Identification of subfunctionalized aggregate-remodeling J-domain proteins in Arabidopsis thaliana.

J-domain proteins (JDPs) are critical components of the cellular protein quality control machinery, playing crucial roles in preventing the formation and, solubilization of cytotoxic protein aggregates. Bacteria, yeast, and plants additionally have large, multimeric heat shock protein 100 (Hsp100)-class disaggregases that resolubilize protein aggregates. JDPs interact with aggregated proteins and specify the aggregate-remodeling activities of Hsp70s and Hsp100s. However, the aggregate-remodeling properties of plant JDPs are not well understood. Here we identify eight orthologs of Sis1 (an evolutionarily conserved Class II JDP of budding yeast) in Arabidopsis thaliana with distinct aggregate-remodeling functionalities. Six of these JDPs associate with heat-induced protein aggregates in vivo and co-localize with Hsp101 at heat-induced protein aggregate centers. Consistent with a role in solubilizing cytotoxic protein aggregates, an atDjB3 mutant had defects in both solubilizing heat-induced aggregates and acquired thermotolerance as compared with wild-type seedlings. Next, we used yeast prions as protein aggregate models to show that the six JDPs have distinct aggregate-remodeling properties. Results presented in this study, as well as findings from phylogenetic analysis, demonstrate that plants harbor multiple, evolutionarily conserved JDPs with capacity to process a variety of protein aggregate conformers induced by heat and other stressors.