Functional analysis of a rice importin-α binding protein

为了鉴定与植物光环境反应相关的新的核蛋白，作者分析了一个候选蛋白IABP4的功能，该蛋白是通过与核运输机械的组成部分水稻Importin-α1a(IMPα1a)结合而分离出来的，该蛋白在黑暗中表达强，在光下表达下调。主要研究结果如下：1.基因表达及光照效应：与水稻IMPIABP1a基因类似，α基因在水稻和拟南芥黄化苗和绿苗中的表达均受光照的下调。结果表明，IABP4在黑暗中的核积累可能由于IABP4蛋白水平的降低以及IAB P4.2核输入的减少而减少。2.基因敲除系的功能分析：在拟南芥中鉴定到5个IABP4基因敲除系，并且在黑暗中具有开钩和子叶的幼苗比例高于野生型，这表明IABP4蛋白可能抑制了潮湿条件下的光形态建成。由于萌发的幼苗都是T-DNA插入的杂合子，纯合子被认为是胚胎致死的或不能萌发的，这表明IABP4不仅参与了光形态建成的控制，而且对植物来说也是必不可少的。3.大体内定位和光的影响：虽然我们获得了IABP4抗血清，但它含有对其他植物蛋白的抗体，所以我们不能利用它进行定位研究。通过纯化抗体或利用GFP融合，迫切需要对IABP4的核定位进行检测。

To identify novel nuclear proteins that are involved in plants' responses to light environment, the author analyzed the function of a candidate protein, named IABP4, that had been isolated by its binding to rice importin-α1a(IMPα1a), a component of nuclear transport machinery, whose expression is strong in the dark and is down-regulated by light. The obtained results are as follows.1.Gene expression and the effect of light : Similar to rice IMPα1a gene, the expression of IABP4 was down-regulated by light both in etiolated-and green-seedlings of rice and Arabidopsis. The result suggests that nuclear accumulation of IABP4 might be reduced in the dark as a result of reduced IABP4 protein level as well as reduced nuclear import of IAB P4.2.Functional analysis by knockout lines : Five knockout lines of IABP4 were identified in Arabidopsis, and the proportion of seedlings with open hook and cotyledons in the dark was higher in the knockouts than in wild type, suggesting that IABP4 protein may be suppressing photomorphogenesis in the dank. Because germinated seedlings were all hetero-zygous with respect to T-DNA insertion, the homozygote is considered to be embryonic lethal or unable to germinate, suggesting that IABP4 is not only involved in the control of photomorphgenesis but also essential for plants.3.IntraceMar localization and the effect of light: Though we obtained IABP4 antiserum, it contained antibodies to other plant proteins, so we could not use it for localization studies. By purifying antibody or by using GFP-fusion, examination of nuclear localization of IABP4 is urgently required.