Self-Incompatibility Mechanisms in Angiosperm Plants

Self-incompatibility (SI) in flowering plants is a genetically controlled prezygotic barrier that prevents self-fertilisation and promotes outcrossing. Two principal SI systems dominate angiosperms: sporophytic self-incompatibility, exemplified by Brassica species, and gametophytic self-incompatibility, which is widespread in Solanaceae, Rosaceae, Plantaginaceae and Rutaceae. In the gametophytic system, the pistil-specific S-RNase acts as the female determinant, while multiple S-locus F-box (SLF) proteins in pollen recognise non-self S-RNases and target them for degradation via an SCF (Skip–Cullin–F-box) E3 ubiquitin ligase complex. Self-recognition leads to retention of S-RNase activity, degradation of actin cytoskeletal elements and inhibition of pollen tube growth. In the sporophytic system, cell-surface receptor kinases and their pollen coat ligands mediate recognition and downstream signalling that blocks incompatible pollen. The S-locus itself is exceptionally polymorphic and often flanked by transposable elements, reflecting strong balancing selection. Modifiers unlinked to the S-locus can further influence the breakdown or maintenance of SI, leading to transitions between self-incompatibility and self-compatibility (SC). Understanding SI mechanisms is essential for plant breeding, hybrid seed production and the maintenance of genetic diversity in wild and cultivated taxa.

Research from Nature Portfolio

Recent studies have revealed novel genetic interactions that disrupt SI without direct mutation of S-locus determinants. In Arabidopsis lyrata, self-compatibility arises when specific S-alleles combine with an unlinked, allele-specific modifier that functionally impairs the corresponding S-RNase, demonstrating that SI breakdown can occur via epistatic interactions outside the S-locus. In diploid potato breeding, a non-S-locus F-box gene (Sli) was identified that interacts broadly with diverse pistil S-RNases, acting as a general inhibitor. Introduction of Sli into self-incompatible lines confers stable self-compatibility, opening a route to inbred hybrid potato production by circumventing the native gametophytic barrier.

Self-Incompatibility Mechanisms in Angiosperm Plants publication trend

The graph below shows the total number of articles in self-incompatibility mechanisms in angiosperm plants across all publications each year (not limited to Nature Index journals).

Technical terms

S-locus: The genomic region containing genes that determine pistil and pollen specificity in self-incompatibility systems.

S-RNase: A ribonuclease expressed in the pistil that recognises and degrades RNA in incompatible (self) pollen tubes, acting as the female SI determinant in gametophytic systems.

S-locus F-box (SLF) protein: A pollen-expressed F-box protein that recognises non-self S-RNases and recruits them to an SCF complex for ubiquitin-mediated degradation.

SCF complex: A multi-subunit E3 ubiquitin ligase (Skip–Cullin–F-box–Rbx1) that tags proteins for destruction by the proteasome.

Phase separation: The process by which biomolecules demix to form concentrated condensates, facilitating specific signalling or inhibitory reactions in the cell.

References

1. Breakdown of self-incompatibility due to genetic interaction between a specific S-allele and an unlinked modifier. Nature Communications (2023).
2. Phase separation of S‐RNase promotes self‐incompatibility in Petunia hybrida. Journal of Integrative Plant Biology (2024).
3. Transposable elements cause the loss of self‐incompatibility in citrus. Plant Biotechnology Journal (2023).
4. Long-read genome sequencing reveals the sequence characteristics of pear self-incompatibility locus. Molecular Horticulture (2025).
5. A nonS-locus F-box gene breaks self-incompatibility in diploid potatoes. Nature Communications (2021).