鋅元素對水稻生理及分子機制調控之研究

Abstract

膳食中的鋅攝取不足已經成為在全世界廣泛發生的問題。瞭解植物尤其是水稻如何調控鋅元素的吸收運輸將有助於我們提高作物中的鋅含量。阿拉伯芥轉錄因子bZIPs (the basic Leucine Zipper Proteins)，AtbZIP19及AtbZIP23透過與 AtZIP4 基因啟動子區域 的Zinc Deficiency Response Element (ZDRE) 之結合，來調控 AtZIP4 轉運子基因的表達，進而調控阿拉伯芥鋅的吸收和運輸；然而，其水稻同源基因(F-OsbZIPs：OsbZIP07, 44, 53) 對鋅元素調控機制目前仍不清楚。為瞭解F-OsbZIPs是否參與水稻鋅之調控機制，本研究以水稻(Oryza sativa L. cv. kitaake) 為材料，以水耕試驗進行不同鋅濃度的處理 (0.002, 0.2, 300 µM)，並分析生理性狀以及基因表現。實驗結果顯示處理後第21天，不論是缺鋅(0.002μM)或過量鋅(300μM)處理，其株高、根長、葉綠素含量、鮮重、乾重等相關生理數值均顯著低於對照組(0.2μM)。基因表現分析結果發現水稻F-OsbZIPs基因幾乎不受鋅處理改變其表現，而具ZDRE基因(OsZIP5, OsZIP7, OsZIP9 )在處理後第三天開始受缺鋅誘導表現，過量鋅則會抑制其表現。而為了對水稻在不同鋅處理下的轉錄體變化有全面的了解，我們同時也進行RNA sequencing (RNA-seq)，發現在216個具ZDRE基因之中，共有20個為差異性表現基因，且表現出受缺鋅誘導及過量鋅抑制的表現模式，結果暗示這些具ZDRE基因可能參與水稻的鋅調控之機制。綜上所述，水稻的F-OsbZIPs轉錄因子可能具有與AtbZIP19、AtbZIP23相似的鋅調控機制，這項發現對於瞭解水稻調控鋅元素吸收運輸的機制以及未來進行水稻的鋅生物營養強化十分重要。

Insufficient Zinc (Zn) intake in the diet has become a series problem, especially for children. To increase the concentration of Zn in crops e.g. rice, it is necessary to understand the Zn‐homeostatic mechanisms in plants. It is still not clear how bZIP transcription factors (F-OsbZIPs: OsbZIP07, 44, 53) are involve in the regulatory mechanism of Zn in rice. To verify the role of F-OsbZIPs and their downstream genes in Zn homeostsis in rice (Oryza Sativa L. Kitaake), this study compared the differential physiologicl and molecular responses undedr different Zn concentration (0.002, 0.2, 300μM). The physiologicl results showed that plant height, root length, fresh weight and dry weight, chlorophyll contents in Zn deficient (0.002) and excess Zn (300μM) treatments were significantly lower than in the control condition (0.2 μM). The molecular analysis indicated that F-OsbZIPs were expressed constitutively while their downstream candidate genes, twenty ZDRE-containing genes (inclusive of OsZIP5, OsZIP7, OsZIP9), are induced under zinc deficiency, but repressed by excess Zn. Overall speaking, our findings imply that the rice F-OsbZIPs exist a similar Zn regulatory mechanism to Arabidopsis AtbZIP transcription factors AtbZIP19 and AtbZIP23. This finding is important to understand the mechanisms of Zn uptake and transport for future biofortification pupose in rice.