Self-incompatibility (SI) serves as a common mechanism within flowering plants to prevent fertilization by self-pollen, thereby ensuring healthy seed production. This intraspecific reproductive barrier is observed in various plant families such as Solanaceae, Plantaginaceae, Rosaceae, and Rutaceae. In these families, SI is regulated by a single polymorphic S-locus, housing the genetic information for critical components involved in the SI system.
The key players in this intricate process are the S-locus F-box box proteins (SLFs) and the pistil factor S-RNase components. Both of these elements are encoded by the S-locus, forming an interconnected network responsible for enforcing self-incompatibility. When a pollen grain carrying a matching S-allele attempts to fertilize a stigma with the same S-allele, the SI system is triggered, resulting in the rejection of the self-pollen and impeding the formation of seeds through self-pollination.
The SLFs, encoded by the S-locus, play a vital role in the male side of the SI system. These proteins are known to interact with specific pollen proteins, ultimately leading to their degradation within the pollen tube. By targeting these key pollen factors for destruction, the SLFs effectively hinder self-pollen tubes from successfully reaching the ovules, thus preventing self-fertilization.
On the other hand, the pistil factor S-RNases come into play on the female side of the SI system. These proteins, also encoded by the S-locus, are present in the pistil tissue surrounding the ovules. When self-pollen is recognized, the S-RNases exhibit ribonuclease activity and selectively degrade the pollen RNA, inhibiting its growth and causing it to abort before reaching the ovules. Through this mechanism, the pistil factors act as a defense system against self-pollination, ensuring cross-pollination and genetic diversity within the species.
It is worth noting that the S-locus exhibits polymorphism, meaning that there are multiple versions or alleles of this gene. This genetic variation leads to different combinations of SLFs and S-RNases in different individuals, resulting in a diversified SI system within the plant population. The polymorphic nature of the S-locus enhances the efficiency of self-incompatibility by increasing the repertoire of recognition and rejection mechanisms for self-pollen.
In conclusion, self-incompatibility is a prevalent reproductive barrier found in flowering plants, including families such as Solanaceae, Plantaginaceae, Rosaceae, and Rutaceae. The SI system in these plants is regulated by a single polymorphic S-locus, which encodes the crucial components SLFs and S-RNases. By employing a network of interactions and degradation processes, these components effectively prevent self-pollen from fertilizing ovules, ensuring successful reproduction through cross-pollination and the maintenance of genetic diversity within plant populations.
