CAREER: Permissive acidity as a regulator of plant cell expansion

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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.