Abstract
BackgroundThe rise and fall of the Y chromosome was demonstrated in animals but plants often possess the large evolutionarily young Y chromosome that is thought has expanded recently. Break-even points dividing expansion and shrinkage phase of plant Y chromosome evolution are still to be determined. To assess the size dynamics of the Y chromosome, we studied intraspecific genome size variation and genome composition of male and female individuals in a dioecious plant Silene latifolia, a well-established model for sex-chromosomes evolution.ResultsOur genome size data are the first to demonstrate that regardless of intraspecific genome size variation, Y chromosome has retained its size in S. latifolia. Bioinformatics study of genome composition showed that constancy of Y chromosome size was caused by Y chromosome DNA loss and the female-specific proliferation of recently active dominant retrotransposons. We show that several families of retrotransposons have contributed to genome size variation but not to Y chromosome size change.ConclusionsOur results suggest that the large Y chromosome of S. latifolia has slowed down or stopped its expansion. Female-specific proliferation of retrotransposons, enlarging the genome with exception of the Y chromosome, was probably caused by silencing of highly active retrotransposons in males and represents an adaptive mechanism to suppress degenerative processes in the haploid stage. Sex specific silencing of transposons might be widespread in plants but hidden in traditional hermaphroditic model plants.
Highlights
The rise and fall of the Y chromosome was demonstrated in animals but plants often possess the large evolutionarily young Y chromosome that is thought has expanded recently
We address the following questions: How much the Y chromosome varies among S. latifolia populations? Does this variation correlate with genome size? Is the Y chromosome still expanding in S. latifolia? Which repetitive elements dominantly contribute to Y chromosome expansion in S. latifolia? Are these repetitive elements the main contributors to genome size expansion?
Genome size varies more than Y chromosome size in S. latifolia ecotypes In order to assess possible intraspecific genome and Y chromosome size variation in S. latifolia, male and female genome size in seven distinct ecotypes from central and southern Europe was measured using flow cytometry
Summary
The rise and fall of the Y chromosome was demonstrated in animals but plants often possess the large evolutionarily young Y chromosome that is thought has expanded recently. To assess the size dynamics of the Y chromosome, we studied intraspecific genome size variation and genome composition of male and female individuals in a dioecious plant Silene latifolia, a well-established model for sex-chromosomes evolution. Only 19 plant species possess well-established sex chromosomes. Most of these species bear large Y chromosomes, suggesting an early expanding stage of sex chromosome evolution [1]. Expansion of mainly nonrecombining parts of sex chromosomes is frequently accompanied by accumulation of repetitive sequences. This often results in significant genome size variation among. S. latifolia (white campion) possesses a well-established sex determination system with the dominant Y chromosome in males. Contrary to the evolutionary old sex chromosomes in humans, S. latifolia sex chromosomes
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