Self-incompatibility in Brassicaceae crops: lessons for interspecific incompatibility

Abstract

Most wild plants and some crops of the Brassicaceae express self-incompatibility, which is a mechanism that allows stigmas to recognize and discriminate against “self” pollen, thus preventing self-fertilization and inbreeding. Self-incompatibility in this family is controlled by a single S locus containing two multiallelic genes that encode the stigma-expressed S-locus receptor kinase and its pollen coat-localized ligand, the S-locus cysteine-rich protein. Physical interaction between receptor and ligand encoded in the same S locus activates the receptor and triggers a signaling cascade that results in inhibition of “self” pollen. Sequence information for many S-locus haplotypes in Brassica species has spurred studies of dominance relationships between S haplotypes and of S-locus structure, as well as the development of methods for S genotyping. Furthermore, molecular genetic studies have begun to identify genes that encode putative components of the self-incompatibility signaling pathway. In parallel, standard genetic analysis and QTL analysis of the poorly understood interspecific incompatibility phenomenon have been initiated to identify genes responsible for the inhibition of pollen from other species by the stigma. Herewith, we review recent studies of self-incompatibility and interspecific incompatibility, and we propose a model in which a universal pollen-inhibition pathway is shared by these two incompatibility systems.

Structural basis for specific self-incompatibility response in Brassica

“…While the eSRK9-interacting residues from both the α-helix and β-sheet of SCR9 are relatively scattered along the length of this protein (Supplementary information, Figure S3A), nearly all of the SCR9-interacting residues in eSRK9 are located in the three hv regions ( Figure 4E and Supplementary information, Figure S4), supporting an important role of these regions in SCR recognition as previously suggested [2,12,[18][19][20][21]. Although all three hv regions are involved in SCR9 recognition, the hvI and hvII regions contribute the majority of SRK9 interaction with SCR9.…”

“…In the Brassicaceae family, SI is mediated by variant haplotypes of a single highly polymorphic genetic locus, termed the S locus [2], which generally contains three highly polymorphic genes, the stigma-expressed S-locus receptor kinase (SRK), the pollen-expressed S-locus cysteine-rich protein (SCR; or S-locus protein 11) and the S-locus glycoprotein (SLG) [3][4][5][6][7]. Genetic and biochemical studies established SRK and SCR as the sole determinants of SI specificity, and SRK as the receptor for SCR, which allows the stigma to discriminate between "self" and "non-self" pollen in the SI response [4,[8][9][10][11].…”

Pollen-Pistil Interactions and Their Role in Mate Selection

“…In UI, for example, it is possible that S-RNases are not involved in pollen recognition per se but rather function downstream in signaling or inhibitory components of the pollen-rejection pathway. This type of system -separate recognition systems coupled to a common downstream pathwayhas been proposed in Poaceae (Heslop-Harrison, 1982) and Brassicaceae (Kitashiba and Nasrallah, 2014). In fact, the rapid interspecific pollen tube rejection seen in UI (Fig.…”

Evaluation of crossability studies between selected eggplant accessions with wild relatives S. torvum, S. anguivi and S. aethopicum (Shum group)

“…This phenomenon of hybridization success in only one direction has been ascribed varyingly to unilateral incompatibility (UI), interspecific incompatibility (IC), unilateral hybridization (UH), unilateral inhibition (UI), unidirectional crossability, and one-way isolation among others with the basic principle of inhibition of pollen growth by cells of the pistilate parent or the incompatible relationship between embryo and endosperm leading to embryo abortion during the early stages of development (Abdalla and Hermsen, 1972;Kitashiba and Nasrallah, 2014). Although UI is generally exhibited in selfcompatible (SC) × self-incompatible (SI) species which has resulted in the generalization of SI being controlled by genes of the S-locus that are responsible for recognition of self-pollen by the stigma (Franklin-Tong and Franklin, 2000); there are various examples where one way cross has been observed not only in SC × SI species, but also between two SC or two SI species (Abdalla, 1970;Abdalla and Hermsen, 1972;Camadro and Peloquin, 1981).…”