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IGDB Scientists Revealed a Major Physical Force between the Pollen S and Pistil S Interactions in Self-Incompatibility of Flowering Plants.
Self and non-self recognition and discrimination are crucial to the survival of all living organisms ranging from bacteria to humans. Self-incompatibility (SI) is one of the most important self/non-self discrimination system widely found in angiosperms and, in many species, is controlled by a single polymorphic S-locus. In the Solanaceae, Rosaceae and Plantaginaceae, the S-locus encodes a single S-RNase and a cluster of S-locus F-box (SLF) proteins to control the pistil and pollen expression of SI, respectively. Previous studies have shown that their cytosolic interactions determine their recognition specificity. In eukaryotes, it is known that several properties of protein-protein interfaces such as complementarities between protein surfaces, residue interface propensities, hydrophobicity and conformational changes, contribute to protein-protein interactions, but the physical force between the interactions of S-RNase and SLF remains unclear.
Researchers from Prof. XUE Yongbiao’s lab at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, revealed that the electrostatic potentials of SLF contribute to the pollen S specificity through a physical mechanism of “like charges repel and unlike charges attract” between SLFs and S-RNases in Petunia hybrida.  
They identified one major region each from SLFs and S-RNases involved in their physical interactions in P. hybrida, and found the relationships of surface electrostatic potentials of most pairs of SLF and S-RNase are consistent with their recognition specificity in vivo, indicating that the electrostatic potentials of SLF and S-RNase proteins could serve as a major basis for their physical interactions. They found that the C-terminal domain of SLF acts as a major pollen S specificity domain in vivo. Furthermore, alteration of a single C-terminal amino acid of SLF reversed its surface electrostatic potentials and subsequently the pollen S specificity. They also found the domain-swapped and point amino acid mutated SLFs are able to ubiquitinate non-self S-RNases, not self S-RNase, in consistent with their biochemical roles in SI.
Taken together, their results reveal that the electrostatic potentials act as a major physical force between cytosolic SLFs and S-RNases, providing a mechanistic insight into the self/non-self discrimination between cytosolic proteins in angiosperms.
This study entitled “Electrostatic potentials of the S-locus F-box proteins contribute to the pollen S specificity in self-incompatibility in Petunia hybrida” has been published online in The Plant Journal (DOI: 10.1111 /tpj. 13318).This work was supported by the National Basic Research Program of China and the National Natural Science Foundation of China.
Figure. An electrostatic potential model of “like charges repel and unlike charges attract” between SLFs and S-RNases. (Image by IGDB)
Dr. XUE Yongbiao