Collaborative Research: Dynamic zonation in the plant root

植物的根在土壤中生长，从而在寻找养分和水分的同时锚定植物。正在生长的根尖分为两个主要区域：分生组织区和伸长区，分生组织区为根体产生新的细胞，伸长区细胞迅速伸长，从而推动根尖穿过土壤。这些功能生长区的分离是复杂的，因为这些区边缘的细胞改变了身份；也就是说，分生组织细胞变成了伸长细胞，伸长细胞变成了成熟细胞。因此，这些区域本质上是动态的，但保留了它们的位置。此外，当根对温度等因素做出反应时，这些带的长度、生长速度和细胞数量都会发生变化。一个耐人寻味的问题是，尽管存在潜在的细胞动力学，根是如何保持区域的完整性和稳定性的。这个问题正在实验中解决，使用遗传方法和温度变化来研究根的反应，成像生长和量化过程。这些研究将有助于解释这些区域是如何建立和调节的，提供关于根生长的机制和弹性的基本知识。研究结果可能为通过培育更具弹性的根系反应来改变根系生长提供新的工具，并可能为预测温度变化对根系行为的影响提供基线信息。本科生将接受培训，并将获得将工程学与生物学相结合以解决科学问题的跨学科方法的技能和经验。为了了解如何从动态细胞中产生稳定带，该项目使用了适应温度的拟南芥。首席研究员巴斯金在研究根的热形态发生时发现，尽管根在25摄氏度比15摄氏度生长得更快，但生长区的长度相同，皮层产生细胞的速度也相同。因此，生长带长度和皮层细胞产生率相适应，以抵消温度对反应的加速。有趣的是，适应的细胞产生率是皮质特有的：温度越高，表皮产生细胞的速度就越快。此外，当细胞分裂抑制物在皮质表达时，生长区被截断，但当在其他组织中表达时，生长区不被截断。该项目的目的是首先阐明在热形态发生过程中调控根分区的途径。通过比较15摄氏度和25摄氏度，该团队将筛选现有的突变株，确定相关基因是否直接作用于根，并获得专门针对表皮和皮质的转录本。第二个目的是阐明皮层在根分区中的作用。抑制细胞分裂的基因将从特定组织中的可诱导启动子中表达出来；然后，分裂、伸长和内复制将作为温度的函数进行量化。第三个目标将使用先进的图像分析来量化在两种温度下整个分生组织的细胞分裂率，显然是第一次解决不同组织中的分裂行为。总体而言，该项目将生长调节途径的分子解剖与细胞行为的定量分析相结合，以表征生命系统的分层组织。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Plant roots grow through the soil, thereby anchoring the plant while foraging for nutrients and water. The growing root tip is divided into two main regions: the meristem zone, which produces new cells for the root body, and the elongation zone, where cells elongate rapidly, thus propelling the root tip through the soil. The separation into these functional growth zones is complicated by the fact that cells at the edges of the zones change identity; that is, meristem cells become elongating cells and elongating cells become mature cells. These zones are therefore inherently dynamic, yet retain their location. In addition, as the root responds to factors such as temperature, the zones change in length, growth rate, and cell number. An intriguing question is how the root maintains the integrity and stability of the zones despite the underlying cell dynamics. This question is being addressed experimentally using genetic methods and temperature changes to study responses of the root, image the growth and quantify the processes. These studies will help explain how the zones are established and regulated, providing fundamental knowledge about the mechanisms and resilience of root growth. The outcomes could provide access to new tools for modifying root growth through breeding more resilient root responses and could provide baseline information for predicting impacts of temperature change on root behavior. Undergraduate students will be trained and will gain skills and experience in interdisciplinary approaches that integrate engineering with biology to solve scientific problems.To understand how stable zones emerge from dynamic cells, this project uses Arabidopsis thaliana acclimating to temperature. Investigating thermomorphogenesis in roots, principal investigator Baskin found that although the root grows faster at 25ºC compared to 15ºC, the growth zone has the same length and the cortex produces cells at the same rate. Thus, growth zone length and cortical cell production rate acclimate to counteract the acceleration of reactions by temperature. Interestingly, acclimated cell production rate is specific to cortex: epidermis produces cells faster at the warmer temperature. Also, the growth zone is truncated when an inhibitor of cell division is expressed in the cortex but not when expressed in other tissues. The project aims first to elucidate the pathway regulating root zonation during thermomorphogenesis. Comparing 15 and 25ºC, the team will screen extant mutants, determine whether implicated genes act in the root directly, and obtain transcriptomes specifically for epidermis and cortex. The second aim is to elucidate the role of the cortex in root zonation. Genes that inhibit cell division will be expressed from inducible promoters in specific tissues; then, division, elongation, and endoreduplication will be quantified as a function of temperature. The third aim will use advanced image analysis to quantify cell division rates throughout the meristem at both temperatures, resolving, apparently for the first time, division behavior in separate tissues. Overall, the project unites molecular dissection of growth-regulating pathways with quantitative analysis of cellular behavior to characterize the hierarchical organization of a living system.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.