Chromosome Pairing in Polyploid Grasses

Abstract

Polyploids are species in which three or more sets of chromosomes coexist. Polyploidy frequently occurs in plants and plays a major role in their evolution. Based on their origin, polyploid species can be divided into two groups: autopolyploids and allopolyploids. The autopolyploids arise by multiplication of the chromosome sets from a single species, whereas allopolyploids emerge from the hybridization between distinct species followed or preceded by whole genome duplication, leading to the combination of divergent genomes. Having a polyploid constitution offers some fitness advantages, which could become evolutionarily successful. Nevertheless, polyploid species must develop mechanism(s) that control proper segregation of genetic material during meiosis, and hence, genome stability. Otherwise, the coexistence of more than two copies of the same or similar chromosome sets may lead to multivalent formation during the first meiotic division and subsequent production of aneuploid gametes. In this review, we aim to discuss the pathways leading to the formation of polyploids, the occurrence of polyploidy in the grass family (Poaceae), and mechanisms controlling chromosome associations during meiosis, with special emphasis on wheat.

Mechanistic Insights of High Temperature-Interfered Meiosis in Autotetraploid Arabidopsis thaliana

“…4). This phenotype supports the opinion that autotetraploid plants, in contrast to allotetraploids, preferentially undergo synapsis between four homologous chromosomes (Braz et al, 2021; Lloyd and Bomblies, 2016; Svačina et al, 2020). The unbalanced chromosome segregation at anaphase I could result from the difficulties in multivalent resolving in the meiocytes with a mixed existence of tetravalents and bivalents, as well as the ten bivalents (Yant et al, 2013).…”

“…WGD is a conserved phenomenon that contributes to genomic diversity and speciation in higher plants (Comai, 2005; Dubcovsky and Dvorak, 2007; Ren et al, 2018; te Beest et al, 2012; Van de Peer et al, 2020). Additional copies of genome, however, increase the complexity for homologous chromosomes to pair and synapse (Lloyd and Bomblies, 2016; Svačina et al, 2020; Yant et al, 2013). In our study, the autotetraploid Col-0 plants generate a low but consistently-detectable rate (∼4.53%) of aberrant meiotic products under normal temperature conditions (Fig.…”

“…It is believed that the increased sets of homologous chromosomes contribute to genome flexibility and confer the plants with enhanced tolerance to both endogenous genetic mutations, or exogenous environmental stresses (Comai, 2005; Del Pozo and Ramirez-Parra, 2015; Rao et al, 2020; te Beest et al, 2012; Van de Peer et al, 2020; Wu et al, 2020). However, the multiple chromosome sets also challenge genome stability by impacting homolog pairing and balanced chromosome segregation with associated reduced fertility or viability of plants (Comai, 2005; Otto, 2007; Santos et al, 2003; Svačina et al, 2020; Yant et al, 2013). It is proposed that polyploids have evolutionarily developed a moderate strategy that assures genome stability to a large scale by early-stage homoeologous chromosome sorting, chromosome axis-mediated MR modification, and/or by sacrificing an acceptable reduction of CO formation (Bomblies et al, 2016; Grandont et al, 2014; Lloyd and Bomblies, 2016; Morgan et al, 2020; Seear et al, 2020).…”

Homology-mediated inter-chromosomal interactions in hexaploid wheat lead to specific subgenome territories following polyploidization and introgression

“…Stable subgenome inheritance is a fundamental characteristic of polyploid species [ 40 , 41 ]. Besides the well-known suppression of homoeologous pairing conferred by the Ph1 locus [ 42 – 44 ], there may be additional mechanisms promoting the increased affinities for wheat chromosomes in the same subgenome.…”

Intermediate Inheritance with Disomic Tendency in Tetraploid Intergeneric Citrus × Poncirus Hybrids Enhances the Efficiency of Citrus Rootstock Breeding

“…The molecular mechanisms that regulate homologous chromosome pairing have mainly been studied in polyploidy grass. Knowledge remains limited, although several hypothesis have been proposed [96]. The first hypothesis is the preexistence of the pairing regulators in diploid progenitors [97,98].…”