Chemical defenses are a major mechanism by which organisms interact with their environment, increasing community complexity by allowing many prey to co-occur with predators. In particular, chemical defenses commonly provide protection from predators for marine sponges and algae, as well as plants and insects found in freshwater environments. An important mystery regards the identity of chemoreceptors used by predators to detect chemical defenses and avoid noxious prey. In previous work, McCarty & Kubanek discovered a small protein expressed in the heads of various fish species that appears to explain why sponge chemical defenses are rejected by these fish when placed in their food. The first goal of this work is to determine how this protein, named RL-TGR, functions. The second goal is to determine whether other proteins, like RL-TGR, are involved in chemical sensing of other chemical defenses in aquatic environments. These studies will enable a new level of understanding of how predators and prey interact in the marine environment. This program includes educational opportunities for multiple undergraduates and graduate students, as well as an exploration program for high school students in association with the Georgia Aquarium in Atlanta.

The "RL-TGR" co-receptor is related to vertebrate RAMP proteins and thereby both the trafficking of this protein to cell membranes and its subsequent function require co-expression of a G-protein coupled receptor (GPCR) - however, the determinants of RL-TGR function have yet to be identified. Objectives of the collaborative project include the following: 1) Determine the mechanism of action of RL-TGR in chemoreception. Both zebrafish (a model organism) and bluehead wrasse (a marine generalist predator) respond to the presence of sponge-derived deterrent compounds laced into their food. The anatomical distribution of RL-TGR will be mapped in zebrafish and bluehead wrasse using both gene and protein expression approaches. Which portions of RL-TGR modulate responses to chemical defenses will be determined using mutagenesis, electrophysiological assays, and co-expression with GPCRs. The endogenous GPCR(s) that physically and functionally couple with RL-TGR to enable chemoreception by fish will be identified, including via mass spectrometric proteomics. 2) Explore the breadth of RL-TGR signaling and terpene glycoside-based chemical defense. The diversity and evolution of RL-TGR-like co-receptors in animals will be explored using bioinformatic approaches. We will compare RL-TGR-mediated binding and physiological responses to various chemical defense ligands from diverse prey in expression studies using RL-TGR orthologs from model fish species. These studies will apply new knowledge about the mechanism of RL-TGR signaling to enable an understanding of the breadth of RL-TGR function in chemical defense chemoreception.

Agency
National Science Foundation (NSF)
Institute
Division of Integrative Organismal Systems (IOS)
Type
Standard Grant (Standard)
Application #
1354837
Program Officer
Irwin Forseth
Project Start
Project End
Budget Start
2014-08-01
Budget End
2019-07-31
Support Year
Fiscal Year
2013
Total Cost
$629,447
Indirect Cost
Name
Georgia Tech Research Corporation
Department
Type
DUNS #
City
Atlanta
State
GA
Country
United States
Zip Code
30332