title: A novel aspartic proteinase is targeted to the secretory pathway and to the vacuole in the moss Physcomitrella patens.
abstract: In seed plants aspartic proteases (APs) are known to reside in storage vacuoles. Targeting to this compartment is provoked by a secretory signal peptide and the plant-specific insert (PSI). In order to study secretory and vacuolar targeting in a seedless plant, the moss Physcomitrella patens, we isolated a cDNA encoding PpAP1, a novel aspartic proteinase. Sequence alignment with other members of the family of plant APs (EC 3.4.23) revealed a high overall identity and the Pfam motifs for aspartic proteinase and PSI were clearly recognised. In phylogenetic analysis PpAP1 was placed at a very basal position outside of the bigger clusters. Protoplasts transiently expressing the PpAP1 signal peptide fused to GFP showed fluorescence in a well-developed ER-Golgi network. A C-terminal fusion of GFP to the entire PpAP1 protein showed vacuolar fluorescence in transiently transfected protoplasts. Therefore, the vacuole is apparently the in-vivo target for PpAP1. In this study the three-dimensional peculiarity of the endomembrane continuum of ER and Golgi was visualised in a seedless plant for the first time. Above all the functionality of the secretory and the vacuolar targeting signals make them become useful tools for biotechnological approaches.
authors.affiliation: Plant Biotechnology, University of Freiburg, Freiburg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Schaaf
authors.forename: Ralf
authors.initials: R
authors.lastname: Reski
authors.forename: Eva L
authors.initials: EL
authors.lastname: Decker
mesh_terms: D000595:Amino Acid Sequence; D016282:Aspartic Acid Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019068:Bryopsida / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D007425:Intracellular Membranes / Q000378:metabolism; D008969:Molecular Sequence Data; D010802:Phylogeny; D021382:Protein Sorting Signals / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D022142:Secretory Vesicles / Q000378:metabolism*; D016415:Sequence Alignment; D020539:Sequence Analysis, Protein; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D021382:Protein Sorting Signals; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D016282:Aspartic Acid Endopeptidases