Auxin Response Factors and Auxin-Regulated Gene Expression

生长素是一种在调节植物生长发育过程中发挥关键作用的激素，包括器官的形成、侧根的形成、茎和根的伸长、维管组织的形成和分化、顶端优势和向性。许多这些生长素调控的过程可能涉及生长素浓度的局部和短暂变化，导致生长素反应基因的激活或抑制。生长素反应基因的激活被认为触发了下游基因的级联表达，最终导致生长发育的变化。据认为，两种类型的转录因子，即生长素反应因子或ARFs和Aux/IAA蛋白，在调节生长素反应基因表达中相互作用。arf是转录激活因子或抑制因子，已被证明在体外与生长素反应基因启动子中的生长素反应元件（AuxREs）结合。Aux/IAA蛋白是转录抑制因子，不直接与AuxREs结合，但被认为是通过与位于这些启动子元件上的ARF激活因子二聚化而被招募到AuxREs。当细胞中的生长素浓度较低时，ARF激活因子和Aux/IAA抑制因子之间的二聚化被认为会发生，从而导致生长素反应基因的抑制。在生长素浓度升高时，Aux/IAA抑制因子变得不稳定，导致它们从细胞中耗竭，随后生长素反应基因的抑制或激活。相当多的间接证据支持ARF激活因子与Aux/IAA抑制因子相互作用以调节生长素反应基因；然而，缺乏直接证据支持体内arf靶向生长素和Aux/IAA蛋白募集到生长素响应启动子。此外，虽然有大量证据表明生长素调节体内Aux/IAA抑制因子的丰度，但如何调节ARF激活因子的水平以及特定ARF的水平是否决定它们是否以及何时调节特定的生长素反应基因仍有待确定。本研究的重点是为支持或反对ARF和Aux/IAA对生长素反应基因启动子的相互作用提供直接证据。此外，本研究旨在确定哪些ARF蛋白在生长素反应基因中与AuxREs结合，以及ARF蛋白水平如何影响生长素反应基因的表达。建议活动的更广泛影响。这些实验将为本科生、研究生和博士后提供培训。强调本科生的参与[即，MO本科生的荣誉论文和MO和其他本科生通过MO生命科学本科生研究机会计划的暑期实验室体验]。了解ARF和Aux/IAA蛋白如何发挥机制作用，为调节生长素反应基因提供了新的策略，这些基因绕过生长素信号传导并导致表型变化（例如，侧根形成增加）。了解生长素在基因表达水平上的作用机制，以及对ARF和Aux/IAA蛋白的操纵，可能会在农业、农林和园艺领域带来益处。

Auxin is a hormone that plays key roles in regulating a wide range of plant growth and developmental processes, including organ patterning, lateral root initiation, stem and root elongation, vascular tissue formation and differentiation, apical dominance, and tropisms. Many of these auxin-regulated processes likely involve localized and transient changes in auxin concentration that result in activation or repression of auxin response genes. Activation of auxin response genes is thought to trigger a cascade of downstream gene expression, ultimately leading to changes in growth and development. It is thought that two types of transcription factors, referred to as Auxin Response Factors or ARFs and Aux/IAA proteins, interact in regulating auxin response gene expression. ARFs are transcriptional activators or repressors that have been shown to bind in vitro to Auxin Response Elements [AuxREs] in promoters of auxin response genes. Aux/IAA proteins are transcriptional repressors that do not bind directly to AuxREs, but are thought to be recruited to AuxREs by dimerizing with ARF activators that reside on these promoter elements. Dimerization between ARF activators and Aux/IAA repressors is thought to occur when auxin concentrations in a cell are low, resulting in repression of auxin response genes. At elevated auxin concentrations, Aux/IAA repressors become less stable, resulting in their depletion from the cell and subsequent derepression or activation of auxin response genes. A considerable amount of indirect evidence supports ARF activators interacting with Aux/IAA repressors to regulate auxin response genes; however, direct evidence that supports the targeting of ARFs to AuxREs in vivo and the recruitment of Aux/IAA proteins to auxin responsive promoters is lacking. Furthermore, while there is a considerable amount of evidence that auxin regulates the abundance of Aux/IAA repressors in vivo, it remains to be determined how the levels of ARF activators are regulated and if levels of specific ARFs determine if and when they regulate specific auxin response genes. The proposed research is focused on providing direct evidence for or against ARF and Aux/IAA interactions on promoters of auxin response genes. Furthermore, the research is aimed at determining which ARF proteins bind to AuxREs in the auxin response gene and how ARF protein levels affect the expression of auxin response genes. Broader Impacts of the Proposed Activity. The experiments will provide training for undergraduates, graduate students, and postdoctoral associates. The involvement of undergraduates is emphasized [i.e., honors theses for U MO undergraduates and summer laboratory experiences for both U MO and other undergraduates through the U MO Life Sciences Undergraduate Research Opportunity Program]. Understanding how ARF and Aux/IAA proteins function mechanistically is providing novel strategies to regulate auxin response genes that bypass auxin signaling and result in phenotypic changes (e.g., increased lateral root formation). A mechanistic understanding of auxin action at the gene expression level and the manipulation of ARF and Aux/IAA proteins is likely to lead to benefits in agriculture, agriforestry, and horticulture.