Binder Lab
est. 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. Work 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 molecular modeling, and genetics to unravel the complexities of ethylene signaling. There are several aspects of ethylene signaling we are actively pursuing right now.

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 while 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. However, more recent research in the lab suggests there may actually be a second metal-binding site in some, but not all, of the receptor isoforms. Future work is geared towards testing this. Another chemical approach we have used is to analyze ethylene binding and receptor function in the presence of various strained alkenes. Finally, we have used alanine-scanning 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. We are currently expanding this to include other techniques of analysis to determine conformational changes that occur in the binding domain during ethylene binding and transduction. For more information refer to: Rodriguez et al., 1999; Wang et al., 2006; Pirrung et al., 2008; Binder et al., 2010; McDaniel and Binder, 2012.

Kinetics of Growth Inhibition
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 system has revealed transient and subtle changes due to ethylene that would have otherwise remained unknown. 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. Efforts continue to define the central roles for EIN3 and EIL1 and to uncover more details about the basis for the two phases of growth inhibition as well as develop 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. In collaboration with the lab of Steve Abel, we are computationally modeling some of these 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).


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

Seed germination during salt stress

Specific Roles for Ethylene Receptor Isoforms
A third area of current research is to determine the basis for ethylene receptor sub-functionalization. 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 is function requires ETR1 histidine kinase activity (Binder et al., 2004). We have also found that ethylene stimulates nutational bending of hypocotyls that are dependent on the ETR1 receptor. Nutations (also called circumnutations) are nodding or coiling movements and are thought to be important in allowing the roots and shoots to penetrate the soil. ETR1 is necessary and sufficient for this response, whereas loss of the other four receptor isoforms leads to constitutive nutations (Binder et al., 2006; Kim et al., 2011). Another instance of sub-functionalization is that ETR1 inhibits and ETR2 stimulates seed germination during salt stress (Wilson et al., 2014a) and in darkness (Wilson et al., 2014b). The receiver domain has an important role in this and 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. ETR1 also plays the predominant role in mediating the inhibitory effects of silver ions on ethylene responses (McDaniel and Binder, 2012). We are now studying the mechanistic basis for these various roles.

Signaling Crosstalk
We are also interested in how ethylene affects other signaling pathways to control various processes in plant growth and development. For instance, we found that auxin transport is involved in ethylene-stimulated nutations (Binder et al., 2006) suggesting that ETR1 may specifically affect auxin transport. Ethylene is regulating gibberellic acid levels or signaling to modulate growth inhibition and recovery kinetics (Kim et al., 2012). Interesting, some receptors seem to have ethylene-independent roles. For instance,  ETR1 stimulates and ETR2 inhibits responses to abscisic acid during seed germination in what appear to be ethylene-independent ways (Wilson et al., 2014a). We have also explored how other hormones affect ethylene signaling and made the surprising observation that lowered jasmonic acid levels results in certain ethylene-insensitive mutants becoming responsive to ethylene (Kim et al., 2013a). Similarly, the jasmonic acid insensitive coi1-37 mutants are somewhat more responsive to ethylene; in contrast, addition of jasmonic acid reduces responses to ethylene at higher ethylene levels (Kim et al., 2013b). Together, these projects are providing new information about the complex web of interactions important for plant survival.


Phototaxing Synechocystis Colonies
(chlorophyll fluorescence image)

Ethylene Receptors in Non-plant Species
It is believed that ethylene receptors were acquired during the endosymbiotic event that led to chloroplasts. We are now studying putative ethylene receptors in various bacteria. We have shown that the cyanobacterium Synechocystis contains a functional ethylene receptor (SynEtr1). It 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 Synechocystis. 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 bacterial species. For more information refer to:  Rodriguez et al., 1999; Wang et al., 2006; Lacey and Binder, 2016.

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, for something different...

Last Updated
August 2016