The isochorismate pathway is negatively regulated by salicylic acid signaling in O3-exposed Arabidopsis
The isochorismate pathway is negatively regulated by salicylic acid signaling in O3-exposed Arabidopsis
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DOI：
10.1007/s00425-007-0556-5
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发表时间：
2007-10-01
期刊：
影响因子：
4.3
通讯作者：
Saji, Hikaru
中科院分区：
文献类型：
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作者：
Ogawa, Daisuke;Nakajima, Nobuyoshi;Saji, Hikaru
臭氧（O-3）是一种主要的光化学氧化剂，可引起植物叶片损伤。植物合成水杨酸（salicylic acid， SA），据报道对O-3的敏感性有很大影响。然而，O-3暴露下SA生物合成的机制尚不清楚。植物合成SA的途径包括以苯丙氨酸为底物的途径或以等氯酸盐为底物的途径。为了阐明o -3暴露的拟南芥是如何产生SA的，我们检测了苯丙氨酸解氨酶（PAL）和异choris酸合成酶（ICS）的活性，它们分别是苯丙氨酸和等choris酸途径的组成部分。拟南芥暴露于O-3后，SA积累增加，ICS活性增加，PAL活性不受影响。在具有ICS1缺陷的sid2突变体中，SA水平和ICS活性不随O-3暴露而增加。这些结果表明，SA主要是由拟南芥中的等氯酸盐合成的。此外，在缺乏SA信号的植物（npr1和eds5突变体以及NahG转基因）中，暴露于O-3时ICS1的表达水平和ICS的活性升高。SA处理也抑制了O-3对ICS1表达的增强。这些结果表明SA的合成受SA信号的负调控。
Ozone (O-3), a major photochemical oxidant, causes leaf injury in plants. Plants synthesize salicylic acid (SA), which is reported to greatly affect O-3 sensitivity. However, the mechanism of SA biosynthesis under O-3 exposure remains unclear. Plants synthesize SA either by a pathway involving phenylalanine as a substrate or another involving isochorismate. To clarify how SA is produced in O-3-exposed Arabidopsis, we examined the activities of phenylalanine ammonia lyase (PAL) and isochorismate synthase (ICS), which are components of the phenylalanine and isochorismate pathways, respectively. Exposure of Arabidopsis to O-3 enhanced the accumulation of SA and the increase of ICS activity but did not affect PAL activity. In sid2 mutants, which have a defect in ICS1, the level of SA and the activity of ICS did not increase in response to O-3 exposure. These results suggest that SA is mainly synthesized from isochorismate in Arabidopsis. Furthermore, the level of ICS1 expression and the activity of ICS during O-3 exposure elevated in plants deficient for SA signaling (npr1 and eds5 mutants and NahG transgenics). Treatment of plants with SA also suppressed the enhancement of ICS1 expression by O-3. These results suggest that SA synthesis is negatively regulated by SA signaling.