Fine mapping a self-fertility locus in perennial ryegrass

Abstract

A self-fertility locus was fine mapped to a 1.6 cM region on linkage group 5 in a perennial ryegrass population. This locus was the main determinant of pollen self-compatibility. In grasses, self-incompatibility (SI) is characterized by a two-loci gametophytic (S and Z) mechanism acting together in the recognition and inhibition of self-pollen. Mutations affecting the expression of SI have been reported in a few grass species. In perennial ryegrass (Lolium perenne L.), a mutation independent from S and Z, and mapping on linkage group 5 (LG 5), was previously reported to produce self-fertile plants. Here, we describe fine mapping of the self-fertility (SF) gene in a perennial ryegrass population and determine whether there is any effect of other genomic regions on the pollen compatibility. The phenotypic segregation of SF showed a bimodal distribution with one mean at 49% pollen compatibility and the other at 91%. Marker-trait association analysis showed that only markers on LG 5 were significantly associated with the trait. A single gene model explained 82% of the observed variability and no effects of the other regions were detected. Using segregation and linkage analysis, the SF locus was located to a 1.6 cM region on LG 5. The flanking marker sequences were aligned to rice and Brachypodium distachyon reference genomes to estimate the physical distance. We provide markers tightly linked to SF that can be used for introgression of this trait into advanced breeding germplasm. Moreover, our results represent a further step towards the identification of the SF gene in LG 5.

Identification of candidate genes for self-compatibility in perennial ryegrass (Lolium perenneL.)

“…In the homozygous state for the allele contributed by the SC parent (AA), m1042 was associated with an increase of > 40% in self-compatible pollen in an in vitro selfpollination assay. The QTL found coincided with the QTL reported in Do Canto et al (2018) as confirmed by the close physical proximity of m1042 and the two flanking markers, reported by Do Canto et al (2018), on the Italian ryegrass reference assembly (data not shown).…”

“…These additional genotyping data were used to generate a local linkage map and to estimate the genetic distances between those markers (Figure 3). The locus delimited by G05_065 and G06_096 spanned 1.44 cM, comparable to the genetic distance (1.6 cM) found by Do Canto et al (2018).…”

“…Mutations in loci non-allelic to S and Z can also lead to SC, by interrupting the downstream cascade triggered by the initial self-recognition (Do Canto et al 2016). Such putative mutations have been found in rye ( Secale cereale L.) and perennial ryegrass (Voylokov et al 1993; Egorova et al 2000; Thorogood et al 2005; Arias-Aguirre et al 2013, Do Canto et al 2018; Slatter et al 2020). A detailed molecular understanding of how SC arises in SI grasses is lacking, but several studies have acknowledged that calcium (Ca 2+ ) signaling plays an essential role in the recognition and/or inhibition of self-pollen (Yang et al 2009; Chen et al 2019).…”

“…It was concluded that SC was caused by a putative mutation in a major gametophytic gene mapped to a 16 cM locus on LG 5. Do Canto et al (2018) fine mapped the position of the locus to a 1.6 cM region. Despite providing evidence of one major locus explaining the SC variation, these two studies did not exclude the presence of additional major effects on other LGs.…”

Self-(In)compatibility Systems: Target Traits for Crop-Production, Plant Breeding, and Biotechnology

“…However, SC provides advantages to breeders including uniformity and propagation of parental inbreds and reduction of genetic load. Several routes to SC have been documented in grasses, including S-and Z-loci mutations (mainly pollen part defects) as well as other loci such as the T- (Thorogood et al, 2005) and the SF-loci (Do Canto et al, 2018). In practice, SC can be introgressed into populations of allogamous grasses by backcrossing.…”