Bryan Hau MSc, Snedden Lab Investigating the interaction of Arabidopsis calmodulin-like (CML) proteins with calmodulin-binding transcription activators (CAMTAs) Understanding the how organisms detect and interpret information from their environment is an ongoing goal in cell biology. A common theme among eukaryotic cells is the use of calcium ions (Ca2+) as second messengers during information processing. In plants, Ca2+ signals are evoked during responses to abiotic and biotic stresses and during development. These signals are detected by Ca2+-binding proteins (sensors), such as the evolutionarily-conserved protein calmodulin (CaM), which regulates various downstream target proteins to organize signal transduction pathways. In addition to CaM, plants have evolved a remarkable array of CaM-like proteins (CMLs) that are not found in animals. The genetic model, Arabidopsis, has seven CaMs and 50 CMLs, most of which remain unstudied. Why do plants need so many of these Ca2+ sensors? What are their downstream targets? How do they contribute to Ca2+ signaling during stimulus response? Research on CML structure/function is needed to develop a broader understanding of how plants respond to environmental cues. Recently, our lab has been exploring the roles of two paralogs, CML13,14, which possess unique biochemical properties among CaMs and CMLs. To help uncover CML13,14 function, we screened a yeast 2-hybrid library for putative target proteins and discovered 3 families of functionally unrelated proteins that share a common structural feature; tandem IQ domains. IQs are unique CaM binding domains that have been mainly studied in the myosin motor proteins of animals. In addition to myosins, we identified several CaM-binding transcription activators (CAMTAs) as putative CML13,14 targets. CAMTAs possess multiple IQ domains and are important transcription factors in plants that regulate gene expression during abiotic and biotic stresses such as cold, drought, salt stress, pathogen attack, and herbivory. I will present data from my MSc project where I explored the question; are Arabidopsis CAMTAs targets of CML13,14? My project focused mainly on assessing the properties of CML13/14-CAMTA binding, using both in planta and in vitro methods. Using a genetic approach, I also discovered a key role in salinity stress response for CML13. Collectively, my data supports the hypothesis that CAMTAs and CMLs interact in plants and suggests a novel mechanism through which Ca2+ signals regulate gene expression during stress response.
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