Binder Lab
Having a gas with science at the UT-Knoxville since 2008

Office: 343 Hesler Biology Building (865) 974-7994
Lab: 106 Hesler Biology Building
(865) 974-7997

Dept. of Biochemistry, Cellular and Molecular Biology
Genome Science & Technology Program

University of Tennessee-Knoxville


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Research Focus:

Ethylene is a plant hormone that influences many developmental and physiological processes in plants such as growth, senescence, abscission, fruit ripening, and responses to stresses. It is the basis of the saying one bad apple spoils the bunch because of its role in fruit ripening. Research in this lab focuses on ethylene signal transduction with a major focus on understanding the roles and functions of the receptors for ethylene in plants as well as how ethylene receptors function in bacteria. We combine imaging techniques with biochemistry, molecular biology, computational and mathematical modeling, and genetics to unravel the complexities of ethylene signaling. There are several aspects of ethylene signaling we are currently pursuing.

Structure-Function of the Ethylene Binding Domain
One topic of interest is to further define the structure and function of the ethylene binding domain. We have used both mutational and chemical analyses to uncover more information about how ethylene binds to the receptor and transduces the signal through the protein. Interestingly, ethylene receptors are metalloproteins containing copper ions. While copper is the natural co-factor, we have shown that the other group 11 transition metals (silver and gold) support ethylene binding to the receptors, whereas, other metals do not. This observation is of interest because silver, but not gold, blocks ethylene action in the plant. These observations led to the hypothesis that silver may block conformational changes in the receptor because it is larger than copper. Interestingly, silver mainly affects the ETR1 ethylene receptor, but not the other isoforms. Another chemical approach we have used is to analyze ethylene binding and receptor function in the presence of various strained alkenes and other small chemicals in order to better define the ethylene binding pocket, identify how copper is delivered to the receptors, and uncover useful chemicals that can be used agriculturally. Finally, we have used mutagenesis of conserved residues in the binding domain to define regions necessary for ethylene binding, turning the receptor off when ethylene binds, and maintaining a functional receptor. For more information refer to: Rodriguez et al., 1999; Wang et al., 2006; Binder et al., 2007; Pirrung et al., 2008; Binder et al., 2010; McDaniel and Binder, 2012; Li et al. 2017).

Ethylene Growth Response Kinetics and Signaling Network Toplogies
A second area is to uncover new details about the ethylene signal transduction pathway downstream of the receptors. We use a computer-driven, time-lapse image acquisition system to study the kinetics of growth changes in etiolated seedlings of Arabidopsis thaliana. This method has revealed transient and subtle changes due to ethylene that would have otherwise remained unknown (list of lab papers using this technique). Combining this approach with genetics and molecular biology has refined our understanding about ethylene receptor function and down-stream signal transduction components and has provided links between events at the molecular level with those at the organ level.  In particular, there appear to be two phases to the ethylene response which can be genetically and pharmacologically distinguished. The second, slower phase response to ethylene is dependent on the EIN3 and EIL1 transcription factors. In contrast, the events leading to the first phase response remain unknown. In collaboration with the lab of Steve Abel, we have mathematically modeled several network topologies to obtain a more refined understanding about how the pathway works and to make predictions about various pathway components (Prescott et al., 2016). We continue to uncover more details about the basis for the two phases of growth inhibition as well as develop more comprehensive network models to explain these properties. For more information refer to: Binder et al., 2004; Binder et al., 2004; Kim et al., 2011; Kim et al., 2012; Binder et al. 2018Park, 2023.

