Auxin response factors (ARF) are transcriptional regulators for growth and development in a breadth of plants including food and fuel crops. Within even a single species, the regulatory mechanism is complicated by the multiplicity of highly homologous proteins. In addition, co-occurrence and co-localization of ARF transcription activators and repressors appear necessary to differentiate developmental stages. The passive repression provided by ARF transcription repressors is complemented by active repression and hormonal regulation through interaction with the Aux/IAA proteins. These regulatory events are proposed to occur primarily through the interaction of their C-terminal Phox and Bem1 (PB1) domains. All PB1 domains in this family include two oppositely-charged faces to create complementary sites for protein-protein binding through ionic interactions. Depending on the specificity and oligomeric state of these interactions, homo- and heterodimerization as well as homo- and hetero-oligomerization appear feasible as well as consequential. This work directly compares activating ARF PB1 domains and a repressing ARF PB1 domain to further understand the interplay in regulation. We applied endogenous and exogenous fluorescence lifetime experiments with size exclusion chromatography to deconstruct intra- from intermolecular changes in the shift from monomer through oligomer. Specifically, both ARF repressing PB1 domains and activating PB1 domains demonstrate heterodimerization and oligomerization, but the extent of oligomerization as well as the cooperativity between the two faces of the PB1 domains varies. These results have significant implications for the proposed oligomeric states in vivo. As PB1 domains are found across eukaryotes, this work holds significant promise for to better understand the diversity in this family of important interaction domains.

Direct comparison of paralogous PB1 domains with disparate roles in regulation

2019 Spring National Meeting

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.