Deciphering the roles and mechanisms of ethylene-independent ACC action in plants

University Of Maryland, College Park, College Park MD

Investigators

Abstract

The plant hormone ethylene regulates numerous physiological responses of agronomic importance. Plants produce ethylene from a molecule called 1-aminocyclopropane-1-carboxylic acid (ACC). Separate from ACC’s central role in ethylene biosynthesis, there is growing evidence that ACC itself can trigger its own responses in plants, and there is preliminary evidence that the signaling pathways for ACC involve metabolite signaling, which is a relatively unexplored topic in plant biology. This project seeks to define the ethylene-independent roles of ACC and to elucidate the potentially novel molecular mechanisms underlying the process of ACC signaling. The project uses a combination of approaches, including metabolomics, transcriptomics, and molecular genetics, and employs two different plant model systems, a flowering plant and a non-flowering plant (a liverwort). The results of the project are expected to elucidate the mechanisms of ACC signaling, enhance our understanding of ACC and ethylene hormone biosynthesis, provide an evolutionary perspective on the mechanisms of ACC action, and lay the foundation for incorporating ACC and metabolite signaling into revised mechanistic models of plant growth and development. The Broader Impacts of this project include the intrinsic merit of the research as all flowering plants use ACC/ethylene to control critical agronomic traits such as fruit ripening. Additional work will provide science education for students, teachers, and the general public, with an emphasis on the engagement of students from all backgrounds. These experiential learning activities take place in high school classrooms, college classrooms, research laboratories, and public science centers. Growing evidence indicates that the biological precursor of the plant hormone ethylene, ACC, is a novel signal capable of inducing a variety of responses independent of its central role in ethylene biosynthesis. Preliminary data indicate that responses to ACC likely involve complex mechanisms, given the detection of significant metabolomic changes when ACC biosynthesis is perturbed. The project goals are to define the ethylene-independent roles of ACC and elucidate the underlying mechanisms of ACC-induced responses. The researchers will investigate the hypothesis that ACC acts at least in part through metabolic changes detected by mass spectrometry in Arabidopsis thaliana as well as the bryophyte Marchantia polymorpha, which does not use ACC as an ethylene precursor. They also analyze the biological and metabolic consequences when A. thaliana plants lack the ability to synthesize ACC. These studies will provide insight into the evolutionary history of ACC function and advance the relatively unexplored topic of metabolite signaling in plants. The project also examines the molecular genetic basis of a specific A. thaliana response to ACC (lateral root formation) in A. thaliana, and similarly explores ACC responses in M. polymorpha starting from transcriptomic data. Taking a broader approach, the researchers genetically dissect the underlying mechanisms of ACC responses by cloning and analyzing the genes/gene products corresponding to ACC-insensitive mutants in both A. thaliana and M. polymorpha. The project’s findings should provide new perspectives on ACC and ethylene biosynthesis and lay the foundations for incorporating ACC and metabolite signaling into mechanistic models of plant growth and development. 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.