Finding a Compatible Partner: Self-Incompatibility in European Pear (Pyrus communis); Molecular Control, Genetic Determination, and Impact on Fertilization and Fruit Set

Abstract

Pyrus species display a gametophytic self-incompatibility (GSI) system that actively prevents fertilization by self-pollen. The GSI mechanism in Pyrus is genetically controlled by a single locus, i.e., the S-locus, which includes at least two polymorphic and strongly linked S-determinant genes: a pistil-expressed S-RNase gene and a number of pollen-expressed SFBB genes (S-locus F-Box Brothers). Both the molecular basis of the SI mechanism and its functional expression have been widely studied in many Rosaceae fruit tree species with a particular focus on the characterization of the elusive SFBB genes and S-RNase alleles of economically important cultivars. Here, we discuss recent advances in the understanding of GSI in Pyrus and provide new insights into the mechanisms of GSI breakdown leading to self-fertilization and fruit set. Molecular analysis of S-genes in several self-compatible Pyrus cultivars has revealed mutations in both pistil- or pollen-specific parts that cause breakdown of self-incompatibility. This has significantly contributed to our understanding of the molecular and genetic mechanisms that underpin self-incompatibility. Moreover, the existence and development of self-compatible mutants open new perspectives for pear production and breeding. In this framework, possible consequences of self-fertilization on fruit set, development, and quality in pear are also reviewed.

Genetic Diversity and Structure of the Portuguese Pear (Pyrus communis L.) Germplasm

“…Mean heterozygosity values (Ho = 0.83 and He = 0.79) were similar to those found for local varieties and reported by other groups [18,[27][28][29][30]. This high level of observed heterozygosity results from the fact that pear is an outcrossing plant and also has gametophytic self-incompatibility [31]. Ghosh et al [32] found an observed heterozygosity equivalent to 0.63 and Hokanson et al [33] reported 0.62 when nine SSR loci were used to study 142 Malus accessions.…”

Pre- and Postzygotic Barriers Associated with Intergeneric Hybridization between Aronia melanocarpa (Michx.) Elliott x Pyrus communis L. and ×Sorbaronia dippelii (Zabel) CK Schneid. x Pyrus communis

“…dippelii. Our study was consistent with others showing that P. communis is selfincompatible (Claessen et al, 2019). Previous studies have suggested that Aronia and closely related intergeneric hybrids are compatible (Connolly, 2014;Leonard, 2011).…”

Segregation Distortion for Male Parents in High Density Genetic Maps from Reciprocal Crosses between Two Self-Incompatible Cultivars Confirms a Gametophytic System for Self-Incompatibility in Citrus

“…In legumes, the Solanaceae and Brassicaceae families were important models to decipher the molecular mechanisms of SI [10][11][12]. In fruit tree species, SI has been described in most species including the family Rosaceae (apple, pear, plum, and apricot [13][14][15][16]) and other families such as Malvaceae (cocoa [17]), Oleaceae (olive tree [18]) and Rutaceae (citrus species; Zhang et al [19] for a review).…”