Arabidopsis atDjC53 encoding a type III J-protein plays a negative role in heat shock tolerance

摘要

J-proteins have been considered as obligate chaperones with Hsp70 in prokaryotes as well as eukaryotes. We have cloned and characterized a novel gene, atDjC53 (A rabidopsis t haliana DnaJ type C protein 53), encoding a type III J-class protein, the function of which has not yet been identified. Deduced amino acid sequences of atDjC53 show the highest homology (72 %) with J-proteins from Glycine max, Populus trichocarpa, and Ricnus communis and with the A. thaliana type III J-class protein, atDjC31 (53 %). Based on the real-time quantitative RT-PCR analysis, the mRNA levels of atDjC53 were increased in response to heat shock (HS) stress, suggesting its function in the HS tolerance signaling response. Subcellular localization studies demonstrated that the atDjC53-GFP fusion protein was localized in the nucleus. Differential RNA expression of atDjC53 by HS stresses inspired us to test the HS tolerance of atDjC53 in Arabidopsis. At the seed germination and mature plant stages, overexpression of atDjC53 in Arabidopsis reduced thermotolerance compared to the wild-type. In the 35S:atDjC53 transgenic plants, RNA expression levels of several HS-responsive genes including Hsp25.3-P and Hsa32 were significantly reduced compared to that of the WT during the recovery period after HS. Thermotolerance test indicated that ectopic expression of atDjC53 clearly attenuated the HS tolerance of Arabidopsis possibly due to the reduced expression levels of several key Hsp genes as compared to those observed in the WT plants. These results suggested that atDjC53 may play a negative regulatory role in response to HS.