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、顶端优势和维管组织形成中发挥重要作用。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)生长素反应基因表达模式的调控。早期生长素应答基因含有一个或多个生长素应答元件[AuxREs]，其中含有序列TGTCTC，该序列赋予启动子生长素应答能力。生长素反应因子[ARF]是与TGTCTC AuxREs特异性结合的转录因子。ARF含有一个氨基末端DNA结合域[DBD]，而大多数ARF含有一个保守的羧基末端结构域[CTD]，便于它们二聚为自身或AUX/IAA蛋白。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。特定的ARF可以通过直接与TGTCTC AuxREs结合来激活或抑制生长素反应的转录，并可能通过与AuxREs结合的ARF(S)二聚来进一步增强转录激活或抑制。虽然AUX/IAA蛋白不直接与TGTCTC AuxREs结合，但它们也可能通过与Arf(S)形成与AuxREs结合的异源二聚体来增强对AuxREs的抑制[或可能激活]。在拟南芥中，许多ARF和AUX/IAA蛋白的鉴定是一个主要问题。具有相似DNA结合域的特定ARF如何靶向特定的TGTCTC AuxRE？是什么控制特定的ARF、AUX/IAA和ARF-AUX/IAA蛋白对的形成？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？生长素是否在靶向TGTCTC AuxRE的特定ARF、选择形成的二聚体类型和/或确定激活或抑制结构域在AuxRE上是否起作用？还有哪些转录和信号因子与ARF和AUX/IAA蛋白一起参与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ARF和AUX/IAA相互作用的看似复杂的网络，这些相互作用必须发生在细胞内，以调节生长素反应基因的表达。该项目有以下具体目标：(1)确定ARF和AUX/IAA蛋白在相互作用中是否表现出选择性；(2)确定生长素是否直接影响ARF激活或抑制结构域，或者是否需要ARF CTD来激活或抑制生长素；(3)确定富含Q的ARF激活子是否在生长素响应基因表达中扮演多余的角色；(4)确定ARF的基因表达模式是否可能限制在植物中形成的ARF和AUX/IAA二聚体的类型；以及(5)鉴定AUX/IAA以外与ARF相互作用并在生长素信号转导和生长素反应中发挥作用的蛋白质。

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.