Rapid Divergence of Prolamin Gene Promoters of Maize After Gene Amplification and Dispersal
Rapid Divergence of Prolamin Gene Promoters of Maize After Gene Amplification and Dispersal
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DOI：
10.1534/genetics.112.142372
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发表时间：
2012-10-01
期刊：
影响因子：
3.3
通讯作者：
Messing, Joachim
中科院分区：
文献类型：
--
作者：
Wu, Yongrui;Messing, Joachim
种子已经进化到能够适应复杂的过程，如衰老、休眠和发芽。其中最重要的是储存由光合作用合成的糖和氨基酸衍生的碳水化合物和蛋白质。在禾本科植物中，大部分氨基酸储存在prolamin超家族中，该家族在种子胚乳衰老期间特异性地积累。它们的启动子包含一个保守的顺式元件，称为prolamin-box (P-box)，由反式激活子P-box结合因子（PBF）识别。由于在所有禾本科植物中都缺乏零突变体，其在贮藏蛋白基因表达中的生理作用一直难以捉摸。相比之下，另一种胚乳特异性反式激活子Opaque2 （O2）的零突变体已被证明是通过与O2盒子结合来激活该超家族亚群的转录所必需的。在这里，我们使用RNAi敲低Pbf的表达，发现只有27-kDa γ -和22-kDa α -玉米蛋白基因表达受到影响，而其他玉米蛋白水平保持不变。然而，转基因种子具有不透明的种子表型。PbfRNAi和o2联合作用可进一步降低a-玉米蛋白的表达。我们还测试了启动子的相互作用，并组成性地表达PBF和O2。而转基因启动子可以被激活，内源性启动子似乎无法被转录激活，可能是由于不同的染色质状态。虽然PBF和O2结合位点的甲基化与内源性22-kDa α -玉米蛋白启动子的表达相关，但27-kDa γ -玉米蛋白启动子似乎有不同的机制，它没有发生甲基化变化。
Seeds have evolved to accommodate complicated processes like senescence, dormancy, and germination. Central to these is the storage of carbohydrates and proteins derived from sugars and amino acids synthesized during photosynthesis. In the grasses, the bulk of amino acids is stored in the prolamin superfamily that specifically accumulates in seed endosperm during senescence. Their promoters contain a conserved cis-element, called prolamin-box (P-box), recognized by the trans-activator P-box binding factor (PBF). Because of the lack of null mutants in all grass species, its physiological role in storage-protein gene expression has been elusive. In contrast, a null mutant of another endosperm-specific trans-activator Opaque2 (O2) has been shown to be required for the transcriptional activation of subsets of this superfamily by binding to the O2 box. Here, we used RNAi to knockdown Pbf expression and found that only 27-kDa gamma- and 22-kDa alpha-zein gene expression were affected, whereas the level of other zeins remained unchanged. Still, transgenic seeds had an opaque seed phenotype. Combination of PbfRNAi and o2 resulted in further reduction of a-zein expression. We also tested the interaction of promoters and constitutively expressed PBF and O2. Whereas transgenic promoters could be activated, endogenous promoters appeared to be not accessible to transcriptional activation, presumably due to differential chromatin states. Although analysis of the methylation of binding sites of PBF and O2 correlated with the expression of endogenous 22-kDa alpha-zein promoters, a different mechanism seems to apply to the 27-kDa gamma-zein promoter, which does not undergo methylation changes.