title: NaStEP: a proteinase inhibitor essential to self-incompatibility and a positive regulator of HT-B stability in Nicotiana alata pollen tubes.
abstract: In Solanaceae, the self-incompatibility S-RNase and S-locus F-box interactions define self-pollen recognition and rejection in an S-specific manner. This interaction triggers a cascade of events involving other gene products unlinked to the S-locus that are crucial to the self-incompatibility response. To date, two essential pistil-modifier genes, 120K and High Top-Band (HT-B), have been identified in Nicotiana species. However, biochemistry and genetics indicate that additional modifier genes are required. We recently reported a Kunitz-type proteinase inhibitor, named NaStEP (for Nicotiana alata Stigma-Expressed Protein), that is highly expressed in the stigmas of self-incompatible Nicotiana species. Here, we report the proteinase inhibitor activity of NaStEP. NaStEP is taken up by both compatible and incompatible pollen tubes, but its suppression in Nicotiana spp. transgenic plants disrupts S-specific pollen rejection; therefore, NaStEP is a novel pistil-modifier gene. Furthermore, HT-B levels within the pollen tubes are reduced when NaStEP-suppressed pistils are pollinated with either compatible or incompatible pollen. In wild-type self-incompatible N. alata, in contrast, HT-B degradation occurs preferentially in compatible pollinations. Taken together, these data show that the presence of NaStEP is required for the stability of HT-B inside pollen tubes during the rejection response, but the underlying mechanism is currently unknown.
authors.affiliation: Departamento de Bioquímica, Facultad de Química, Universidad Nacional Autónoma de México, Mexico City DF 04510, Mexico.
authors.forename: Karina
authors.initials: K
authors.lastname: Jiménez-Durán
authors.forename: Bruce
authors.initials: B
authors.lastname: McClure
authors.forename: Florencia
authors.initials: F
authors.lastname: García-Campusano
authors.forename: Rogelio
authors.initials: R
authors.lastname: Rodríguez-Sotres
authors.forename: Jesús
authors.initials: J
authors.lastname: Cisneros
authors.forename: Grethel
authors.initials: G
authors.lastname: Busot
authors.forename: Felipe
authors.initials: F
authors.lastname: Cruz-García
mesh_terms: D000595:Amino Acid Sequence; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism*; D017343:Genes, Plant; D008969:Molecular Sequence Data; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D010936:Plant Extracts / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D053205:Pollen Tube / Q000235:genetics / Q000378:metabolism*; D054817:Pollination; D025941:Protein Interaction Mapping; D055550:Protein Stability; D017433:Protein Structure, Secondary; D059748:Proteolysis; D034622:RNA Interference; D060436:Self-Incompatibility in Flowering Plants; D020860:Subtilisin / Q000037:antagonists & inhibitors; D014026:Nicotiana / Q000235:genetics / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; C400763:HT protein, Nicotiana alata; C053865:Kunitz-type protease inhibitor, plant; D010455:Peptides; D010936:Plant Extracts; D010940:Plant Proteins; D020860:Subtilisin