Enhanced leaky sex expression is an adaptive plastic response to pollen limitation in the dioecious plant<i>Mercurialis annua</i>

Cossard, Guillaume; Pannell, John R.

doi:10.1101/703009

Cited by 2 publications

(2 citation statements)

References 94 publications

(94 reference statements)

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“…However, the ancient dioecy found in Salicaceae and the observation of small and heterogeneous levels of divergence in the basket willow [55] and poplar [43] sex chromosomes are difficult to reconcile with this twogene model, although it is of course still possible. Indeed, recent work has pointed out alternative sex determination mechanisms in flowering plants, either determined by a single gene as in the case of Diospyros [46] or, as in Cucumis and Mercurialis, as a polygenic trait controlled by several genes distributed across different chromosomes [100,101]. The Salicaceae family with its young sex chromosomes derived from ancient dioecy therefore provides a valuable comparative system to elucidate this process.…”

Section: Candidate Sex Determination Genes In S Viminalismentioning

confidence: 99%

Genome assembly of the basket willow, Salix viminalis, reveals earliest stages of sex chromosome expansion

et al. 2020

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Background: Sex chromosomes have evolved independently multiple times in eukaryotes and are therefore considered a prime example of convergent genome evolution. Sex chromosomes are known to emerge after recombination is halted between a homologous pair of chromosomes, and this leads to a range of non-adaptive modifications causing gradual degeneration and gene loss on the sex-limited chromosome. However, the proximal causes of recombination suppression and the pace at which degeneration subsequently occurs remain unclear. Results: Here, we use long-and short-read single-molecule sequencing approaches to assemble and annotate a draft genome of the basket willow, Salix viminalis, a species with a female heterogametic system at the earliest stages of sex chromosome emergence. Our single-molecule approach allowed us to phase the emerging Z and W haplotypes in a female, and we detected very low levels of Z/W single-nucleotide divergence in the non-recombining region. Linked-read sequencing of the same female and an additional male (ZZ) revealed the presence of two evolutionary strata supported by both divergence between the Z and W haplotypes and by haplotype phylogenetic trees. Gene order is still largely conserved between the Z and W homologs, although the W-linked region contains genes involved in cytokinin signaling regulation that are not syntenic with the Z homolog. Furthermore, we find no support across multiple lines of evidence for inversions, which have long been assumed to halt recombination between the sex chromosomes. Conclusions: Our data suggest that selection against recombination is a more gradual process at the earliest stages of sex chromosome formation than would be expected from an inversion and may result instead from the accumulation of transposable elements. Our results present a cohesive understanding of the earliest genomic consequences of recombination suppression as well as valuable insights into the initial stages of sex chromosome formation and regulation of sex differentiation.

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Section: Candidate Sex Determination Genes In S Viminalismentioning

confidence: 99%

Genome assembly of the basket willow, Salix viminalis, reveals earliest stages of sex chromosome expansion

et al. 2020

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“…2A, C). This difference indicates that leaky sex expression by M. annua females has a significant plastic component (21). Although plasticity is often interpreted as being adaptive, this has rarely been demonstrated convincingly in the literature (22,23).…”

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confidence: 98%

Rapid dissolution of dioecy by experimental evolution

Cossard¹,

Gerchen²,

Li³

et al. 2019

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Evolutionary transitions from hermaphroditism to dioecy have been frequent in flowering plants, but recent analysis indicates that reversions from dioecy to hermaphroditism have also been common. Here, we use experimental evolution to expose a mechanism for such reversions. We removed males from dioecious populations of the windpollinated plant Mercurialis annua and allowed natural selection to act on the remaining females that varied in their propensity for the occasional production of male flowers; such 'leaky' sex expression is common in both males and females of dioecious plants. Over only four generations, females evolved a 23-fold increase in average male-flower production. The phenotypic masculinization of females was also sufficient to render them effective at siring progeny in the presence of males. Our study illustrates the rapid dissolution of dioecy and the evolution of functional hermaphroditism under conditions that may frequently occur during periods of low population density, repeated colonization, or range expansion. It thereby experimentally validates a mechanism for a major transition in plant sexual systems..

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Enhanced leaky sex expression is an adaptive plastic response to pollen limitation in the dioecious plantMercurialis annua

Cited by 2 publications

References 94 publications

Genome assembly of the basket willow, Salix viminalis, reveals earliest stages of sex chromosome expansion

Genome assembly of the basket willow, Salix viminalis, reveals earliest stages of sex chromosome expansion

Rapid dissolution of dioecy by experimental evolution

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