Collaborative Research: Dynamic zonation in the plant root

植物的根在土壤中生长，因此在植物觅食养分和水分时锚定植物。生长的根尖分为两个主要区域：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。由于区域边缘的细胞改变了身份，这些功能性生长区域的分离变得更加复杂；即分生组织细胞变成伸长细胞，伸长细胞变成成熟细胞。因此，这些区域本质上是动态的，但保留了它们的位置。此外，随着根系对温度等因素的响应，区域的长度、生长速度和细胞数量也会发生变化。一个有趣的问题是，尽管潜在的细胞动力学，根是如何保持区域的完整性和稳定性的。这个问题正在通过实验解决，利用遗传方法和温度变化来研究根的反应，对生长过程进行成像和量化。这些研究将有助于解释这些区域是如何建立和调节的，提供有关根系生长机制和恢复力的基本知识。这些结果可以为通过培育更有弹性的根系响应来调节根系生长提供新的工具，并可以为预测温度变化对根系行为的影响提供基线信息。本科学生将接受培训，并获得跨学科方法的技能和经验，将工程与生物学结合起来解决科学问题。为了了解稳定区是如何从动态细胞中出现的，该项目使用拟南芥适应温度。在研究根的热形态发生时，首席研究员巴斯金发现，尽管根在25ºC下比在15ºC下生长得更快，但生长带的长度和皮层产生细胞的速度相同。因此，生长带的长度和皮层细胞的生成速率适应了温度对反应加速的影响。有趣的是，适应环境的细胞生成速率是皮层特有的：在较温暖的温度下，表皮产生细胞的速度更快。同样，当细胞分裂抑制剂在皮层中表达而在其他组织中表达时，生长带被截断。该项目首先旨在阐明在热形态形成过程中调节根分区的途径。比较15ºC和25ºC，研究小组将筛选现存的突变体，确定相关基因是否直接作用于根，并获得表皮和皮层的特异性转录组。第二个目的是阐明皮层在根区化中的作用。抑制细胞分裂的基因将在特定组织中通过诱导启动子表达；然后，分裂、延伸和内重复数将被量化为温度的函数。第三个目标将使用先进的图像分析来量化两种温度下整个分生组织的细胞分裂率，这显然是第一次解决单独组织中的分裂行为。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结合起来，以表征生命系统的分层组织。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.