Abstract
Transmission ratio distortion (TRD) refers to a widespread phenomenon in which one allele is transmitted by heterozygotes more frequently to the progeny than the opposite allele. TRD is considered as a mark suggesting the presence of a reproductive barrier. However, the genetic and molecular mechanisms underlying TRD in rice remain largely unknown. In the present study, a population of backcross inbred lines (BILs) derived from the cross of a japonica cultivar Nipponbare (NIP) and an indica variety 9311 was utilized to study the genetic base of TRD. A total of 18 genomic regions were identified for TRD in the BILs. Among them, 12 and 6 regions showed indica (9311) and japonica (NIP) alleles with preferential transmission, respectively. A series of F2 populations were used to confirm the TRD effects, including six genomic regions that were confirmed by chromosome segment substitution line (CSSL)-derived F2 populations from intersubspecific allelic combinations. However, none of the regions was confirmed by the CSSL-derived populations from intrasubspecific allelic combination. Furthermore, significant epistatic interaction was found between TRD1.3 and TRD8.1 suggesting that TRD could positively contribute to breaking intersubspecific reproductive barriers. Our results have laid the foundation for identifying the TRD genes and provide an effective strategy to breakdown TRD for breeding wide-compatible lines, which will be further utilized in the intersubspecific hybrid breeding programs.
Highlights
Reproductive isolation is recognized as a powerful driving force for maintaining species identity (Ouyang et al, 2010; Dagilis et al, 2018)
The high-density bin map was generated with 3,235 bins as markers, which were evenly distributed on all of the 12 chromosomes, and the bin lengths ranged from 30 kb to 3.0 Mb with an average of 115 kb in these 400 backcross inbred lines (BILs)
We have identified 18 Transmission ratio distortion (TRD) regions in which the alleles segregated abnormally in the BIL population that was derived from the intersubspecific cross of NIP and 9311
Summary
Reproductive isolation is recognized as a powerful driving force for maintaining species identity (Ouyang et al, 2010; Dagilis et al, 2018). An important genetic factor maintaining reproductive isolation is transmission ratio distortion (TRD), which is defined as the allele inheritance in progenies of hybrids that show a statistically significant deviation from the expected Mendelian segregation ratios, leading to deviations in genotype frequencies (Koide et al, 2012; Leppala et al, 2013; Li et al, 2019). TRD acts as one of the selfish genetic elements, distorting segregation or non-Mendelian transmission of alleles that can alter allele transmission in hybrids among progenies of heterozygotes, since the gametes carrying competing alleles increase their transmission over other alleles Three genes in fission yeast (Schizosaccharomyces kombucha and Schizosaccharomyces pombe), cw, cw27, and wtf, from the selfdriver wtf (for with Tf ) gene family encode both a gamete-killing poison and an antidote to the poison such that non-protected S. pombe (Sp) gametes are killed, and there is a loss of transmission of the Sp allele from heterozygotes (Hu et al, 2017; Nuckolls et al, 2017)
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