Ezcurra I, Wycliffe P, Nehlin L, Ellerström M, Rask L
Department of Plant Biology, Swedish University of Agricultural Sciences, Box 7055, S-750 07 Uppsala, Sweden.
Plant J. 2000 Oct;24(1):57-66. doi: 10.1046/j.1365-313x.2000.00857.x.
The transcriptional activator ABI3 is a key regulator of gene expression during embryo maturation in crucifers. In monocots, the related VP1 protein regulates the Em promoter synergistically with abscisic acid (ABA). We identified cis-elements in the Brassica napus napin napA promoter mediating regulation by ABI3 and ABA, by analyzing substitution mutation constructs of napA in transgenic tobacco plantlets ectopically expressing ABI3. In transient analysis using particle bombardment of tobacco leaf sections, a tetramer of the distB ABRE (abscisic acid-responsive element) mediated transactivation by ABI3 and ABI3-dependent response to ABA, whereas a tetramer of the composite RY/G complex, containing RY repeats and a G-box, mediated only ABA-independent transactivation by ABI3. Deletion of the conserved B2 and B3 domains of ABI3 abolished transactivation of napA by ABI3. The two domains of ABI3 interact with different cis-elements: B2 is necessary for ABA-independent and ABA-dependent activations through the distB ABRE, whereas B3 interacts with the RY/G complex. Thus B2 mediates the interaction of ABI3 with the protein complex at the ABRE. The regulation of napA by ABI3 differs from Em regulation by VP1, in that the B3 domain of ABI3 is essential for the ABA-dependent regulation of napA.
转录激活因子ABI3是十字花科植物胚胎成熟过程中基因表达的关键调节因子。在单子叶植物中，相关的VP1蛋白与脱落酸（ABA）协同调节Em启动子。我们通过分析在异位表达ABI3的转基因烟草幼苗中napA的替代突变构建体，鉴定了甘蓝型油菜napin napA启动子中介导ABI3和ABA调控的顺式元件。在使用烟草叶片切片进行粒子轰击的瞬时分析中，distB ABRE（脱落酸应答元件）的四聚体介导了ABI3的反式激活以及ABI3对ABA的依赖性应答，而包含RY重复序列和一个G盒的复合RY/G复合体的四聚体仅介导了ABI3不依赖ABA的反式激活。ABI3保守的B2和B3结构域的缺失消除了ABI3对napA的反式激活。ABI3的这两个结构域与不同的顺式元件相互作用：B2对于通过distB ABRE进行的不依赖ABA和依赖ABA的激活是必需的，而B3与RY/G复合体相互作用。因此，B2介导了ABI3与ABRE处蛋白质复合体的相互作用。ABI3对napA的调控不同于VP1对Em的调控，因为ABI3的B3结构域对于napA依赖ABA的调控至关重要。
