CAREER: Permissive acidity as a regulator of plant cell expansion

植物生命对于地球和地球上的所有生命的健康和福祉是必不可少的。因此，了解控制植物生长的过程对于确保地球和人类生活的未来至关重要。在这个项目中，将在幼苗中研究“酸生长”的控制机制，这是植物生命中允许从土壤中萌发的关键生长阶段。酸生长是指植物细胞周围的细胞壁变得更酸性的一种机制；酸性环境激活细胞壁的变化，使其更容易变形，从而允许其周围的植物细胞扩张并导致生长。细胞壁的酸化是由一种名为生长素的植物激素启动的。然而，过多的生长素会抑制生长，这表明酸生长的一个更复杂的机制正在发挥作用。在这个项目中，我们将扩展酸生长模型，以更好地解释生长素和壁酸度对生长的调节；我们将研究生长的“允许酸度”的可能性，在这种情况下，壁可能太碱性和太酸性而不能导致生长。该项目包括为即将到来的转学学生开发和实施一项名为“Emerge”的暑期研究计划。Emerge项目将让五名学生在大三前的暑假从事与苗木生长相关的研究项目。Emerge计划将为即将到来的转学学生提供研究经验和社区，这是成功完成学位的关键因素。酸生长假说是在50多年前提出的；该假说指出，生长素导致细胞壁酸化，从而导致细胞壁松弛和细胞扩张。然而，近100年来，我们已经知道，太多的生长素会抑制生长，太多的酸度也会抑制生长。使用黑暗生长的拟南芥下胚轴作为伸长的模型系统，我们将研究一个包含允许酸度概念的扩展酸生长模型：存在一个适合细胞生长的最佳酸性pH，太碱性或太酸性可能导致生长停止。我们将在器官和细胞水平上量化暗生长下胚轴伸长过程中细胞生长、壁酸和生长素反应之间的关系。此外，我们将利用原子力显微镜探索生长、生长素、pH和细胞壁机械参数(弹性、粘弹性和屈服强度)之间的定量关系。我们还将对植物中几种壁面修饰蛋白的pH依赖活性进行参数化。所有这些数据将被用来建立基于有限元方法的伸长下胚轴的机械生长模型，该模型由明确的生长素分布指导。该项目还包括一项针对即将入学的转校生的暑期研究寄宿计划，名为“Emerge”。每年夏天，在传统的秋季招生开始之前，Emerge计划将有5名学生共同参与一个项目，以启动他们的研究经验和教育，并在生命科学领域内的转学学生群体中建立社区。该奖项由生理机制和生物力学计划以及生物科学理事会综合组织系统部门的植物、真菌和微生物发育机制计划共同资助。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 life is essential for the health and well-being of the planet, and all life therein. Understanding the processes that control growth in plants is therefore essential for ensuring the future of the planet and human life. In this project, the ‘acid growth’ control mechanism will be investigated in young seedlings, a key growth stage in the plant’s life that allows for emergence from the soil. Acid growth refers to a mechanism whereby the cell wall surrounding the plant cell becomes more acidic; an acidic environment activates changes in the cell wall that make it more deformable, thus allowing the plant cell it surrounds to expand and resulting in growth. The acidification of the cell wall is turned on by a plant hormone called auxin. However, too much auxin inhibits growth indicating a more complex mechanism for acid growth is at play. In this project we will extend the acid growth model to better explain the regulation of growth by auxin and wall acidity; we will investigate the possibility of a ‘permissive acidity’ for growth where the wall can be too basic and too acidic to result in growth. This project includes the development and implementation of a summer research program for incoming transfer students called ‘EMERGE’. The emerge program will have a group of five students working on a seedling growth-related research project during the summer before their junior year. The EMERGE program will provide research experience and community for incoming transfer students, key aspects for successful degree completion.The Acid Growth hypothesis was proposed over 50 years ago; it states that auxin leads to cell wall acidification which leads to wall relaxation and cell expansion. However, for almost 100 years we have known that too much auxin inhibits growth, as does too much acidity. Using the dark-grown Arabidopsis thaliana hypocotyl as a model system for elongation, we will investigate an expanded acid growth model that encompasses the concept of permissive acidity: there is an optimal acidic pH for cell growth and being too basic or too acidic may result in cessation of growth. We will quantify the relationships between cell growth, wall acidity, and auxin response during dark-grown hypocotyl elongation at both organ and cell levels. Furthermore, we will explore the quantitative relationship between growth, auxin, pH, and cell wall mechanical parameters (elasticity, viscoelasticity, and yield strength) using atomic force microscopy. We will also parameterize the pH dependent activity of several wall modifying proteins in planta. All of this data will be used to build a finite element method-based mechanical growth model of the elongating hypocotyl, instructed by an explicit auxin distribution. This project also includes a summer research on-boarding program for incoming transfer students called ‘EMERGE’. The EMERGE program will have cohorts of 5 students working on a project together each summer before traditional Fall enrollment begins in order to jump-start their research experience and education and to build community within the transfer student population within Life Sciences.This award is co-funded by the Physiological Mechanisms and Biomechanics Program and the Plant, Fungal, & Microbial Developmental Mechanisms Program in the Division of Integrative Organismal Systems, Directorate for Biological Sciences.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.