Abstract
As a genetic mechanism to prevent self-fertilization, the plants in Solanaceae adopt the S-RNase-based self-incompatibility (SI) system, in which S-ribonuclease (S-RNase) and S-locus F-box (SLF) have been identified as female- and male-specificity determinants, respectively. It was postulated that S-RNase functions as a cytotoxin inhibiting pollen-tube growth, and that SLF specifically detoxifies non-self S-RNases via the ubiquitin-26S-proteasome system, thereby allowing compatible pollinations. However, it remained puzzling how SLF, with much lower allelic sequence diversity than S-RNase, might have the capacity to recognize a large repertoire of non-self S-RNases. We used in vivo functional assays and protein interaction assays to show that in Petunia (Solanaceae), at least three types of divergent SLF proteins (type-1, -2 and -3 SLFs) function as the pollen determinant, each recognizing a subset of non-self S-RNases. Our findings reveal a collaborative non-self recognition system in plants.
