Analyses of the Signaling Pathway in Light Induced Phosphorylation of the H ATPase in Thalli Previous studies have shown that a potent protein kinase inhibitor, K 252a, and a type 1 2A protein phosphatase inhibitor, calyculin A , inhibit blue light induced phosphorylation activation of the plasma membrane H ATPase in stomatal guard cells . We tested the effects of K 252a and CA on light induced phosphorylation of the H ATPase in thalli and found that both K 252a at 10 mM and CA at 0.5 mM severely inhibited phosphorylation . In contrast, K 252a and CA had no effect on the FC induced phosphorylation of the H ATPase , suggesting that a K 252a sensitive protein kinase and CA sensitive protein phosphatase are involved in the signaling pathway of the light induced phosphorylation of the H ATPase in thalli and that a K 252a insensitive protein kinase catalyzes direct phosphorylation of the H ATPase in response to FC. This result is consistent with previous reports showing that direct phosphorylation of the penultimate Thr in H ATPase is mediated by a K 252a insensitive protein kinase . DISCUSSION The Plasma Membrane H ATPase in M. polymorpha It has been demonstrated that the H ATPase is essential for vascular plants .
Accordingly, ATP-competitive JAK inhibitor treatment with the H ATPase inhibitors erythrosine B and vanadate severely inhibited the growth of thalli in the liverwort M. polymorpha , suggesting a critical role of the H ATPase in growth and development in M. polymorpha. However, there has not been any study on the plasma membrane H ATPase in M. polymorpha. In addition, despite detailed characterization of the pT H ATPase in vascular plants, the emergence and evolution of the pT H ATPase remain unknown. In this study, we showed that the liverwort M. polymorpha, which represents the most basal lineage of extant land plants, possesses both the pT H ATPase genes , which contain the characteristic penultimate Thr in the C terminus, and the non pT H ATPase genes . These results strongly suggest that the pT H ATPases most likely did exist in the last common ancestor of liverworts. As liverworts represent the most basal lineage of extant land plants, our data suggest that plants had already acquired pT H ATPase when they emerged on the terrestrial environment.
It should be noted that MpHA6 possesses regions R I and R II, which are important for autoinhibitory effects Silodosin on the H ATPase, and YTF in the position of YTV in the pT H ATPase. MpHA6, therefore, may be a transition form in the evolution to the pT H ATPase, because a simple truncation of this gene could create a pT H ATPase. A whole genome sequence has revealed that one of the most basal of vascular plant lycophytes, S. moellendorffii, most likely possesses only the pT H ATPase . In contrast, the bryophyte M. polymorpha possesses both types of H ATPase .