Papaver self-incompatibility is controlled by two multiallelic idiomorphs

Self-incompatibility (SI) prevents self-fertilization through highly polymorphic genetic recognition at the S locus with multiple alleles. In Papaver rhoeas , the S determinants were previously identified as PrpS and PrsS . However, we found that PrpS-PrsS was absent in many S haplotypes. In this work, we report the identification of an alternative pair of polymorphic S genes, S locus oligopeptide transporter ( SOPT ) and S locus glycine-rich protein ( SGRP ), segregating at the S locus when PrpS-PrsS is absent. SOPT and SGRP display hallmark S determinant features and confer SI when heterologously expressed in Arabidopsis thaliana . Therefore, instead of having allelomorphs with homologous variants, the Papaver SI system is determined by two multiallelic idiomorphs sharing no obvious common ancestry. This discovery of a dual-idiomorph system reveals a distinct genetic basis for polymorphism, with implications for the evolution of allorecognition mechanisms.