Role of cyclin-dependent kinase inhibitors (KRPs) in root meristem activation

植物的生长在几个方面与动物不同。植物在其一生中不断生长，形成新叶和新花，这种特性取决于位于芽和根尖端的分生组织区域的干细胞，与大多数细胞分裂发生有关。与动物的另一个重要区别是，成熟的胚胎在静止状态下被包裹在种子中，允许传播和生存。在有利的条件下，萌发发生。此时，幼苗顶端的分生组织内的细胞必须重新开始分裂。几天后，幼苗的主根长出侧根或侧根。侧根由特化的细胞恢复分裂形成新的分生组织，然后产生侧根。这些对于将植物固定在土壤中以及吸收水分和养分的能力非常重要。总之，发芽和侧根形成是植物和作物成功生长和竞争能力的重要方面，而幼苗建立的这些关键过程都需要激活细胞分裂。我们实验室的研究重点是植物细胞分裂是如何被调控的。细胞分裂是由一系列称为细胞周期的事件控制的。细胞致力于分裂的主要检查点被称为G1，可以被称为细胞周期蛋白和KRPs的蛋白质调节。这种特殊类型的细胞周期蛋白被称为CYCD。细胞周期蛋白刺激细胞分裂，而KRP蛋白可以与细胞周期蛋白结合，从而抑制细胞分裂。虽然KRP蛋白已经被研究过，但我们对它们在根部细胞分裂激活过程中的作用知之甚少。这是因为现有的研究过度表达了这些基因，导致非常高的水平，可能掩盖了它们的特定功能。相比之下，我们研究了这些基因的突变，发现它们具有特定的作用。其中一个基因决定发芽时细胞分裂的时间，另一个基因控制侧根的数量。因此，在一个突变体中，种子发芽更快，在第二个突变体中，幼苗有更多的侧根。我们还发现了KRP蛋白的一种新功能。我们发现，在一个突变体中，一个特定的CYCD蛋白不再定位于细胞核，而是定位于细胞的细胞质中。这意味着KRP蛋白需要携带CYCD进入它起作用的细胞核。由于其余六个KRP基因仍然存在于突变体中，这表明KRP和CYCD之间存在特定的相互作用，可以解释我们观察到的影响。在这个项目中，我们想要了解KRP基因及其编码的蛋白质如何影响细胞分裂的激活，而细胞分裂在幼苗早期生长中起着如此重要的作用。我们将研究不同的突变体及其对发芽和侧根形成的影响。我们将分析它们的功能，并特别关注我们发现的KRPs在CYCD蛋白核转运中的新作用。因此，我们将更好地了解细胞分裂、发芽和侧根形成是如何由细胞周期调节蛋白控制的。

Plant growth is different to that of animals in several ways. Plants grow continuously forming new leaves and flowers throughout their lifespan, and this property depends on stem cells located in the tips of shoots and roots in regions known as meristems, associated with which most cell division occurs. Another important difference to animals is that the mature embryo is packaged into the seed in a quiescent state, allowing dispersal and survival. Under favorable conditions, germination occurs. At this point, cells within the meristems at the tip of the seedling shoot and root must start dividing again. A few days later, lateral or side roots form from the main root of the seedling. These arise from specialised cells which resume division to form a new meristem that will then produce the lateral root. These are important in anchoring the plant in the soil, and its ability to take up water and nutrients. Together, germination and lateral root formation are essential aspects of the ability of plants and crops to grow and compete successfully, and these key processes in seedling establishment both require the activation of cell division. The research in our lab focuses on how cell division in plants is regulated. Cell division is controlled by a series of events called the cell cycle. The main check-point where the cell commits itself to division is called G1 and can be regulated by proteins called cyclins and KRPs. The particular type of cyclin involved is called CYCD. Cyclins stimulate cell division, whereas KRP proteins can bind to cyclins and thereby inhibit cell division. Although KRP proteins have been studied, we do not know much about their role in the processes required for activation of cell division in the roots. This is because existing studies have overexpressed these genes, resulting in very high levels that may mask their specific functions. In contrast, we have studied mutants of these genes and found that they have specific roles. One is required for the timing of cell division in germination, and a second controls the number of lateral roots produced. In one mutant, seeds therefore germinate faster, in the second the seedlings have more lateral roots. We have also discovered a new function for KRP proteins. We found that in one mutant, a specific CYCD protein is no longer localized in the nucleus but in the cytoplasm of the cell. This means that the KRP protein is required to carry the CYCD into the nucleus where it acts. Since the remaining six KRP genes are still present in the mutant, this suggests a specific interaction between KRP and CYCD that can explain the effects we have observed. In this project, we want to understand how KRP genes and the proteins they encode affect the activation of cell division that plays such a important role in early seedling growth. We will study the different mutants and how they are affected in germination and lateral root formation. We will analyse how they function and in particular focus on the new role we have discovered for KRPs in the nuclear transport of CYCD proteins. As a result, we will have a better understanding of how cell division, germination and lateral root formation is controlled by cell cycle regulatory proteins.