Pattern di espressione del gene Ppi1 e analisi di mutanti ppi1 e ppi 2 in Arabidopsis thaliana

The proton pump interactor (Ppi) gene family of Arabidopsis thaliana: expression pattern of Ppi1 and characterisation of knockout mutants for Ppi1 and 2. Plant plasma membrane H+-ATPases (PM H+-ATPase) are essential for establishing a proton electrochemical gradient across the cell plasma membrane. Their regulation is poorly understood, except for the role of 14-3-3 proteins, which relieve autoinhibition from the C-terminal domain. A novel protein interacting with this domain was recently identified in Arabidopsis and named PPI1 (Proton Pump Interactor 1). PPI1 stimulates PM H+-ATPase activity in vitro. Here, we analyse the expression pattern of Ppi1 using b-glucuronidase as a reporter. Expression is strong in root and shoot vascular systems, particularly in meristematic and sink tissues, as well as in pollen, stigmas and siliques, but not in developing embryos. Removal of the first intron decreased GUS expression 45-fold. We also analysed the transcription of Ppi2, another gene in the family, and demonstrated that Ppi2 is expressed in seedlings, cultured cells and flowers. Insertional mutants for both Ppi1 and Ppi2 were isolated. Two different mutants of Ppi1 showed aberrant mRNAs and lacked any detectable protein and are therefore true knockouts. At the plant level, neither of the single mutants nor the double ppi1ppi2 mutant showed an altered phenotype in standard growth conditions under acid load or salt stress.