The X chromosome is necessary for ovule production in Silene latifolia

Abstract

Sex chromosomes stop recombining and accumulate differences over time. In particular, genes on the chromosome restricted to the heterogametic sex degenerate and become non-functional. Here, we investigated whether or not the degeneration of a plant Y chromosome was sufficient to cause ovules containing a Y to fail to develop, thereby eliminating the possibility of YY individuals. We used two genotypic assays to determine the genotype—XX, XY, or YY—of offspring from a single fruit of an otherwise normal male XY plant of Silene latifolia . The fruit contained fewer ovules than normal pistillate flowers, produced an equal offspring sex ratio, and generated no YY offspring. The results indicate that ovaries must contain an X chromosome to develop properly. While haploid selection has slowed down Y-chromosome degeneration in S . latifolia , we find that it has progressed sufficiently to prevent the proper development of ovules, and hence prevent the presence of YY individuals.

YY males of the dioecious plant Mercurialis annua are fully viable but produce largely infertile pollen

“…While it is possible that YY individuals suffer from mildly deleterious effects that we were unable to detect, or from effects on traits that we did not measure, the viability and phenotypic similarity between individuals with and without an X chromosome (or with a single or double dose of the Y) are in striking contrast with studies that show substantially poorer performance of YY males compared with their XY counterparts. For instance, Y‐chromosome degeneration has led to YY lethality in many animal species (Graves, ), as well as in the plants Rumex hastatulus (Smith, ), Silene latifolia (Westergaard, ; Janoušek et al ., ; Soukupova et al ., ; Veltsos & Delph, ), and Carica papaya (Liu et al ., ; Ming & Moore, ; Yu et al ., 2008a). These species probably have older sex chromosomes than M. annua, with a longer history of Y‐chromosome degeneration.…”

“…Here, WW hermaphrodites are viable but have substantially lower fitness than their ZW counterparts, pointing to recessive deleterious effects of W‐linked alleles (Sassaman & Weeks, ). In plants, YY individuals are nonviable in both Silene latifolia (Janoušek et al ., ; Soukupova et al ., ; Veltsos & Delph, ), which has highly divergent heteromorphic sex chromosomes (Krasovec et al ., ), and in Carica papaya , which has homomorphic sex chromosomes at the cytological level but shows XY divergence at the sequence level (Liu et al ., ; Yu et al ., 2008b). Viable YY males have been reported in Asparagus officinalis (Harkess et al ., ), Spinacia oleracea (Yamamoto et al ., ; Wadlington & Ming, ), Cannabis sativa (Peil et al ., ), Phoenix dactylifera and Actinidia chinensis (reviewed in Ming et al ., ).…”

Labile sex expression in angiosperm species with sex chromosomes

“…Completely monoclinous individuals (trioecy) have received some attention as they arise through deletions of parts of the Y chromosome and allow one to investigate the genetic architecture of dioecy in this species [2,71,89,90]. Leakiness does not seem to be caused by a mutation, at least in one report where it was found not to be heritable [91]. An extensive study of the occurrence of sexual lability has been performed by Frick & Cavers [69], who found both leakiness and sex changes by monitoring plants in common garden experiments and the greenhouse for several flowering seasons.…”