Cross-talk between Copper Homeostasis and Plant Development

由于其强大的化学性质，铜、锌和铁等几种金属在进化过程中被选择为所有生物生命所必需的许多蛋白质的必要辅助因子。植物面临的挑战是，在大多数土壤中，这些必需营养素的生物可利用浓度通常很低，而且往往很有限。因此，可以想象，并得到一些零散实验证据的支持，金属营养状况也可能对植物的发育过程产生调节作用。然而，针对这一问题和潜在调控机制的有针对性的研究很少，而且在植物发育研究中，金属的可用性很少被调整到自然环境中常见的水平，甚至很少被控制。植物铜（Cu）营养状况对花的育性和开花时间有很大影响，但其分子基础尚不清楚。虽然一些拟南芥启动子结合蛋白样（SPL）家族转录因子与植物发育过程有关，但拟南芥spl7突变体在控制大量中央缺铜反应的转录因子中存在缺陷。这些突变体在生理上也比野生型更缺铜。此外，spl7突变体的开花时间对Cu缺乏的响应是强烈异常的。本文拟在分子水平上阐明铜稳态与开花时间调控之间的相互作用，以及铜稳态网络与内源糖响应之间的调控关系。我们将采用微量营养素控制的生长条件，深入分析植物Cu状态和SPL7功能丧失对开花时间的影响。随后，我们将采用反向遗传方法来剖析铜营养状况、铜稳态网络和花期调控网络之间的相互作用。我们将讨论SPL转录因子亚群的功能，该亚群迄今尚未被很好地表征，也不是microRNA156的目标，在Cu稳态和植物发育的金属依赖性调节中。这项工作将揭示调控过程如何依赖于植物的Cu营养状态，Cu是一种重要的过渡金属，其特征是与所有营养金属阳离子中配体分子的结合最强。进一步了解铜稳态网络与开花时间控制之间的相互作用，将扩大我们对植物发育代谢控制的认识。最后，这项工作将有助于在生物可利用铜缺乏的土壤上提高作物产量和产量质量，这些土壤约占耕地面积的五分之一。

As a result of their potent chemical properties, several metals such as copper, zinc and iron have been selected during evolution for roles as essential cofactors of numerous proteins indispensable for all biological life. Plants are faced with the challenge that in most soils, bioavailable concentrations of these essential nutrients are generally very low, and often limiting. Hence it is conceivable, and supported by some scattered experimental evidence, that metal nutrient status might exert a regulatory influence also on developmental processes in plants. However, targeted studies addressing this and the underlying regulatory mechanisms are scarce, and metal availability has rarely been adjusted to levels common in natural environments, or even controlled, in research on plant development. Plant copper (Cu) nutritional status strongly affects flower fertility and flowering time, but the molecular basis for this is not understood. Whereas several Arabidopsis thaliana Squamosa Promoter binding protein-Like (SPL) family transcription factors have been implicated in plant developmental processes, Arabidopsis thaliana spl7 mutants are defective in a transcription factor that controls a large set of central Cu deficiency responses. These mutants are also physiologically more Cu-deficient than the wild type. Moreover, the response of flowering time to Cu deficiency is strongly aberrant in spl7 mutants. Here we propose to elucidate at the molecular level the cross-talk between Cu homeostasis and flowering time control, as well as the regulatory relationships between the Cu homeostasis network and responses to endogenous sugars. We will employ micronutrient-controlled growth conditions for an in-depth analysis of the influence of plant Cu status and loss of SPL7 function on flowering time. Subsequently, a reverse genetic approach will be pursued to dissect the interactions between Cu nutritional status, the Cu homeostasis network and the regulatory network of flowering time control. We will address the functions of the subgroup of SPL transcription factors which is less well characterized to date and not targeted by microRNA156, in Cu homeostasis and metal-dependent modulation of plant development. This work will reveal how regulatory processes can be triggered dependent on plant nutrient status of Cu, an essential transition metal distinctive by the strongest binding to ligand molecules out of all nutrient metal cations. An improved understanding of the interaction between the copper homeostasis network and flowering time control will expand our knowledge of the metabolic control of plant development. Finally, this work will be instrumental for increasing crop yields and yield quality on soils deficient in bioavailable Cu, which comprise approximately one fifth of the cultivated area.