Evolutionary appearance of the plasma membrane H (+) -ATPase containing a penultimate threonine in the bryophyte.

The plasma membrane H (+) -ATPase provides the driving force for solute transport via an electrochemical gradient of H (+) across the plasma membrane, and regulates pH homeostasis and membrane potential in plant cells. However, the plasma membrane H (+) -ATPase in non-vascular plant bryophyte is largely unknown. Here, we show that the moss Physcomitrella patens, which is known as a model bryophyte, expresses both the penultimate Thr-containing H (+) -ATPase (pT H (+) -ATPase) and non-pT H (+) -ATPase as in the green algae, and that pT H (+) -ATPase is regulated by phosphorylation of its penultimate Thr. A search in the P. patens genome database revealed seven H (+) -ATPase genes, designated PpHA (Physcomitrella patens H (+) -ATPase). Six isoforms are the pT H (+) -ATPase; a remaining isoform is non-pT H (+) -ATPase. An apparent 95-kD protein was recognized by anti-H (+) -ATPase antibodies against an isoform of Arabidopsis thaliana and was phosphorylated on the penultimate Thr in response to a fungal toxin fusicoccin and light in protonemata, indicating that the 95-kD protein contains pT H (+) -ATPase. Furthermore, we could not detect the pT H (+) -ATPase in the charophyte alga Chara braunii, which is the closest relative of the land plants, by immunological methods. These results strongly suggest the pT H (+) -ATPase most likely appeared for the first time in bryophyte.