FIN219與GASA4能藉由調控RGL3表現而共同影響植物中茉莉酸及吉貝素訊息傳遞的進行。除了對荷爾蒙的調控外，本研究也發現GASA4會與PSAK及NPQ4共同參與在紅外光抑制下胚軸的訊息傳遞路徑中，GASA4扮演正調控者的角色，而PSAK及NPQ4則為負調控者。已知二氧化碳能吸收4.3 μm紅外光，推測紅外光能藉由促進植物的固碳作用進而影響光合作用效率，本研究發現紅外光照射能增加C4植物PEP carboxylase基因的表現，並且能延緩玉米與阿拉伯芥葉圓體的老化。綜合以上實驗數據，我們認為GASA4能作為連結光與多種荷爾蒙訊息傳遞的重要因子，並且未來能應用於提高作物產量。

In previous study, gibberellic acid[GA]-and IR-induced gene1 (VrGIR1) was isolated by differential display from mungbean (Vigina radiate) seedlings irradiated with 3~5 µm IR light. Its homolog in Arabidopsis, GASA4 (gibberellic acid-stimulated transcripts in Arabidopsis) was also induced by GA and IR. My thesis aims to investigate the functions of GASA4 in the crosstalk between GA and IR signaling pathways. Jasmonates (JA) and GA are important plant hormones that mainly mediate defense and growth, respectively. However, direct crosstalk between these two hormone pathways remains largely unknown. GASA4 has been shown to participate in GA signaling, and FAR-RED INSENSITIVE 219 (FIN219)/JAR1 was previously shown to play vital roles in far-red (FR) light and JA signaling pathway. Previous study indicated that GASA4 was down-regulated by FIN219. It is interesting to understand the relationship between FIN219 and GASA4 in the integration of both GA and JA signaling. Here, we analyze the regulation between FIN219 and GASA4 in both GA and JA treatments. The results revealed that gasa4 and fin219 mutant showed an insensitive phenotype to JA treatment, but more sensitive to GA treatment. The gene expression studies indicated that FIN219 positively regulated JA responsive genes, but GASA4 negatively regulated them. GASA4 was also found to regulate a GA responsive gene, SPINDLY (SPY), which can alter DELLA protein activity. Moreover, GASA4 negatively regulated DELLA RGA-LIKE3 (RGL3) expression, one of negative regulator of GA signaling that has been shown to participate in JA signaling, whereas FIN219 positively regulates RGL3 expression. Taken together, our data indicate that FIN219 and GASA4 participate in GA and JA signaling via regulating RGL3 expression. In addition to the regulation of GA and JA signaling, GASA4 was also involved in IR signaling pathway. The IR-induced PSAK and NPQ4 genes were acting in this pathway and regulated by GASA4. CO2 can absorb IR wavelength at about 4.3 µm. IR might affect photosynthetic efficiency by improving CO2 fixation. Our studies revealed that IR promotes the expression of PEP carboxylase gene and delays senescence in leaf discs of maize and Arabidopsis. Taken together, our data indicate that GASA4 functions as a crosstalk between light, including IR, and multiple hormones such as GA and JA, and may serve as a good candidate for future applications in improving crop yields.