Abstract
Meiosis is a key cellular process of sexual reproduction that includes pairing of homologous sequences. In many species however, meiosis can also involve the segregation of supernumerary chromosomes, which can lack a homolog. How these unpaired chromosomes undergo meiosis is largely unknown. In this study we investigated chromosome segregation during meiosis in the haploid fungus Zymoseptoria tritici that possesses a large complement of supernumerary chromosomes. We used isogenic whole chromosome deletion strains to compare meiotic transmission of chromosomes when paired and unpaired. Unpaired chromosomes inherited from the male parent as well as paired supernumerary chromosomes in general showed Mendelian inheritance. In contrast, unpaired chromosomes inherited from the female parent showed non-Mendelian inheritance but were amplified and transmitted to all meiotic products. We concluded that the supernumerary chromosomes of Z. tritici show a meiotic drive and propose an additional feedback mechanism during meiosis, which initiates amplification of unpaired female-inherited chromosomes.
Highlights
In eukaryotes, meiosis is a highly conserved mechanism that generates gametes and includes recombination and pairing of homologous chromosomes
Based on controlled experiments and tetrad analyses, we surprisingly found that the supernumerary chromosomes of Z. tritici are subject to a meiotic drive restricted to unpaired chromosomes inherited from the female parent
The experiments included a total of 39 crosses of IPO323/IPO323 chromosome deletion strains with IPO94269 resulting in different complements of paired and unpaired supernumerary chromosomes in the diploid zygote (Table 1, Supplementary file 1)
Summary
Meiosis is a highly conserved mechanism that generates gametes and includes recombination and pairing of homologous chromosomes. Supernumerary chromosomes have been described in a large variety of plant, animal and fungal species, including for example in 14% of karyotyped orthopteran insect species (Jones, 1995), 8% of monocots, and 3% of eudicot species (Levin et al, 2005). These chromosomes commonly show non-Mendelian modes of inheritance, leading to segregation distortion during meiosis and a change in the frequency of the supernumerary chromosome in the progeny – a process that has been described as
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