Target deletion of the AAA ATPase PpCDC48II in Physcomitrella patens results in freezing sensitivity after cold acclimation

CDC48 is a highly conserved protein in eukaryotes and belongs to the AAA (ATPase associated with a variety of cellular activities) superfamily. It can interact with many different co-factors and form protein complexes that play important roles in various cellular processes. According to the Physcomitrella patens database, one member of the ATPases, the cell cycle gene PpCDC48II, was cloned. PpCDC48II contains two typical ATPase modules and is highly homologous to AtCDC48A. PpCDC48II was up-regulated in mRNA levels after incubation at 0A degrees C for 36 and 72 h. To further elucidate protein function, we disrupted the PpCDC48II gene by transforming P. patens with the corresponding linear genomic sequences. When treated to the same freezing stress, it was found that PpCDC48II knockout plants were less resistant to freezing treatment than wild type after acclimation. This suggested that PpCDC48II was an essential gene for low-temperature-induced freezing tolerance in P. patens cells.