A central control hub in DNA damage responses: function and regulation of the RBR module

DNA损伤对所有生物体中的每个细胞都是一个严重的威胁。在全球范围内，DNA损伤反应（DDR）由一系列严格调控的事件组成，从感知造成的损伤、激活DDR信号级联（也阻断细胞周期进程）、受损部位DNA修复因子的积累，到病变的物理修复和/或受损细胞的替换。值得注意的是，与动物相比，植物可以应对非常高浓度的有害物质。尽管这种明显的力量及其在不断变化的环境条件下与农业的相关性，但植物DNA修复途径尚未得到很好的理解。此外，酵母和动物的典型反应途径似乎只是部分保守，这就提出了植物如何如此有效地修复DNA损伤以及在这一过程中使用哪些调节因子的问题。在此背景下，双方的准备工作揭示了一个依赖拟南芥pRb同源物的DDR网络，称为视网膜母细胞瘤相关1 （RETINOBLASTOMA RELATED 1, RBR1）。RBR1似乎至少以两种方式起作用：首先，作为DDR基因的转录调节剂，其次，作为损伤部位修复复合物的潜在组装因子。因此，RBR1在DDR中起着中央控制枢纽的作用，因此为深入了解植物DDR的机制提供了一个独特的起点。本项目在完成RBR1结合位点全基因组鉴定和DNA损伤条件下RBR1蛋白-蛋白相互作用网络的基础上，结合双方互补的专业知识，了解RBR1靶点在DNA损伤时调控的分子机制，探索未知DDR相关RBR1靶基因的功能。同时，我们将研究RBR1本身是如何在DNA损伤时被调节的。由于双方的准备工作表明RBR1功能复合体及其几个靶基因的蛋白水解调控作用突出，因此本文特别强调这方面。为此，在大量准备数据的支持下，我们假设之前在两个合作伙伴的共同努力下发现的F-box蛋白FBL17在RBR1稳态中起核心作用，并且可能还参与了与DDR相关的RBR1靶点的选择性降解。

DNA damage represents a critical threat to every cell in all organisms. Globally, the DNA Damage Response (DDR) consists of a set of tightly regulated events, from sensing of the inflicted damage, activation of a DDR signalling cascade that also blocks cell cycle progression, accumulation of DNA repair factors at the damaged site, to the physical repair of the lesion and/or the replacement of damaged cells. Remarkably, plants can cope with very high concentrations of harmful agents in comparison to animals. Despite this apparent power and their relevance for agriculture under changing environmental conditions, the plant DNA repair pathways are not very well understood. Moreover, the canonical response pathways of yeast and animals appear to be only partially conserved raising the question of how plants can so efficiently repair DNA damage and which regulators are employed in this process. In this context, the preparatory work of both partners has revealed a DDR network relying on the Arabidopsis pRb homolog, called RETINOBLASTOMA RELATED 1 (RBR1). RBR1 appears to function in at least two ways: first, as a transcriptional regulator of DDR genes and second, as a potential assembly factor of repair complexes at the lesion sites. Thus, RBR1 acts as a central control hub in DDR and hence offers a unique starting point to get mechanistic insights into the DDR of plants. Following up on the genome-wide identification of RBR1 binding sites and the proteome-wide protein-protein interaction network of RBR1 under DNA damaging conditions, an aim of this project is to combine the complementary expertise of both partners to understand the molecular mechanism of how targets of RBR1 are controlled upon DNA damage and explore the function of unknown DDR related RBR1 target genes. At the same time, we will investigate how RBR1 itself is regulated upon DNA damage. Since the preparatory work of both partners indicated a prominent role of proteolytic regulation for both the RBR1 functional complex(es) as well as several of its target genes, special emphasis is put on this aspect. To that end, and supported by extensive preparatory data, we follow the hypothesis that the F-box protein FBL17, previously identified in collaborative effort of the two partners, plays a central role in RBR1 homeostasis and might be also involved in selective degradation of RBR1 targets involved in DDR.