非專一性脂質運輸蛋白質 OsLTP2 對水稻生長及離層酸合成之影響

Abstract

植物非專一性脂質運輸蛋白 (non-specific lipid transfer proteins, nsLTPs) 是具有結合與運輸各類疏水性分子功能的鹼性蛋白質，可與脂肪酸、磷脂酸、醣脂質、乙醯輔酶A、類固醇、芳香類化合物及角質單體等多種疏水性分子在體外結合。水稻基因體中有52個脂質運輸蛋白基因，我們過去的研究已知OsLTP2會在Glutathione reductase 2-RNAi及 Ascorbate peroxidase 8突變體幼苗葉片中受鹽逆境大量表達。因此，本研究利用台農67號水稻為試驗材料，分析 OsLTP2 大量表現 (Overexpression, OsLTP2-OE) 與弱化表現 (RNA interference, OsLTP2-RNAi) 轉殖水稻之分子特性與外表性狀調查。結果顯示 OsLTP2-RNAi 轉殖株的株高、鮮重及乾重皆顯著低於野生型水稻與 OsLTP2-OE，分別降低31%、23%及25%。葉鞘切片結果顯示矮化現象是地上部細胞長度減少所導致。降低OsLTP2表現量使水稻產量下降且榖粒發育畸形，榖粒白堊質大量累積降低稻米品質。同時離層酸生合成相關基因9-cis-epoxycarotenoid dioxygenase (OsNCED3、OsNCED4、OsNCED5)、ABA訊號傳遞基因OsABI3、 OsABI4及ABA反應基因OsRab16a也會受誘導，而離層酸代謝基因Rice ABA 8’-hydroxylase (OsABA8ox3) 的表現則受抑制，導致幼苗地上部的離層酸含量顯著增加。這些結果顯示，OsLTP2 可能參與調節水稻生長發育及離層酸的合成。然而，OsLTP2-RNAi轉殖株雖然可提高內生離層酸的含量，但在鹽分逆境下的耐受性與野生型水稻及OsLTP2-OE轉殖株並沒有顯著差異，因此其生理功能有待進一步探討。

Plant non-specific lipid transfer proteins (nsLTPs) are basic proteins, which have the ability to bind or transfer various types of hydrophobic molecules in vitro, such as fatty acids, fatty acyl-CoA, glycolipids, phospholipids and cutin monomers. Rice LTP is a large gene family consisting of 52 nsLTPs genes. Our previous results have revealed that the expression of OsLTP2 was notably increased in glutathione reductase 2-RNAi and ascorbate peroxidase 8 rice mutant as compared to wild-type (WT) under salt stress. In this study, OsLTP2 overexpression (OsLTP2-OE) and RNA interference (OsLTP2-RNAi) transgenic lines were used to study the physiological roles of OsLTP2 in rice. Results showed that knockdowned OsLTP2 mRNA by RNA interference lead to reduction of plant height (31%), fresh weight (23%), dry weight (25%) and yield as compared to WT, whereas no difference was observed between WT and OsLTP2-OE. Reduced expression of OsLTP2 caused a reduced cell size in leaf sheath of seedlings, abnormal grains with high chalkiness. Simultaneously, expression of abscisic acid biosynthetic genes, 9-cis-epoxycarotenoid dioxygenase (OsNCED3, OsNCED4, OsNCED5)、ABA signaling genes including OsABI3 and OsABI4 and ABA responsive gene OsRab16a were induced. However, the ABA catabolic gene, rice ABA 8’-hydroxylase (OsABA8ox3) was suppressed, leading to an increased levels of abscisic acid in shoots of rice seedlings. These results show that OsLTP2 may participate in the regulation of rice growth, development and abscisic acid biosynthesis. Nevertheless, OsLTP2-RNAi showed an increased concentration of abscisic acid in shoots of seedlins, but the tolerance to salt stress was not able to find significant difference as compared to TNG67 and OsLTP2-OE.