title: Identification of major lysine residues of S(3)-RNase of Petunia inflata involved in ubiquitin-26S proteasome-mediated degradation in vitro.
abstract: S-RNase-based self-incompatibility has been identified in three flowering plant families, including the Solanaceae, and this self/non-self recognition mechanism between pollen and pistil is controlled by two polymorphic genes at the S-locus, S-RNase and S-locus F-box (SLF). S-RNase is produced in the pistil and taken up by pollen tubes in a non-S-haplotype-specific manner. How an allelic product of SLF interacts with self and non-self S-RNases to result in growth inhibition of self pollen tubes is not completely understood. One model predicts that SLF targets non-self S-RNases for ubiquitin/26S proteasome-mediated degradation, thereby only allowing self S-RNase to exert cytotoxic activity inside a pollen tube. To test this model, we studied whether any of the 20 lysine residues in S(3)-RNase of Petunia inflata might be targets for ubiquitination. We identified six lysines near the C-terminus for which mutation to arginine significantly reduced ubiquitination and degradation of the mutant S(3)-RNase, GST:S(3)-RNase (K141-164R) in pollen tube extracts. We further showed that GST:S(3)-RNase (K141-164R) and GST:S(3)-RNase had similar RNase activity, suggesting that their degradation was probably not caused by an ER-associated protein degradation pathway that removes mis-folded proteins. Finally, we showed that PiSBP1 (P. inflata S-RNase binding protein 1), a potential RING-HC subunit of the PiSLF (P. inflata SLF)-containing E3-like complex, could target S-RNase for ubiquitination in vitro. All these results suggest that ubiquitin/26S proteasome-dependent degradation of S-RNase may be an integral part of the S-RNase-based self-incompatibility mechanism.
authors.affiliation: Intercollege Graduate Degree Program in Plant Biology, The Pennsylvania State University, University Park, PA 16802, USA.
authors.forename: Zhihua
authors.initials: Z
authors.lastname: Hua
authors.forename: Teh-Hui
authors.initials: TH
authors.lastname: Kao
mesh_terms: D000595:Amino Acid Sequence; D018506:Gene Expression Regulation, Plant; D008239:Lysine / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D032306:Petunia / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D053205:Pollen Tube / Q000201:enzymology / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012260:Ribonucleases / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D010940:Plant Proteins; D011994:Recombinant Proteins; D025801:Ubiquitin; D012260:Ribonucleases; C022542:ribonuclease S; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; D008239:Lysine