Garretón Virginia, Carpinelli Jorge, Jordana Xavier, Holuigue Loreto
Departamento de Genética Molecular y Microbiología, Facultad de Ciencias Biológicas, P. Universidad Católica de Chile, Santiago, Chile.
Plant Physiol. 2002 Nov;130(3):1516-26. doi: 10.1104/pp.009886.
The activation sequence-1 (as-1)-like element found in the promoter of some glutathione S-transferase (GST) genes, has been previously described as a salicylic acid (SA)- and auxin-responsive element. In this paper, we tested the hypothesis that the activating effect of SA on the as-1 element is mediated by oxidative species. Supporting this hypothesis, our results show that the antioxidants dimethylthiourea (DMTU) and 3-t-butyl-4-hydroxy-anizole (BHA) inhibit the SA-induced transcription of genes controlled by as-1 elements in tobacco (Nicotiana tabacum) plants [i.e. GNT35 gene coding for a GST and (as-1)(4)/beta-glucuronidase (GUS) reporter transgene]. DMTU and BHA also inhibit SA-activated as-1-binding activity in nuclear extracts. Further support for the hypothesis that the as-1 element is activated by oxidative species comes from our result showing that light potentiates the SA-induced activation of the as-1 element. Furthermore, methyl viologen, a known oxidative stress inducer in plants, also activates the as-1 element. Increasing H(2)O(2) levels by incubation with H(2)O(2) or with the catalase inhibitor 3-amino-1,2,5-triazole does not activate the (as-1)(4)/GUS gene. On the contrary, 3-amino-1,2,5-triazole inhibits the activating effect of SA on the (as-1)(4)/GUS gene. These results suggest that oxidative species other than H(2)O(2) mediate the activation of the as-1 element by SA. Our results also suggest that even though the as-1 binding activity is stimulated by oxidative species, this is not sufficient for the transactivation of genes controlled by this element. The complex interplay between SA and reactive oxygen species in the transcriptional activation of defense genes is discussed.
在一些谷胱甘肽S-转移酶（GST）基因启动子中发现的激活序列-1（as-1）样元件，先前已被描述为水杨酸（SA）和生长素响应元件。在本文中，我们检验了如下假说：SA对as-1元件的激活作用是由氧化物质介导的。支持这一假说的是，我们的结果表明抗氧化剂二甲基硫脲（DMTU）和3-叔丁基-4-羟基茴香醚（BHA）抑制了SA诱导的烟草（Nicotiana tabacum）植株中由as-1元件控制的基因的转录[即编码一种GST的GNT35基因和（as-1）（4）/β-葡萄糖醛酸酶（GUS）报告转基因]。DMTU和BHA还抑制了核提取物中SA激活的as-1结合活性。对as-1元件由氧化物质激活这一假说的进一步支持来自我们的结果，即光照增强了SA诱导的as-1元件的激活。此外，甲基紫精是植物中一种已知的氧化应激诱导剂，它也激活as-1元件。通过与H₂O₂或过氧化氢酶抑制剂3-氨基-1,2,5-三唑孵育来提高H₂O₂水平并不能激活（as-1）（4）/GUS基因。相反，3-氨基-1,2,5-三唑抑制了SA对（as-1）（4）/GUS基因的激活作用。这些结果表明，除H₂O₂之外的氧化物质介导了SA对as-1元件的激活。我们的结果还表明，尽管as-1结合活性受到氧化物质的刺激，但这对于由该元件控制的基因的反式激活并不充分。本文讨论了SA与活性氧在防御基因转录激活中的复杂相互作用。
