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.
Highlights
Self-incompatibility (SI) refers to all genetic mechanisms in flowering plants that prevent self-fertilization through the recognition and rejection of self-pollen by the style of a flower (DeNettancourt, 1977)
Several SLFs thereby even appeared to target the same S-RNase (Sun and Kao, 2013; Matsumoto and Tao, 2016a). These findings suggest that the actual number of SFBB genes in Pyrus might be around 17–20, the exact number is still unknown
These results indicate that tip-localized reactive oxygen species (ROS) disruption occurs very early in the SI response in Pyrus, and putatively acts as a central trigger for pollen tube growth inhibition and programmed cell death (PCD) (Wang et al, 2010)
Summary
Self-incompatibility (SI) refers to all genetic mechanisms in flowering plants that prevent self-fertilization through the recognition and rejection of self-pollen by the style of a flower (DeNettancourt, 1977). In Pyrus, only a small number of spontaneous self-compatible mutants have been identified (Sawamura et al, 2013; Wu et al, 2013), most of which belong to the species Pyrus pyrifolia (Japanese pear – syn: Pyrus serotina) These selfcompatible Pyrus genotypes are most often the result of a pistil-part mutation, that either leads to a non-functional S-RNase or that reduces its expression in the style (Li et al, 2009; Sawamura et al, 2013; Wu et al, 2013). Recent advances on the genetic determination and molecular control of SI, and discuss breakdown of selfincompatibility and its impact on fruit development and final fruit set in pear
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