Auxin Response Factors and Auxin Regulated Transcription

摘要MCB-0080096 Thomas Guilfoyle和Gretchen HagenGuilfoyle 生长素是一种植物激素，在植物的分化生长、根的形成、顶端优势和维管形成中起重要作用。 这些生长和发育过程可能至少部分地受到初级（或早期）和次级（或晚期）生长素反应基因的表达模式的调控。 早期生长素应答基因包含一个或多个含有TGTCTC序列的生长素应答元件（Auxin Response Elements，AGRE），其赋予生长素对启动子的应答。 生长素反应因子[ARF]是特异性结合TGTCTC受体的转录因子。 ARF含有一个氨基末端DNA结合结构域[DBD]，大多数ARF含有一个保守的羧基末端结构域[CTD]，该结构域有助于ARF自身或Aux/IAA蛋白的二聚化。 位于ARF DBD和CTD之间的氨基酸是非保守的，代表激活或抑制结构域。 特异性ARF可以通过直接结合TGTCTC β RE来激活或抑制生长素响应性转录，并且可以通过与结合于β RE的ARF二聚化来进一步增强转录激活或抑制。 虽然Aux/IAA蛋白不直接与TGTCTC β-受体结合，但它们也可能通过与结合于β-受体的ARF形成异二聚体来加强对β-受体的抑制[或可能的激活]。 主要问题来自于拟南芥中许多ARF和Aux/IAA蛋白的鉴定。 具有相似DNA结合结构域的特异性ARF如何靶向特定TGTCTC靶向受体？ ARF、Aux/IAA和ARF-Aux/IAA蛋白质的特定对的形成是由什么控制的？ ARF和Aux/IAA同源二聚体和异源二聚体如何决定生长素反应基因是被激活还是被抑制？ 生长素是否在将特定ARF靶向TGTCTC靶向REs、选择形成的二聚体类型和/或确定激活或抑制结构域是否存在于TGTCTC靶向REs中发挥作用？ 还有哪些转录和信号因子与ARF和Aux/IAA蛋白一起参与沿着调节初级生长素反应基因？ 长期目标是回答这些问题，并开始解开看似复杂的ARF和Aux/IAA相互作用的网络，必须发生在细胞内调节生长素反应基因的表达。 该项目的具体目标如下： (1)确定ARF和Aux/IAA蛋白是否在相互作用中显示选择性;（2）确定生长素是否直接影响ARF激活或阻遏结构域，或者是否ARF CTD是生长素响应性激活或阻遏所必需的;（3）确定富Q ARF激活剂是否在生长素响应性基因表达中起冗余作用;（4）确定ARF的基因表达模式是否可能限制植物中ARF和Aux/IAA二聚体的类型;（5）鉴定除Aux/IAA外与ARF相互作用并在生长素信号传导和生长素反应中起作用的蛋白质。

AbstractMCB-0080096Thomas Guilfoyle and Gretchen HagenGuilfoyle Auxin is a plant hormone known to play important roles in differential growth, root formation, apical dominance, and vascular patterning. These growth and developmental processes may be regulated, at least in part, by the expression patterns of primary (or early) and secondary (or late) auxin response genes. Early auxin response genes contain one or more Auxin Response Elements [AuxREs] containing the sequence TGTCTC, which confers auxin responsiveness to the promoters. Auxin Response Factors [ARFs] are transcription factors that bind with specificity to TGTCTC AuxREs. ARFs contain an amino-terminal DNA binding domain [DBD], and most ARFs contain a conserved carboxy-terminal domain [CTD] that facilitates their dimerization to themselves or Aux/IAA proteins. Amino acids located between ARF DBDs and CTDs are nonconserved and represent activation or repression domains. Specific ARFs can activate or repress auxin-responsive transcription by binding directly to TGTCTC AuxREs and may further potentiate transcriptional activation or repression by dimerizing with ARF(s) that are bound to AuxREs. While Aux/IAA proteins do not bind directly to TGTCTC AuxREs, they might also potentiate repression [or possibly activation] on AuxREs by forming heterodimers with ARF(s) that are bound to AuxREs. Major questions arise from the identification of many ARF and Aux/IAA proteins in Arabidopsis. How do specific ARFs with similar DNA binding domains target particular TGTCTC AuxREs? What governs the formation of specific pairs of ARFs, Aux/IAA, and ARF-Aux/IAA proteins? How do ARF and Aux/IAA homodimers and heterodimers determine whether an auxin response gene is activated or repressed? Does auxin play a role in targeting specific ARFs to TGTCTC AuxREs, in selecting the types of dimers that form, and/or in determining whether an activation or repression domain is functional when residing at an AuxRE? What other transcription and signalling factors participate along with ARFs and Aux/IAA proteins in regulating primary auxin response genes? The long term goal is to answer these questions and to begin to untangle the seemingly complex network of ARF and Aux/IAA interactions that must occur within cells to regulate auxin-responsive gene expression. The project has the following specific aims: (1) to determine if ARFs and Aux/IAA proteins show selectivity in interactions with one another; (2) to determine if auxin has an effect on ARF activation or repression domains directly or if an ARF CTD is required for auxin-responsive activation or repression; (3) to determine if Q-rich ARF activators play redundant roles in auxin-responsive gene expression; (4) to determine if the gene expression patterns of ARFs might restrict the types of ARF and Aux/IAA dimers that form in planta; and (5) to identify proteins besides Aux/IAAs that interact with ARFs and play roles in auxin signaling and auxin responses.