Abstract
J-domain containing molecular chaperones (J proteins) are functional partners for Hsp70. Budding yeast has three J proteins in the ER: Scj1p and Jem1p functioning in the ER quality control, and Sec63p functioning in protein translocation across the ER membrane as partners for BiP, an Hsp70 in the ER. We found that Arabidopsis has homologs of these yeast ER J proteins, which we designated AtScj1A, AtScj1B, AtJem1, AtSec63A and AtSec63B. Analyses of deletion mutants of these J protein genes showed that only AtSEC63A is essential for the Arabidopsis growth. Although deletion mutants of each of the other ER J protein genes were viable, we found induction of the AtSCJ1A and the AtJEM1 genes in the atscj1b mutant and induction of the AtSCJ1A gene in the atjem1 mutant, suggesting the functional redundancy between these J proteins. We also found that the atscj1b mutants became sterile when they grew at high temperature.
