Harris L J, Saparno A, Johnston A, Prisic S, Xu M, Allard S, Kathiresan A, Ouellet T, Peters R J
Eastern Cereal and Oilseed Research Centre, Agriculture and Agri-Food Canada, Building #21, Central Experimental Farm, K1A 0C6, Ottawa, Ont, Canada.
Plant Mol Biol. 2005 Dec;59(6):881-94. doi: 10.1007/s11103-005-1674-8.
Using the technique of differential display, a maize transcript was identified whose silk tissue expression is induced in the presence of the ear rot pathogen Fusarium graminearum. The 3445 nt transcript includes a 727 nt 5' untranslated leader with the potential for extensive secondary structure and represents the maize gene An2. An2 encodes a copalyl diphosphate synthase (CPS)-like protein with 60% amino acid sequence identity with the maize An1 gene product involved in gibberellin (GA) biosynthesis. Recombinant expression and functional analysis demonstrated that both AN1 and AN2 are ent-copalyl diphosphate (ent-CPP) synthases (ent-CPS). Notably, the presence of an additional ent-CPS gene is consistent with previous reports that maize GA biosynthesis can proceed in the absence of An1. In addition, northern blot analysis showed that An2 transcript levels were strongly up-regulated by Fusarium attack, with an increase in silk, husk and ear tip tissues as early as 6 h after inoculation of silk channels with spore suspensions of various Fusarium sp. Gene expression of a third maize CPS-like gene, Cpsl1, is not affected by Fusarium infection. The Fusarium-inducible nature of An2 is also consistent with a previous report that cell-free extracts from maize seedlings produce ent-CPP derived diterpenes in response to Fusarium infection. However, it is not known whether An2 is involved in defense-related secondary metabolism in addition to GA synthesis.
利用差异显示技术，鉴定出一种玉米转录本，其在存在穗腐病原菌禾谷镰刀菌的情况下，花丝组织表达被诱导。该3445 nt转录本包含一个727 nt的5'非翻译前导序列，具有形成广泛二级结构的潜力，代表玉米基因An2。An2编码一种柯巴基二磷酸合酶（CPS）样蛋白，与参与赤霉素（GA）生物合成的玉米An1基因产物具有60%的氨基酸序列同一性。重组表达和功能分析表明，AN1和AN2都是内根-柯巴基二磷酸（ent-CPP）合酶（ent-CPS）。值得注意的是，额外存在一个ent-CPS基因与之前关于玉米GA生物合成可以在没有An1的情况下进行的报道一致。此外，Northern印迹分析表明，An2转录本水平在镰刀菌攻击下强烈上调，早在用各种镰刀菌的孢子悬浮液接种花丝通道后6小时，花丝、苞叶和穗尖组织中的An2转录本水平就有所增加。第三个玉米CPS样基因Cpsl1的基因表达不受镰刀菌感染的影响。An2的镰刀菌诱导特性也与之前的一份报告一致，该报告称玉米幼苗的无细胞提取物在受到镰刀菌感染时会产生源自ent-CPP的二萜类化合物。然而，尚不清楚An2除了参与GA合成外是否还参与与防御相关的次生代谢。
