Genome-wide identification, characterization and expression analysis of the Bcl-2 associated athanogene (BAG) gene family in Physcomitrium patens

The Bcl-2-associated athanogene (BAG) family is an evolutionarily conserved, multifunctional group of co-chaperones regulators that modulate a number of diverse processes. Plant BAG genes were identified to play an extensive role in processes of programmed cell death (PCD) ranging from growth and development to stress responses. In this study, we identified BAG genes from different photosynthetic organisms in order to gather evolutionary insights on these proteins followed by an in silico characterization of the BAG family in the bryophyte Physcomitrium patens. Ten putative PpBAGs harbouring a characteristic BAG domain were grouped into two subfamilies based on the presence of additional conserved domains and phylogenetic distances. Group I consisted of PpBAG4 and PpBAG5, containing an additional ubiquitin-like domain, and PpBAG10 with only the BAG domain. Group II consisted of PpBAG1-3 and PpBAG6-9, containing a calmodulin-binding IQ motif, a novel feature associated with plant BAG proteins. Interestingly, PpBAG9 exhibits an EF-Hand domain, not reported to date in this class of proteins. Caspase cleavage sites in PpBAG1, PpBAG3, PpBAG4-5 and PpBAG9 were predicted. In silico analysis of BAG genes revealed the presence of stress responsive elements, and a stress-regulated expression pattern which appears to be dependent on specifically organized promoter regulatory elements. According to our analyses, the present data suggest that some members of P. patens BAG gene family may play a role in heat responses, autophagy and pathogen immunity. Further studies are required to unveil the role of specific members of this gene family in PCD and stress responses in P. patens. Key messageGenome-wide identification and phylogenetic relationships combined with in silico gene-expression profiling and protein-interaction analysis of PpBAGs in Physcomitrium patens, highlight the importance of a particular set in stress tolerance.