Genomics-based discrimination of 2n gamete formation mechanisms in polyploids: a case study in nonaploid Diospyros kaki ‘Akiou’

Abstract

Unreduced gametes (2n gametes), possessing double the haploid genome, whatever ploidy that happens to be, are a common source of ploidy variation in plant populations. First and second division restitution (FDR and SDR) are the dominant mechanisms of 2n gamete production; all else being equal, FDR gametes have a higher degree of heterozygosity, thus they are advantageous in breeding. The discrimination of these mechanisms from the consequence of hybridization is challenging, especially in higher polyploids, and usually requires information on centromere location. In this study, we propose a genotyping-based strategy to uncover the mechanisms of 2n gamete formation in progeny that has a higher ploidy than its parents. Simulation of 2n gamete production revealed that FDR and SDR pathways can be discriminated based on allele transmission patterns alone without information on centromere location. We applied this strategy to study the formation mechanism of a nonaploid Diospyros kaki ‘Akiou’, which was bred via hybridization between D. kaki hexaploid cultivars. The result demonstrated that ‘Akiou’ was derived from the fertilization of a normal female gamete by a 2n male gamete, and that this 2n gamete was produced through FDR. Consequently, the distinct duplex transmission pattern in the FDR gamete enabled us to infer the genomic characteristics of polyploid persimmon. The method could be tested only for the plant being polypoid, which allows for the ability to discriminate causes of 2n gamete formation using allele dosage in progeny, and will be useful in future studies of polyploid genomics.

Exploiting Unreduced Gametes for Improving Ornamental Plants

“…In FDR, pairing and split-up of homologous chromosomes fail to occur or occur at a low frequency in meiosis I ( Tang and Luo, 2002 ); but the second division proceeds normally, resulting in two sister chromatids of homologous chromosomes to move to opposite poles ( Hermsen, 1984 ). There are two types of FDR: a strict sense and a broad sense ( Sun et al, 2021 ). In the strict sense, there was no pairing and recombination, and chromosomes directly advance to the second division, resulting in 2 n gametes that are genetically identical to the parent.…”

“…(2) An increasing number of ornamental plant species has been found to produce 2 n gametes ( Table 1 ). The frequency of 2 n gamete occurrence typically ranges from 0.1 to 2.0%, but it could be much higher up to 10% in interspecific hybrids ( Kreiner et al, 2017a , b ; Sun et al, 2021 ). Many ornamental plants are actually interspecific hybrids ( Kato and Mii, 2012 ).…”

The DcPS1 cooperates with OSDLa during pollen development and 2n gamete production in carnation meiosis

“…The use of unreduced gametes in plant breeding has led to the establishment of sexual polyploids and has played an important role in the improvement of crops such as carnation [ 8 ], Japanese persimmon [ 9 ], lemon [ 10 ], lily [ 11 , 12 ], poplar [ 13 ], potato [ 14 ], rose [ 15 , 16 ] and rubber trees [ 17 ]. Triploids with important horticultural traits, such as vigorous growth and large flowers, were identified in tulip 2x × 2x hybrid progenies [ 18 ].…”