Regulation and antiviral mechanism of a plant ribosome inactivating protein

植物已经进化出几种策略来逃避病原体的攻击和随后的疾病。 核糖体失活蛋白通常被认为与防御有关。 这些酶是由许多植物合成的，从核糖体RNA的保守区域去除嘌呤碱基。 早期的研究表明，这种脱嘌呤作用是如何减慢蛋白质翻译的速度的，由此产生的毒性被用来解释防御作用;也就是说，局部宿主细胞死亡将限制病原体的传播。 然而，很少有人注意到他们的作用机制，在其本土植物。 有趣的是，这些核糖体失活蛋白中的一种首先被发现是因为它的抗病毒特性，而不是毒性。 也就是说，美洲商陆抗病毒蛋白（PAP），由美洲商陆植物合成，抑制几种植物和动物病毒的复制。 我们是第一个证明这种活性是由于病毒基因组RNA的体内脱嘌呤作用;因此，这种酶的底物不限于核糖体RNA。 我们的研究计划的目标将建立在这一重要的发现，以确定PAP是抗病毒的分子机制，在其原生美洲商陆，当在其他异源植物中表达。 我们的短期研究目标有两个方面：1）确定PAP如何靶向病毒RNA而不引起宿主细胞死亡。 我们将在细胞中共定位PAP和病毒RNA，并鉴定可能介导PAP活性的蛋白质。 2)此外，我们想确定如何PAP的表达是在美洲商陆调节，了解其在其原生系统中的作用。 我们将研究PAP表达的转录和转录后控制，通过表征其启动子和PAP特异性小RNA和假基因的功能，我们最近发现。 总之，这些研究的结果将提供有用的信息，以改善作物对病毒的耐受性的策略，并将有助于我们的研究计划的长期目标，以扩大植物的自然防御策略的知识。

Plants have evolved several strategies to evade pathogen attack and subsequent disease. One group of proteins generally thought to be involved in defense is the ribosome inactivating proteins. These are enzymes synthesized by many plants that remove a purine base from a conserved region of ribosomal RNA. Early studies showed how this depurination slowed the rate of protein translation, and resulting toxicity was cited to explain a role in defense; that is, localized host cell death would limit pathogen spread. However, little attention has been paid to their mechanisms of action in their native plants. Interestingly, one of these ribosome inactivating proteins was first discovered because of its antiviral, rather than toxic, properties. Namely, pokeweed antiviral protein (PAP), synthesized by the pokeweed plant Phytolacca americana, inhibits the replication of several plant and animal viruses. We were the first to demonstrate that this activity is due to in vivo depurination of the viral genomic RNA; therefore, the enzyme's substrate is not limited to ribosomal RNA. The objectives of our research program will build on this important finding, to determine the molecular mechanisms by which PAP is antiviral in its native pokeweed and when expressed in other, heterologous plants. Our short-term research objectives are two-fold: 1) to determine how PAP targets viral RNAs without causing host cell death. We will co-localize PAP and viral RNAs in cells and identify proteins that may mediate PAP activity. 2) In addition, we want to determine how PAP expression is regulated in pokeweed, to understand its role in its native system. We will investigate the transcriptional and post-transcriptional control of PAP expression by characterizing its promoter and the functions of a PAP-specific small RNA and pseudogene that we have recently identified. Together, results from these studies will provide useful information to improve strategies for crop tolerance to viruses, and will contribute to the long term goal of our research program to expand knowledge of the natural defense strategies of plants.