Postdoc Michigan State University east lansing, Michigan
Body of Abstract: Evolution and diversification of the ACT-like domain associated with plant basic helix–loop–helix transcription factors
Yun Sun Leea, Shin-Han Shiub,c, Erich Grotewolda* aDepartment of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48823 bDepartment of Plant Biology, Michigan State University, East Lansing, MI 48824 cDepartment of Computational Mathematics, Science, and Engineering, Michigan State University, East Lansing, MI 48824 *Corresponding author
Basic helix–loop–helix (bHLH) proteins are one of the largest families of transcription factor (TF) in eukaryotes, and ~30% of all flowering plants’ bHLH TFs contain the aspartate kinase, chorismate mutase, and TyrA (ACT)-like domain at variable distances C-terminal from the bHLH. However, the evolutionary history and functional consequences of the bHLH/ACT-like domain association remain unknown. Here, we show that this domain association is unique to the plantae kingdom with chlorophytes harboring a small number of bHLH genes with a variable frequency of ACT-like domain’s presence. bHLH-associated ACT-like domains form a monophyletic group, indicating a common origin. Indeed, phylogenetic analysis results suggest that the association of ACT-like and bHLH domains occurred early in Plantae by recruitment of an ACT-like domain in a common ancestor with widely distributed ACT DOMAIN REPEAT (ACR) genes by an ancestral bHLH gene. We determined the functional significance of this association by showing that Chlamydomonas reinhardtii ACT-like domains mediate homodimer formation and negatively affect DNA binding of the associated bHLH domains. We show that, while ACT-like domains have experienced faster selection than the associated bHLH domain, their rates of evolution are strongly and positively correlated, suggesting that the evolution of the ACT-like domains was constrained by the bHLH domains. This study proposes an evolutionary trajectory for the association of ACT-like and bHLH domains with the experimental characterization of the functional consequence in the regulation of plant-specific processes, highlighting the impacts of functional domain coevolution.