Growth responses in Arabidopsis
(click on image to link to time-lapse movies)

Seed germination during salt stress

Sub-functionalization of Ethylene Receptor Isoforms
A third area of current research is to determine the basis for ethylene receptor sub-functionalization (reviewed in Shakeel et al., 2013) . We have uncovered several instances where the receptors have become sub-functionalized. For instance, ETR1, ETR2, and EIN4 are required for normal growth recovery after removal of ethylene, while ERS1 and ERS2 are not. This function requires ETR1 histidine kinase activity (Binder et al., 2004). ETR1 plays the predominant role in mediating the inhibitory effects of silver ions on ethylene responses (McDaniel and Binder, 2012), in mediating many responses of roots to ethylene (Harkey et al., 2018) and in susceptibility to the cyst nematode Heterodera schactii (Piya et al., 2019). Interestingly, our research has also revealed instances of contrasting roles for certain receptor isoforms. The first instance that we found was that ETR1 is necessary and sufficient for ethylene-stimulated nutational bending (also called circumnutations) of Arabidopsis hypocotyls; by contrast loss of the other four receptor isoforms leads to constitutive nutations (Binder et al., 2006; Kim et al., 2011). Another instance of contrasting roles is that ETR1 (and to a lesser extent EIN4) inhibits and ETR2 stimulates seed germination during salt stress (Wilson et al., 2014a) and in darkness (Wilson et al., 2014b). The receiver domain of ETR1 has an important role during germination under salt stress. We've recently defined regions of the receiver domain important for specific traits (Bakshi et al., 2015). Thus, we have two instances where receptor isoforms have opposite roles in a trait. This is not explained by current models of ethylene signaling, but appears to involve crosstalk (see below).  We are now studying the mechanistic basis for these various roles.

Signaling Crosstalk and Non-Canonical Signaling
As part of our interest in receptor sub-functionalization, we are exploring signaling from the ethylene receptors that affects other hormone pathways (reviewed in Binder, 2020). For instance, there appears to be signaling from the ethylene receptors to components of the cytokinin pathway to modulate recovery kinetics (Binder et al. 2018) and susceptibility to the cyst nematode Heterodera schactii (Piya et al., 2019). This signaling is likely to involve phosphorelay from ETR1 to the cytokinin pathway. Interesting, some receptors seem to have ethylene-independent roles. For instance,  ETR1 and EIN4 stimulate, and ETR2 inhibits responses to abscisic acid during seed germination; these responses are independent of ethylene and the canonical ethylene signal transduction pathway  (Wilson et al., 2014a; Bakshi et al., 2018). Together, these projects are providing new information about the complex web of interactions important for plant survival.

Distribution of Putative Ethylene Receptors in Non-plant Species
(cyan- cyanobaceria, red- proteobacteria, yellow- other bacteria, purple- non-plant eukaryotes)

Ethylene Receptors in Non-plant Species
It is believed that plants acquired ethylene receptors during the endosymbiotic event that led to chloroplasts. It is still unknown which organism(s) initially evolved ethylene receptors. We are now studying putative ethylene receptors in various bacteria. We have shown that the cyanobacterium Synechocystis PCC 6803 contains a functional ethylene receptor (SynEtr1) that is involved in controlling various physiological processes such as phototaxis and biofilm formation. For instance, disruption of SynEtr1 leads to much faster phototaxis. This signaling pathway seems to have a role in modulating the extracellular surface of the bacterium. SynEtr1 also contains a phytochrome-like domain and has been shown to be a functional light receptor. Thus, SynEtr1 is a bifunctional receptor for both light and ethylene. We are now exploring the mechanism of ethylene signaling by SynEtr1 and characterizing putative ethylene receptors from other microbes. For more information refer to:  Rodriguez et al., 1999; Wang et al., 2006; Lacey and Binder, 2016Henry et al., 2017; Lacey et al. 2018; Papon and Binder, 2019; Allen et al. 2019 Bidon et al. 2020; and Carlew et al. 2020.

Funding for this research is largely provided by the National Science Foundation and USDA-NSF NIFA USDA-NIFA

Research Opportunities:
Interested in: studying signal transduction? Receptor-ligand interactions? Independent research? Working on a gas?
Contact me about research opportunities in my lab (Contact Dr. Binder).

We have built A Mobile Teaching Resource for Ethylene Kinetics (AMTREK) that can travel to science classrooms. Follow the link to find out more. Contact Dr. Binder if you want to arrange for this to be used by your students.

Some interesting, diverse, sometimes useful, and weird links:

And, now for something different...

Humor (or what passes for humor) and entertainment...

Last Updated
February  2023