Auxin in transcription factor complex controls polarity in plant organogenesis

包括植物和动物在内的多细胞生物发育出专门的器官，这些器官由不同类型的组织组成。器官的结构或模式是由组织内沿沿着对称轴的极性决定的。为了协调组织或器官的极性，多细胞生物使用移动的物质，如激素。植物激素生长素是最早被研究的激素之一，查尔斯达尔文和他的儿子弗朗西斯在19世纪80年代研究了生长素对光调节植物生长（向光性）的影响。然而，直到20世纪30年代，生长素分子才被分离出来，其分子结构被确定为吲哚-3-乙酸（IAA）。在植物中，生长素在启动器官形成和在特定组织类型中使器官形成图案中起重要作用，包括例如侧根、幼叶和雌性生殖器官雌蕊群的那些。生长素动力学的控制是在生物合成、运输和信号传导水平上实现的。生长素分子先前被证明介导特定蛋白质之间的相互作用，从而导致基因表达抑制物的降解。它也已被确定，生长素可以通过抑制PIN生长素转运蛋白的内化来影响其自身的运输。虽然这些生长素信号传导机制可以解释生长素作用的许多过程，但可能存在其他转录信号传导途径来解释生长素发挥作用的众多过程。我们已经确定了在模式植物拟南芥中发现的两种蛋白质之间的相互作用，这两种蛋白质都是花的雌蕊群中极性的关键调节因子。它们被命名为ETTIN和IND，两者都作为转录因子（即直接控制基因的表达）。从在酵母中进行的实验中，我们知道这些蛋白质可以在所谓的受体复合物中物理结合生长素，我们的初步数据表明，ETT和IND的靶基因组在结合生长素时发生变化。这表明存在生长素的替代信号通路。ETTIN控制其他植物器官的启动和模式化，根据这一点，我们确定了其他转录因子，ETT可以以类似的生长素敏感的方式相互作用。因此，这种新途径可能在植物发育中是保守的。通过本提案中描述的实验，我们的目标是对这个新发现的生长素信号传导模块达成一种机制和发展性的理解，该模块可能特别适合于在整个植物发育过程中促进极性的精确切换。

Multicellular organisms including plants and animals develop specialised organs, which are composed of different types of tissues. The structure - or pattern - of organs is determined by the polarity within tissues along axes of symmetry. In order to coordinate polarity across a tissue or organ, multicellular organisms use mobile substances such as hormones. The plant hormone auxin was one of the first hormones ever to be studied and the effect of auxin on light-regulated plant growth (phototropism) was investigated by Charles Darwin and his son Francis in the 1880s. It was, however, not until the 1930s that the auxin molecule was isolated and its molecular structure determined as indole 3-acetic acid (IAA). In plants, auxin plays an essential role in initiating organ formation and in patterning the organs in specific tissue types, including for example lateral roots, young leaves and those of the female reproductive organ, the gynoecium. Control of auxin dynamics is achieved at the levels of biosynthesis, transport and signalling. The auxin molecule was previously shown to mediate the interactions between specific proteins thereby causing the degradation of repressors of gene expression. It has also been established that auxin can influence its own transport via inhibiting internalisation of PIN auxin transporters. Although these mechanisms of auxin signalling can explain many processes of auxin action, other transcriptional signalling pathways are likely to exist to account for the plethora of processes in which auxin plays a role. We have identified an interaction between two proteins found in the model plant Arabidopsis, which both are key regulators of polarity in the gynoecium of the flower. They have been named ETTIN and IND and both act as transcription factors (i.e. directly control the expression of genes). From experiments carried out in yeast we know that together these proteins can physically bind auxin in a so-called receptor complex, and our preliminary data suggest that the target gene set of ETT and IND changes when they bind auxin. This suggests the existence of an alternative signalling pathway for auxin. ETTIN controls the initiation and patterning of other plant organs, and in accordance with this, we identified other transcription factors that ETT can interact with in a similar auxin-sensitive manner. It is therefore likely that this new pathway is conserved in plant development. Through experiments described in this proposal, we aim to reach a mechanistic and developmental understanding of this newly discovered auxin-signalling module, which may be particularly well suited to facilitate precise switches in polarity throughout plant development.