The plant hormone ethylene regulates many critical processes in plants including growth, fruit ripening, senescence, and shedding of leaves and petals. The first step in this signaling pathway is the binding of ethylene to receptors. Plants contain multiple ethylene receptor isoforms. The first to be isolated and the most studied is the ETR1 receptor from the model plant, Arabidopsis thaliana. Despite over a decade of study, the mechanisms for how the ETR1 receptor works are still unknown. The focus of this research project is to follow up on the recent observation from the Binder laboratory that the ETR1 receptor has multiple and unique functions. Loss of the ETR1 receptor isoform, but not other isoforms, causes loss of ethylene-stimulated nutations (oscillatory bending) yet results in more sensitive responses to ethylene for other traits such as inhibition of growth. These apparently contradictory results represent the first description of a non-overlapping role for an ethylene receptor. Therefore the PI will study the role of the ETR1 receptor in a new context to uncover more details about ethylene receptor function and output. To do this, the output of the ETR1 receptor that leads to nutations versus other traits will be delineated. There are three general aims to this project. The first is to determine whether or not there are multiple signaling pathways downstream of ETR1. The second aim is to ascertain which domains or sites on ETR1 are required for nutations versus other characteristics. Both of these objectives will be addressed using physiological analysis of mutants. The third aim is to determine whether or not the paradoxical role of ETR1 is caused by changes in the distribution of ETR1 within the growing plant. These studies will provide details about how ethylene receptors function to regulate multiple traits. This multifaceted project will transform our understanding about links between events at the molecular level with those at the organ level to give a broader understanding of how plants grow and develop.
Broader Impacts of the Project: This project will enhance research and educational infrastructure by broadening opportunities for undergraduate and graduate students to engage in research in the Binder lab. Dr. Binder also encourages high school students to engage in lab research. He participates in the University of Tennessee Pre-Collegiate Research Scholars Program that is a collaboration between The University of Tennessee and the Science Academy at Farragut High School in Knoxville. Currently one student is in the lab through this program and another was recruited from another high school independently. This project will enhance collaborations between the University of Tennessee and high schools in the area. This is an important element in educating future scientists. Student training will occur under the mentorship of Dr. Binder. In addition, Dr. Binder will continue to visit local classrooms to talk about biology research and will mentor for Planting Science (plantingscience.org), an on-line program that provides a learning and research resource in the plant sciences for K-16 students and teachers. All these activities will increase awareness about scientific research and ensure interested students become our future scientists. The increased understanding about ethylene signaling gained from this project will have profound impacts on a variety of crop related practices, most notably on post-harvest storage practices. This research will provide more focus so that specific responses to ethylene can be manipulated without compromising plant survival and vigor.
There were several major outcomes from the research funded by this award. First, we refined our knowledge of how the plant hormone ethylene binds to the receptors. This is of particular interest because ethylene is a gas and the mechanism for this binding will impact research on other gaseous signaling molecules. Second, we found several examples where members of the receptor family have non-overlapping functions. In some cases, this involves signaling from the receptor that is independent of ethylene which suggests these receptors may function in ways we did not appreciate. Finally, we found examples where the receptors signal to other hormone pathways. This is the first example of such cross-talk directly from the ethylene receptors. The findings of our research resulted in the publication of 15 papers. During the period of this award, time-lapse imaging setups used for these studies were integrated into acdtive learning units for the Plant Physiology and Molecular Biology Laboratory that I teach. These studies also included the training of 6 high school, 18 undergraduate, and 4 graduate students and 2 postdoctoral researchers. Of the high school and undergraduate students, 13 were women and 5 were from under-represented minorities. Thus, this award led to the training of many future scientists. Since ethylene affects many aspects of plant growth and development and impacts food production and storage, the findings from our research will influence our ability to increase food security.