Decoding the Lateral Expansion of Plant Stems

在动物中，成年个体的组织增殖往往是病理性的和有害的，与之相反，植物已经进化出一种无限期的生长习惯。在这方面特别值得注意的是植物茎和根的增厚，因为这是一个纯粹的胚胎后生长过程，而负责的干细胞群形成层嵌入在高度分化的组织中。因此，植物横向生长必须整合和克服周围组织所隐含的物理限制，并诱导其性质的根本变化。参与其中的组织是如何相互沟通以建立如此复杂的生长过程的，这是完全未知的。在这里，我们将探讨参考植物拟南芥的侧茎生长过程，作为胚胎后生长过程的范例。我们将通过分析每个单一茎组织在横向生长开始之前和之后的转录组来研究细胞行为。细胞壁固定了植物细胞之间的相对位置，其刚性对植物体的机械支撑至关重要。因此，我们将进一步研究细胞壁修饰在植物侧生调控中的作用，并利用正向遗传学鉴定将细胞壁状态转化为细胞动力学变化的新型信号级联。总之，这些方法将对侧枝生长提供前所未有的见解，这是一个负责木材生产和大量陆地生物量积累的过程。因此，该项目将系统地描述一个未被充分探索但核心的植物器官的发展，并揭示多细胞生物生长过程的基本概念。

In contrast to animals in which tissue proliferation in adult individuals is often pathological and deleterious, plants have evolved an indefinite growth habit. Especially remarkable in this respect is the thickening of plant stems and roots, as this is a pure postembryonic growth process and the responsible group of stem cells, the cambium, is embedded in highly differentiated tissues. Consequently, lateral plant growth has to integrate and overcome physical constraints implied by surrounding tissues and induce a fundamental change in their properties. How participating tissues communicate to establish such a complex growth process is completely unknown. Here we will explore the process of lateral stem growth in the reference plant Arabidopsis thaliana as a paradigm for postembryonic growth processes. We will study cell behavior by profiling the transcriptomes of each single stem tissue before and after lateral growth initiation. Cell walls fix the position of plant cells relative to each other and their rigidity is essential for mechanical support of the plant body. Therefore, we will additionally investigate the role of cell wall modifications in the regulation of lateral plant growth and identify by use of forward genetics novel signaling cascades that translate cell wall states into changes in cellular dynamics. Together, these approaches will provide unprecedented insight into lateral stem growth, a process responsible for wood production and the accumulation of a large proportion of terrestrial biomass. Thereby, this project will systemically characterize the development of an underexplored but central plant organ and reveal fundamental concepts of growth processes in multicellular organisms.