阿拉伯芥麩胺基硫轉移酶 AtGSTU17 突變株耐旱及耐鹽性狀為麩胺基與離層酸共同作用之結果

Abstract

麩胺基硫轉移酶 (glutathione s-transferases, GSTs) 在氧化逆境代謝中扮演一個相當重要的角色，但對於這類基因在植物體內所扮演的個別功能卻所知有限。在整個GST基因家族中GLUTATHIONE S-TRANSFERASE U17 (AtGSTU17, At1g10370) 曾有被報導其參與了光的傳導訊息調控；經由與phyA的交互作用，影響了植物體內的GSH含量，進一步影響了植物的生長發育。 本篇論文提供進一步的研究證據顯示AtGSTU17在乾旱及鹽分逆境下扮演一個重要的負調控角色。阿拉伯芥的atgstu17突變株比野生型更為耐旱及耐鹽。生理分析顯示atgstu17突變株的植物體累積了較高含量的GSH與ABA，同時在發芽時期對於ABA較不敏感，葉片的氣孔孔徑較小，較低的水分蒸發速率，根系發育更為茂盛以及較長的營養生長期等生理性狀。 為了釐清atgstu17突變株累積的ABA是否是因為GSH含量升高引起，我們對野生型澆灌GSH溶液進行研究。結果發現澆灌GSH溶液的野生型，其ABA含量較未澆灌GSH的植株高，同時顯現atgstu17突變株的生理性狀，如開花延遲，根部發育，較為耐鹽與耐旱等。進一步研究atgstu17突變株是否是因為GSH與ABA累積影響而產生了上述的生理性狀。我們將atgstu17突變株種植在L-buthionine-(S,R)-sulfoximine (BSO)溶液中。BSO是一種可以抑制植物的GSH生合成的專一性藥劑。當atgstu17突變株的GSH含量受到BSO抑制減少到與野生型相同的含量時，觀察其性狀與生理反應，如根系，開花時間與對於鹽分與乾旱的耐受性等，顯示與野生型類似。由以上實驗結果可以得到一個結論，atgstu17突變株的外表性狀是由於其植物體內含有較高的GSH與ABA所共同作用而產生的結果。同時經由DNA微陣列 (microarray) 的資料顯示許多與生長或逆境相關的轉錄調控基因受到AtGSTU17的影響而改變表現。綜合以上實驗資料結果，我們推測AtGSTU17扮演了植物逆境訊息傳導反應的負調控功能。

Although glutathione S-transferases (GSTs) are thought to play major roles in oxidative stress metabolism, little is known about the regulatory functions of GSTs. We have reported that GLUTATHIONE S-TRANSFERASE U17 (AtGSTU17, At1g10370) participates in light signaling and might modulate various aspects of development by affecting glutathione (GSH) pools via a coordinated regulation with phyA. Here we provided further evidence to support a negative role of AtGSTU17 in drought and salt stress tolerance. When AtGSTU17 was mutated, plants were more tolerant to drought and salt stresses compared to wild-type (WT, Col-0) plants. In addition, atgstu17 accumulated higher level of GSH and abscisic acid (ABA), and exhibited hyposensitivity to ABA during seed germination, smaller stomatal apertures, a lower transpiration rate, better development of primary and lateral root systems, and longer vegetative growth. To explore how atgstu17 accumulated higher ABA content, we grew WT in the solution containing GSH and found that plants accumulated ABA to a higher extent than plants grown in the absence of GSH, and exhibited the atgstu17 phenotypes. WT plants treated with GSH also demonstrated more tolerant to drought and salt stresses. Furthermore, the effect of GSH on root patterning and drought tolerance was confirmed by growing the atgstu17 in solution containing L-buthionine-(S,R)- sulfoximine (BSO), a specific inhibitor of GSH biosynthesis. In conclusion, the atgstu17 phenotype can be explained by the combined effect of GSH and ABA. Microarray analysis provided evidence that expressions of many genes related to growth and stress inducible transcription factors altered in the atgstu17 mutants. We propose a role of AtGSTU17 in adaptive responses to drought and salt stresses, by functioning as a negative component of stress-mediated signal transduction pathways.