A genetic interaction between chaperone and proteasome activity in Arabidopsis

Organisms contain cellular mechanisms that help maintain the correct structure of proteins in order to ensure for their proper function. These include the activity of several families of protein chaperones called heat shock proteins (HSP) that aid in protein folding. If proteins are unable to be correctly folded they are degraded in an ubiquitin dependent manner by proteolytic protein complexes such as the 26S proteasome. BOBBER1 (BOB1) is the only known Arabidopsis small heat shock protein (sHSP) that is required for thermotolerance as well as for normal development. A partial loss of function allele of BOB1, bob1-3, exhibits pleiotropic developmental phenotypes including serrated leaves, delayed growth, and defects in thermotolerance. A strong allelic combination, bob1-3/bob1-1 (a null allele), results in much more severe phenotypes including abaxial leaf spurs, polarity defects in floral organs, and fasciated meristems. In order to identify developmental pathways that BOB1 functions in we performed an EMS modifier screen in a bob1-3 background. bom has bob1-3 dependent phenotypes and displays phenotypes similar to those observed in strong bob1-3/bob1-1 allelic combinations. We used next generation sequencing to simultaneously map and clone bom. BOM encodes the RPT2a AAA-ATPase subunit of 26S proteasome. Phenotypic analysis of rosette size, total above ground growth, and roots, of single and double mutant plants suggests that there is a complex genetic interaction between BOB1 and BOM. These data demonstrate a genetic link between protein folding and protein degradation and suggest that plants with reduced chaperone activity are sensitized to decreases in proteasome activity