Elucidating the function of the CYBDOM protein HYP1 in phosphorus deficiency-dependent primary root growth

土壤养分的有效性对根系的生长发育有很大的影响。除了由单一营养物质引发的影响外，不同元素的相互作用也可以作为改变根发育过程的线索。最近的研究表明，过渡金属铁(Fe)可以通过在缺磷植物根尖区启动复杂的氧化还原反应和信号转导事件来抑制低磷(P)响应下的根伸长。然而，在缺磷的根中，铁依赖的氧化还原活性的机制仍然知之甚少。通过将转录学、生物信息学和反向遗传学相结合，我们在拟南芥中鉴定了一种新的细胞色素b561/多巴胺β-单加氧酶N末端(CyBDOM)蛋白，该蛋白被预测为通过胞质抗坏血酸作为电子供体来驱动质外体氧化还原反应。我们的初步工作表明，我们所鉴定的蛋白质，我们命名为对低P_1超敏感(HYP1)，对于在低P有效性下维持根的生长是至关重要的。因此，本项目的主要目标是：i)确定HYP1和其他调节低磷下根生长的分子成员之间的遗传联系，并评估HYP1在特定根区的定位如何影响该蛋白不表达区域的细胞生物学反应；ii)表征缺磷根中依赖HYP1和抗坏血酸的氧化还原变化，并研究HYP1在质外体中铁还原或抗坏血酸再生中的作用；以及iii)确定HYP1的生化功能以及该蛋白的细胞色素b561核心和Domon结构域之间的功能相互作用。为了实现这些目标，我们将把基因工具与组织化学、细胞生物学、生化和药理学方法结合起来。这项研究的发现将有助于阐明通过CyBDOMs进行的抗坏血酸依赖的跨膜电子传递的生理功能。此外，HYP1的特性将为通过调控根质外体氧化还原活性来提高根的抗逆性提供一种手段。

The availability of nutrients in soils has a strong impact on root growth and development. Apart from effects triggered by single nutrients, also the interaction of different elements can act as a cue to modify root developmental processes. Recent studies have shown that the transition metal iron (Fe) can inhibit root elongation in response to low phosphorus (P) by initiating a complex interplay of redox reactions and signaling events in the root apical zone of P-deprived plants. However, still little is known about the mechanism underlying Fe-dependent redox activity in P-deficient roots. By combining transcriptomics with bioinformatics and reverse genetics in Arabidopsis thaliana we identified a novel cytochrome b561/dopamine beta-monooxygenase N-terminal (CYBDOM) protein, which is predicted to drive apoplastic redox reactions by using cytosolic ascorbate as an electron donor. Our preliminary work demonstrated that the identified protein, which we named HYPERSENSITIVE TO LOW P 1 (HYP1), is crucial for maintaining root growth on low P availability. Thus, the main objectives of this project are: i) to determine the genetic link between HYP1 and other molecular players that adjust root growth under low P and to assess how HYP1 localization in specific roots zones affects cell biological responses in zones where this protein is not expressed; ii) to characterize HYP1- and ascorbate-dependent redox changes in P-deprived roots and to investigate the role of HYP1 in ferric Fe reduction or ascorbate regeneration in the apoplast; and iii) to determine the biochemical function of HYP1 and the functional interplay between the protein’s cytochrome b561 core and the DOMON domain. To achieve these goals, we will combine genetic tools with histochemical, cell biological, biochemical and pharmacological methods. The findings of this research will shed light on the physiological function of yet poorly characterized ascorbate-dependent trans-membrane electron transport via CYBDOMs. Furthermore, the characterization of HYP1 will provide a means to improve root stress tolerance by manipulating root apoplastic redox activity.