Hsp40s or DnaJ/J-proteins are evolutionarily conserved in all organisms as co-chaperones of molecular chaperone HSP70s that mainly participate in maintaining cellular protein homeostasis, such as protein folding, assembly, stabilization, and translocation under normal conditions as well as refolding and degradation under environmental stresses. It has been reported that Arabidopsis J-proteins are classified into four classes (types A-D) according to domain organization, but their phylogenetic relationships are unknown. Here, we identified 129 J-proteins in the world-wide popular vegetable Brassica oleracea, a close relative of the model plant Arabidopsis, and also revised the information of Arabidopsis J-proteins based on the latest online bioresources. According to phylogenetic analysis with domain organization and gene structure as references, the J-proteins from Arabidopsis and B. oleracea were classified into 15 main clades (I-XV) separated by a number of undefined small branches with remote relationship. Based on the number of members, they respectively belong to multigene clades, oligo-gene clades, and mono-gene clades. The J-protein genes from different clades may function together or separately to constitute a complicated regulatory network. This study provides a constructive viewpoint for J-protein classification and an informative platform for further functional dissection and resistant genes discovery related to genetic improvement of crop plants.

Background: Dendrobium catenatum is a kind of precious Traditional Chinese Medicine, and possesses unique developmental programs and epiphytic lifestyle. Histone acetyltransferases (HATs) and histone deacetylases (HDACs) are responsible for maintenance of histone acetylation homeostasis, and they are widely involved in developmental regulation and stress responses via remodeling chromatin structure, but their biological functions in orchid plants remain largely unknown.Results: Here we identified 8 HAT genes and 14 HDAC genes from D. catenatum genome. We carried out phylogenetic construction, gene structure and domain architecture analysis of these D. catenatum HAT/HDAC (DcHAT/DcHDAC) proteins using the well-defined homologs from the model plants Arabidopsis thaliana and Oryza sativa as references. DcHAT proteins can be classified into four families: GNAT family (3 members), MYST family (2), CBP family (2), and TAFII250 family (1), and DcHDAC proteins can be grouped into three families: RPD3/HDA1 family (10), SIR2 family (2), and HD2 family (2), in accordance with previously described classification. Cis-acting element analysis indicated that the promoter regions of DcHAT/DcHDAC genes contain diverse stress-responsive elements. Subcellular localization predictions suggested that DcHAT/DcHDAC proteins might be localized in nucleus or/and cytoplasm. Spatiotemporal expression profiling showed that DcHAT/DcHDAC genes generally exhibit either universal or specific expression pattern in different tissues and organs. Finally, stress response assay suggested drought treatment significantly represses the expression of DcHAG1 and DcHDA14, cold exposure evidently influences the expression of DcHAG1 and DcHDT1, and heat shock has a broad impact on the expression of DcHAT/DcHDAC genes.Conclusions: In this study, we reveal the identification and expression profiles of DcHATs and DcHDACs in epiphytic orchid plant D. catenatum, indicating their roles in the regulation of both long-term developmental programs and short-term stress responses. This study provides a foundation for in-depth functional excavation of HATs/HDACs associated with dynamic histone acetylation levels in orchids.