Plant contributions to our understanding of sex chromosome evolution

Abstract

52I.53II.53III.54IV.55V.55VI.56VII.57VIII.58IX.59X.59XI.61XII.6262References62 Summary A minority of angiosperms have male and female flowers separated in distinct individuals (dioecy), and most dioecious plants do not have cytologically different (heteromorphic) sex chromosomes. Plants nevertheless have several advantages for the study of sex chromosome evolution, as genetic sex determination has evolved repeatedly and is often absent in close relatives. I review sex‐determining regions in non‐model plant species, which may help us to understand when and how (and, potentially, test hypotheses about why) recombination suppression evolves within young sex chromosomes. I emphasize high‐throughput sequencing approaches that are increasingly being applied to plants to test for non‐recombining regions. These data are particularly illuminating when combined with sequence data that allow phylogenetic analyses, and estimates of when these regions evolved. Together with comparative genetic mapping, this has revealed that sex‐determining loci and sex‐linked regions evolved independently in many plant lineages, sometimes in closely related dioecious species, and often within the past few million years. In reviewing recent progress, I suggest areas for future work, such as the use of phylogenies to allow the informed choice of outgroup species suitable for inferring the directions of changes, including testing whether Y chromosome‐like regions are undergoing genetic degeneration, a predicted consequence of losing recombination.

Identification of RAN1 orthologue associated with sex determination through whole genome sequencing analysis in fig (Ficus carica L.)

“…In particular, RAN1 orthologue on the 100-kb region of scaffold seq000259 most closely matches the true A gene for the following reasons. (1) a number of sex linked markers located near RAN1 orthologue locus on Fc01a chromosome, (2) RAN1 orthologue locus positioned in the probably sex linked region23 (100-kb region), (3) RAN1 orthologue has the exclusive mutations that could account for the sex phenotypes of all genotypes including “Palmata” ( F. palmata ) possibly distantly related to other varieties (Fig. 4, Supplementary Table S13, Supplementary_Data_7), (4) RAN1 is involved in the transduction of ethylene which was reported to control sex phyenotype in some species2425.…”

Testing the translocation hypothesis and Haldane’s rule in Rumex hastatulus

“…The loss of recombination drives degeneration of some Bsporophytic^genes in the Y chromosome, but all vital genes necessary in male gametophyte have to be preserved (Chibalina and Filatov 2011;Charlesworth 2015;Crowson et al 2017). For this reason, the genetic information contained in the intact Y chromosome(s) is sufficient for the proper male gametophyte development but insufficient in the sporophyte.…”

“…Sex chromosomes in flowering plants are relatively young compared to mammalian ones; thus, they provide an excellent opportunity to study the early stages of differentiation of X/Y chromosomes and sex chromosome systems (Charlesworth 2002(Charlesworth , 2015Ming et al 2011). Generally, it is believed that the mechanisms of sex chromosome evolution are similar in plants and animals, but issues concerning plant sex chromosomes such as the rate and extent of addition and attrition of genetic material, localization, structure and function of sexdetermining regions, and the occurrence (or not) of dosage compensation mechanisms have not been well recognized yet (Vyskot and Hobza 2004;Charlesworth et al 2005;Charlesworth 2008;Ming et al 2011;Bergero et al 2015;Beaudry et al 2017;Crowson et al 2017;Muyle et al 2017).…”

Size and Content of the Sex-Determining Region of the Y Chromosome in Dioecious Mercurialis annua, a Plant with Homomorphic Sex Chromosomes

“…We might expect the magnitude of the cytological difference between homologous sex chromosomes to increase with their age, as the result of the progressive genetic degeneration of the Y or W chromosome (in species with XY or ZW systems, respectively). However, although there is some evidence for this expectation [9], there are many exceptions. For instance, in Coccinia grandis (Cucurbitaceae), a species that evolved dioecy about three million years ago [10], the X and Y chromosomes are highly divergent, with a 10% elongation of the Y compared to the X.…”