永續計畫資料庫

Challenges of water conservation for rice cropping II: develop water-saving rice cultivars             

In Taiwan, rice (Oryza sativa L.) is predominantly grown on soils with prolonged submergence, requiring large quantities of fresh water. To cope with an increasing shortage of water resources, there is an urgent need to research the most water-saving technique and water-use efficient cultivars for rice production. However, on the one hand, using water-saving irrigation systems (i.e., aerobic cultures) alters depth profiles of soil moisture and redox potential (Eh), which may lead to a decrease in available soil water and nutrients, thereby causing yield reduction. Significantly, rich Fe(II) in the soil is oxidized to Fe(III) and becomes less available to rice plants.                

Our preliminary study found some effects of Fe deficiency on delay-flowering of rice resulting in the deduced production. In the previous granting period, an exciting outcome that turned up Fe(II) uptake system by overexpressing a strong Strategy-I transcription factor IDT1A320V in rice resulted in increased Fe uptake and high grain yield, up to almost two times compared to wildtype, under water-saving irrigation conditions, despite such excellent phenotypes were compromised in the T2 generation with gene shutting down. Based on this, we hypothesize that Fe forms, Fe(II) and Fe(III), are critical for rice growth. If sifted to water-saving regimes, domesticated rice plants must overcome the shortage of Fe(II) in the relatively dry soil. On the other hand, after continuous flooding is shifted to water-saving regimes, there is often a trade-off between CH4 and N2O emissions, decreasing CH4 but increasing N2O fluxes. Still, the differences in greenhouse gas (GHGs) emissions associated with planting methods and rice varieties are far from conclusive. Therefore, regarding contributions to the greenhouse effect, GHGs emissions from rice filed should be simultaneously measured. Following the rationale, this project aims to develop transgenic Fe-biofortified (Aim-1) and drought-insensitive (Aim-2) rice plants for water-saving practice.              

Also, the nutrient effects of water-saving irrigation practices and drought-insensitive on GHGs emissions will be evaluated (Aim-3). In Aim-1, we will overexpress IDT1A320V in rice, using rice endogenous and high expression promotors to ensure that the transgene will function in the same manner as T1 in their offspring. Therefore, genetically inherited traits can be characterized. Alternatively, in Aim-2, we will use forward genetic screening with sodium azide (NaN3)-mutated rice to identify mutants showing tolerance/resistance to water deficit. Furthermore, a field experiment will be conducted to monitor CO2, CH4, and N2O emissions and nutrient forms using water-saving irrigation strategies in Aim-3. The results will help provide more information not only for better water conversation than traditional water-abundant ways but mitigate GHG emissions and improve the water-use efficiency of rice with guarantee yield stability.          

在台灣，水稻 (Oryza sativa L.)主要生長在長期淹水的土壤中，需要大量的灌溉水。為應對日益嚴重水資源不平衡的問題，迫切需要研究節水的水稻生產技術和節水耐旱的水稻品種。然而，一方面，使用節水灌溉系統改變了土壤水分和氧化還原電位 (Eh)的分布，這可能會導致植物可利用有效水分以及土壤有效養和的減少，從而導致產量下降。                  

 其中，在通氣土壤中二價鐵會氧化為三價鐵沈澱，進而降低鐵的生物有效性。我們的初步研究指出，缺鐵對水稻延遲開花有一定的影響，而導至產量下降。此外，在108年的永續計畫中，我們發現在節水耕作的條件下，通過過量表現IDT1A320V (為二價鐵吸收的策略 I 之重要轉錄因子)於策略 II 的水稻中，可增加植株對二價鐵的吸收，及令人驚訝地提高其產量幾乎是野生型的兩倍，然而在 T2 代卻失去了這一表型及基因表現。依此，我們假設土壤中鐵的生物有效性在水稻生長過程中扮演至關重要的角色。也就是說，如果使用旱作方式馴化水稻，其必須克服通氣土壤中二價鐵的短缺。                       

另一方面，以節水耕作取代傳統連續淹灌模式，於耕種過程中釋出的溫室氣體往往存在取捨與權衡，即 CH4 減少而N2O 排放增加。儘管如此，不同的種植方法與水稻品種如何影響溫室氣體排放的差異尚未有定論。因此，稻田溫室氣體於不同種植條件下之排放應持續測量，相關數據將有助於減降農作生產排放溫室氣體之對策。                  

基於上述問題，本計畫旨在節水灌溉條件下，通過轉基因方式強化作物鐵營養的吸收以對抗節水耕作(目標-1)以及篩選出耐旱節水水稻新品系 (目標-2)的備案。此外，於目標-3 中，我們將評估以節水灌溉方式種植耐旱節水水稻情況下對溫室氣體排放及土壤養分形式之影響。在目標-1 中，我們將過量表達 IDT1A320V於水稻中，以增加在節水耕作模式下水稻鐵的吸收。            

其中，我們將使用水稻內源性啟動子，以確保該轉基因在其後代中以與T1 相同的方式發揮作用。在目標-2 中，我們將使用疊氮化鈉(NaN3)誘變水稻進行正向遺傳篩選，以識別耐/抗水分脅迫的水稻突變株，及儘可能精準定位相對應的基因。此外，我們將在目標-3 進行田間試驗，以監測利用節水灌溉策略下種植耐旱節水水稻，其溫室氣體 (包括 CO2、CH4 和 N2O) 的釋出及土壤營養形式變化。研究結果將提供更多資訊以利提高台灣種植水稻水資源的利用效率，以及降低水稻種植過程中溫室氣體的排放。