Department of Molecular Signal Processing, Leibniz Institute of Plant Biochemistry (IPB), Halle (Saale) D-06120, Germany.
Institute of Agricultural and Nutritional Sciences, Martin Luther University Halle-Wittenberg, Halle (Saale) D-06120, Germany.
Nat Commun. 2017 Jun 7;8:15706. doi: 10.1038/ncomms15706.
Auxin is a small molecule morphogen that bridges SCF-AUX/IAA co-receptor interactions leading to ubiquitylation and proteasome-dependent degradation of AUX/IAA transcriptional repressors. Here, we systematically dissect auxin sensing by SCF-IAA6 and SCF-IAA19 co-receptor complexes, and assess IAA6/IAA19 ubiquitylation in vitro and IAA6/IAA19 degradation in vivo. We show that TIR1-IAA19 and TIR1-IAA6 have distinct auxin affinities that correlate with ubiquitylation and turnover dynamics of the AUX/IAA. We establish a system to track AUX/IAA ubiquitylation in IAA6 and IAA19 in vitro and show that it occurs in flexible hotspots in degron-flanking regions adorned with specific Lys residues. We propose that this signature is exploited during auxin-mediated SCF-AUX/IAA interactions. We present evidence for an evolving AUX/IAA repertoire, typified by the IAA6/IAA19 ohnologues, that discriminates the range of auxin concentrations found in plants. We postulate that the intrinsic flexibility of AUX/IAAs might bias their ubiquitylation and destruction kinetics enabling specific auxin responses.
生长素是一种小分子形态发生素，它连接 SCF-AUX/IAA 共受体相互作用，导致 AUX/IAA 转录阻遏物的泛素化和蛋白酶体依赖性降解。在这里，我们系统地剖析了 SCF-IAA6 和 SCF-IAA19 共受体复合物对生长素的感应，并评估了体外的 IAA6/IAA19 泛素化和体内的 IAA6/IAA19 降解情况。我们表明，TIR1-IAA19 和 TIR1-IAA6 具有不同的生长素亲和力，这与 AUX/IAA 的泛素化和周转率动态相关。我们建立了一个系统来跟踪体外 IAA6 和 IAA19 中的 AUX/IAA 泛素化，并表明它发生在具有特定赖氨酸残基的、侧翼降解序列的柔性热点上。我们提出，在生长素介导的 SCF-AUX/IAA 相互作用中，这种特征被利用。我们提出了一个不断进化的 AUX/IAA 库的证据，以 IAA6/IAA19 同系物为例，该证据区分了植物中存在的生长素浓度范围。我们推测，AUX/IAAs 的固有灵活性可能会影响它们的泛素化和破坏动力学，从而实现特定的生长素反应。
