Unraveling plant sex chromosome turnover through recent genomic studies

Sex chromosome-based sex determination (SD) systems have evolved from autosomes in many animals and some plants. Suppression of recombination around the SD locus drives the differentiation of X/Y or Z/W pairs, often resulting in the degeneration of the Y (or W) chromosome. Despite this vulnerability, sexual reproduction remains stable through compensatory mechanisms, one of which is ‘turnover’, the replacement of one sex chromosome system by another. While ‘turnover’ is relatively rare in mammals, it occurs more frequently in fish and amphibians. Recent genomic studies have shown that ‘turnover’ also occurs in plants. In poplar and willow, the duplication and relocation of the SD gene to another autosome suggests ‘turnover’ events. In Silene latifolia, the Y chromosome retains a masculinisation gene (GSFY), whereas the X chromosome harbours a feminisation gene (SlWUS1). As the Y chromosome degenerates, GSFY may be lost. In this scenario, turnover may occur if SlWUS1 expression increases as a feminising SD gene, shifting from an XY-type SD system to an X/A-type system. Although further analysis is needed in Silene, these findings suggest that plants may have turnover mechanisms, as in animals, to compensate for the loss of sex chromosomes. Insights into plant turnover emphasise that it is not limited to animals and is a general evolutionary process common to plants and animals.