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Plant J. 2014 Jun;78(6):1014-21. doi: 10.1111/tpj.12528. Epub 2014 May 21.

Ubiquitin-proteasome-mediated degradation of S-RNase in a solanaceous cross-compatibility reaction.

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Graduate School of Biological Sciences, Nara Institute of Science and Technology, 8916-5 Takayama, Ikoma, Nara, 630-0192, Japan.


Many plants have a self-incompatibility (SI) system in which the rejection of self-pollen is determined by multiple haplotypes at a single locus, termed S. In the Solanaceae, each haplotype encodes a single ribonuclease (S-RNase) and multiple S-locus F-box proteins (SLFs), which function as the pistil and pollen SI determinants, respectively. S-RNase is cytotoxic to self-pollen, whereas SLFs are thought to collaboratively recognize non-self S-RNases in cross-pollen and detoxify them via the ubiquitination pathway. However, the actual mechanism of detoxification remains unknown. Here we isolate the components of a SCF(SLF) (SCF = SKP1-CUL1-F-box-RBX1) from Petunia pollen. The SCF(SLF) polyubiquitinates a subset of non-self S-RNases in vitro. The polyubiquitinated S-RNases are degraded in the pollen extract, which is attenuated by a proteasome inhibitor. Our findings suggest that multiple SCF(SLF) complexes in cross-pollen polyubiquitinate non-self S-RNases, resulting in their degradation by the proteasome.


26S proteasome; Petunia hybrida; SCF SLF; Solanaceae; self-/non-self discrimination; self-incompatibility; ubiquitination

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