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.