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Abstract Detail


Protein Modification and Turnover

Hua, Zhihua [1], Meng, Xiaoying [2], Kao, Teh-hui [3].

Biochemical and Functional Studies of S-RNase-Mediated Self-incompatibility in Petunia inflata.

In Petunia inflata, two polymorphic genes at the S-locus, pistil-specific S-RNase and pollen-specific PiSLF, control the specificity of self-incompatibility (SI). A current hypothesis for the SI mechanism is that a PiSLF mediates specific degradation of its non-self S-RNases (products of other S-alleles), but allows its self S-RNase (product of its own S-allele) to degrade RNAs to result in growth inhibition of self-pollen tubes. To test this hypothesis, we have shown that (1) PiSLF is in a novel E3 ligase complex containing PiCUL1-G (a cullin) and PiSBP1 (a RING-HC protein); (2) PiSBP1 interacts with both PiSLFs and S-RNases; (3) a PiSLF interacts with its non-self S-RNases more strongly than with its self S-RNase in vitro; (4) S-RNases are degraded in pollen-tube extracts via the ubiquitin-26S proteasome pathway, albeit not in an S-dependent manner. We propose that PiSBP1 also acts as a mono-subunit E3 ligase that is responsible for basal degradation of all S-RNases, and that the PiSLF/PiCUL1-G/PiSBP1 complex preferentially interacts with non-self S-RNases to result in their ubiquitination and degradation. To further examine the interactions between PiSLF and S-RNases, we have expanded our study to include 6 S-linked pollen-expressed PiSLF-like genes whose deduced amino-acid sequences are 50 and 55% identical to that of PiSLF. We have (1) shown that none of them interact with S-RNases to any significant extent in vitro; (2) introduced two of these PiSLF-like genes, PiSLFLb-S2 and PiSLFLc-S1, into transgenic plants and shown that neither functions in SI; (3) identified three PiSLF-specific regions, not present in any of the 6 PiSLF-like proteins. The roles of these regions in differential interactions with self and non-self S-RNases are being examined.


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1 - The Pennsylvania State University, Intercollege Graduate Degree Program in Plant Biology, 403 Althouse Lab, University Park, PA, 16802, USA
2 - The Pennsylvania State University, Intercollege Graduate Degree Program in Plant Biology
3 - The Pennsylvania State University, Department of Biochemistry and Molecular Biology

Keywords:
self-incompatibility
protein-protein interaction
protein degradation
ubiquitination
SLF like gene.

Presentation Type: ASPB Minisymposium
Session: M22
Location: International Ballroom South/Hilton
Date: Wednesday, July 11th, 2007
Time: 8:30 AM
Number: M22001
Abstract ID:701


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