Identification of cystosolic Mg2+-dependent soluble inorganic pyrophosphatases in potato and phylogenetic analysis

Using polyclonal antibodies raised against a previously cloned potato Mg2+- dependent soluble inorganic pyrophosphatase (ppa1 gene) [8], a second gene, called ppa2, could be isolated. A single locus homologous to ppa2 was mapp ed on potato chromosomes, unlinked to the two loci identified for ppa1. Fro m a phylogenetic and structural point of view, the PPA1 and PPA2 polypeptid es are more closely related to prokaryotic than to eukaryotic Mg2+-dependen t soluble inorganic pyrophosphatases (soluble PPases). Subcellular localiza tion by immunogold electron microscopy, using sections from leaf parenchyma cells, showed that PPA1 and PPA2 are localized to the cytosol. Based on th ese observations, the likely phylogenetic origin and the physiological sign ificance of the cytosolic soluble pyrophosphatases are discussed.