Identification of subfunctionalized aggregate-remodeling J-domain proteins in plants
Hsp70s and J-domain proteins (JDPs) are among the most critical components of the cellular protein quality control machinery, playing crucial roles in preventing and solubilizing cytotoxic protein aggregates. Bacteria, yeast and plants additionally have large, multimeric Hsp100-class disaggregases which, allow the resolubilization of otherwise "dead-end" aggregates, including amyloids. JDPs interact with aggregated proteins and specify the aggregate remodeling activities of Hsp70s and Hsp100s. Plants have a complex network of cytosolic Hsp70s and JDPs, however the aggregate remodeling properties of plant JDPs are not well understood. Here we identify evolutionary-conserved Class II JDPs in the model plant Arabidopsis thaliana with distinct aggregate remodeling functionalities. We identify eight plant orthologs of the yeast protein, Sis1, the principal JDP responsible for directing the yeast chaperone machinery for remodeling protein aggregates. Expression patterns vary dramatically among the eight paralogous proteins under a variety of stress conditions, indicating their subfunctionalization to address distinct stressors. Consistent with a role in solubilizing cytotoxic protein aggregates, six of these plant JDPs associate with heat-induced protein aggregates in vivo as well as colocalize with plant Hsp101 to distinct heat-induced protein aggregate centers. Finally, we show that these six JDPs can differentially remodel multiple model protein aggregates in yeast confirming their involvement in aggregate resolubilization. These results demonstrate that compared to complex metazoans, plants have a robust network of JDPs involved in aggregate remodeling activities with the capacity to process a variety of protein aggregate conformers.