A direct phosphorylation screening of a rice cDNA library resulted in isolation of 35 BIP clones encoding brassinosteroid receptor kinase (BRI1)-interacting proteins. Among the candidate substrates for BRI1, two clones were found to encode similar proton pump interactor proteins homologous to Arabidopsis PPI1, which was reported to interact with a regulatory region of plasma membrane H+-ATPase. The rice proton pump interactors BIP103 and BIP131 contained 627 and 621 amino acids, respectively, with carboxyl-terminal hydrophobic region characteristic of tail-anchored proteins. Northern blotting analysis indicated that mRNAs for both interactors increased significantly after brassinolide treatment of lamina joint cells, which are especially sensitive to exogenous brassinosteroids.
ASJC Scopus subject areas