Unilateral incompatibility gene ui1.1 encodes an S-locus F-box protein expressed in pollen of Solanum species

Significance Self-incompatibility (SI) in plants prevents inbreeding by rejection of pollen from closely related individuals of the same species. Unilateral interspecific incompatibility (UI) blocks cross-hybridization between related species, typically when the pollen donor is self-compatible and the pistil parent is self-incompatible. In this study, we show that ui1.1 , a pollen UI factor in tomato, encodes an S-locus F-box protein that is homologous to an SI gene that in Petunia determines pollen specificity. We previously showed that another pollen factor, ui6.1 , encodes a Cullin1 protein that functions in both UI and SI. Cullin1 and F-box proteins are components of SCF-type (Skp1, Cullin1, F-box) ubiquitin ligase complexes. The results provide further evidence that pollen rejection in UI involves biochemical mechanisms related to SI.