科學家的一項最新研究確定了植物免疫響應過程中的一個關鍵信號——水楊酸甲酯（methyl salicylate）,，這種類似阿司匹林的物質(zhì)能夠提升植物免疫系統(tǒng)的“警戒等級”。該研究成果有望使科學家改造植物的防御能力,，相關論文發(fā)表在10月5日的《科學》雜志上,。
盡管植物并沒有人類的T細胞或者其他免疫功能細胞,，但早在100多年前,，科學家就知道植物也會通過某種信號途徑來引發(fā)整個植物體的免疫抵抗,。這種作用被稱為系統(tǒng)獲得抗病性（systemic acquired resistance），植物被入侵部分發(fā)出的信號會傳播到其他未被感染的部分,。
論文高級作者,、美國康奈爾大學植物研究所的Daniel F. Klessig表示，利用新的發(fā)現(xiàn),，科學家可以通過基因技術改變該信號途徑,，從而提升植物的自身防御能力，提高作物產(chǎn)量,，并減少殺蟲劑的使用,。
1990年，Klessig的小組報告說,，水楊酸和一氧化氮是植物中兩種關鍵的防御信號路徑,。2003年和2005年，該小組在《美國國家科學院院刊》上發(fā)表文章稱,，一種名為SABP2的蛋白酶是植物系統(tǒng)獲得抗病性所必需的,，它能夠使水楊酸甲酯轉(zhuǎn)化成水楊酸。
在這些研究中,，Klessig等人發(fā)現(xiàn),，植物受到病原體攻擊后,，它們在感染部位制造出水楊酸來激活防御機制。其中一些水楊酸會轉(zhuǎn)化成水楊酸甲酯,，后者通過SABP2蛋白重新形成水楊酸,。此外，研究還表明,，在未被感染的植物葉子中,，SABP2必須十分活躍，才能導致系統(tǒng)獲得抗病性完全形成,。與之相比,，在被感染的葉子中，SABP2必須通過與水楊酸結(jié)合,，從而使活性受到抑制,。
“正是這種滅活作用產(chǎn)生了水楊酸甲酯”，Klessig說,，“它通過導管到達未感染組織,，通過SABP2重新形成水楊酸，打開該部位的防御機制,。”
盡管這項新的研究意義重大,，但科學家仍對一個問題迷惑不解，那就是為何植物要如此麻煩地將水楊酸甲酯傳輸?shù)轿锤腥镜慕M織,，而不直接傳輸水楊酸,。（科學網(wǎng) 任霄鵬/編譯）
原始出處:
Science 5 October 2007:
Vol. 318. no. 5847, pp. 113 - 116
DOI: 10.1126/science.1147113
Methyl Salicylate Is a Critical Mobile Signal for Plant Systemic Acquired Resistance
Sang-Wook Park, Evans Kaimoyo, Dhirendra Kumar,* Stephen Mosher, Daniel F. Klessig
In plants, the mobile signal for systemic acquired resistance (SAR), an organism-wide state of enhanced defense to subsequent infections, has been elusive. By stimulating immune responses in mosaic tobacco plants created by grafting different genetic backgrounds, we showed that the methyl salicylate (MeSA) esterase activity of salicylic acid–binding protein 2 (SABP2), which converts MeSA into salicylic acid (SA), is required for SAR signal perception in systemic tissue, the tissue that does not receive the primary (initial) infection. Moreover, in plants expressing mutant SABP2 with unregulated MeSA esterase activity in SAR signal–generating, primary infected leaves, SAR was compromised and the associated increase in MeSA levels was suppressed in primary infected leaves, their phloem exudates, and systemic leaves. SAR was also blocked when SA methyl transferase (which converts SA to MeSA) was silenced in primary infected leaves, and MeSA treatment of lower leaves induced SAR in upper untreated leaves. Therefore, we conclude that MeSA is a SAR signal in tobacco.
Boyce Thompson Institute for Plant Research, Tower Road, Ithaca, NY 14853, USA.
* Present address: Department of Biological Sciences, East Tennessee State University, Johnson City, TN 37614, USA.
Present address: Department of Cell and Systems Biology, University of Toronto, Toronto, Ontario M5S 3B2, Canada.
To whom correspondence should be addressed. E-mail: [email protected]
