大豆galactinol synthase基因在各種逆境下的表現

Abstract

植物遭遇乾燥與低溫等逆境時，會誘導基因表現，產生種種生理與生化變化以適應環境。這些基因產物能避免逆境對植物造成傷害，RFOs（Raffinose Family Oligosaccharides）便是其中之一，其主要代表分子有raffinose與stachyose；因RFOs除在逆境下會累積外，在植物種子發育期間亦會累積，能減輕環境逆境對植物的影響，故被認為參與植物及種子的耐旱性。 Galactinol synthase（GolS），能催化UDP-galactose和myo-inositol生合成galactinol，為RFOs生合成的關鍵酵素。從過去的研究發現豆科植物經低溫處理後其葉子內RFOs會大量生成。本研究目的在探討大豆GolS基因有幾個，是否受不同逆境所誘導。糖類分析顯示大豆植株在缺水的情況下，葉子內會累積galactinol和raffinose，不過並未發現stachyose的累積；至於正常供水的植株則無任何RFOs累積，故可推測galactinol和raffinose參與大豆對乾燥逆境的耐受力。另外也發現在大豆種子發育過程中，RFOs的累積以stachyose為主。本研究從大豆葉子中找出兩個GolS基因（GmGolS 1, GmGolS 2），將大豆植株分別以乾燥、高鹽和低溫等逆境處理，觀察兩個GolS基因的表現；發現在乾燥、低溫和高鹽逆境處理下，GmGolS 2 mRNA在大豆植株各個器官，包含根、莖、葉組織內，其表現量均會受到誘導；而GmGolS 1則只受高鹽逆境誘導，且轉錄物只在大豆植株根部累積。

Gene expression is induced when plant subjected to stresses, like drought and low temperature, and biochemical and physiological responses allow plant to adapt to the environmental stimuli. Raffinose family oligosaccharides (RFOs), for example, stachyose and raffinose, are of the biochemical product induced under stresses. In addition, RFOs also accumulate during seed maturation and participate in the drought tolerance of vegetative part and seeds. Galactinol synthase (GolS) catalyzes the formation of galactinol from the substrates UDP-galactose and myo-inositol. RFOs accumulation was reported previously under low temperature in legume plants. The purpose of this study is to investigate the gene number of expressed GolS and their expression under different environmental stimuli. Sugar analysis of soybean leaf under drought indicates the accumulation of galactinol and raffinose, but not stachyose. These sugars, however, do not accumulate in the control plants. Accumulation of RFOs, especially stachyose, is also found in developing seeds. We have isolated two GolS genes (GmGolS 2 and GmGolS 2) from soybean leaves. GmGolS 2 is induced in root, stem and leaf under drought, low temperature and high salt, whereas GmGolS 1 is induced only in root under high salt.