A sex-chromosome mutation in Silene latifolia

Silene latifolia is dioecious, yet rare hermaphrodites have been found, and such natural mutants can provide valuable insight into genetic mechanisms. Here, we describe a hermaphrodite-inducing mutation that is almost certainly localized to the gynoecium-suppression region of the Y chromosome in S. latifolia. The mutant Y chromosome was passed through the megaspore, and the presence of two X chromosomes was not necessary for seed development in the parent. This result supports a lack of degeneration of the Y chromosome in S. latifolia, consistent with the relatively recent formation of the sex chromosomes in this species. When crossed to wild-type plants, hermaphrodites performed poorly as females, producing low seed numbers. When hermaphrodites were pollen donors, the sex ratio of offspring they produced through crosses was biased towards females. This suggests that hermaphroditic S. latifolia would fail to thrive and potentially explains the rarity of hermaphrodites in natural populations of S. latifolia. These results indicate that the Y chromosome in Silene latifolia remains very similar to the X, perhaps mostly differing in the primary sex determination regions

A new physical mapping approach refines the sex-determining gene positions on the Silene latifolia Y-chromosome

Sex chromosomes are particularly interesting regions of the genome for both molecular genetics and evolutionary studies; yet, for most species, we lack basic information, such as the gene order along the chromosome. Because they lack recombination, Y-linked genes cannot be mapped genetically, leaving physical mapping as the only option for establishing the extent of synteny and homology with the X chromosome. Here, we developed a novel and general method for deletion mapping of non-recombining regions by solving "the travelling salesman problem", and evaluate its accuracy using simulated datasets. Unlike the existing radiation hybrid approach, this method allows us to combine deletion mutants from different experiments and sources. We applied our method to a set of newly generated deletion mutants in the dioecious plant Silene latifolia and refined the locations of the sex-determining loci on its Y chromosome map

Comparison of MADS box gene expression in developing male and female flowers of the dioecious plant white campion.

The MADS box motif is common to genes that regulate the pattern of flower development. To determine whether MADS box genes also play a role in differentiation of the sexes in dioecious plants, we isolated cDNAs (SLM1 to SLM5, for Silene latifolia MADS) with MADS box homology from transcripts of male flower buds of the model dioecious species white campion and compared their expression in developing female and male flowers. SLM1 had extensive sequence similarity to the snapdragon MADS box gene PLENA, SLM2 to GLOBOSA, SLM3 to DEFICIENS, and both SLM4 and SLM5 were similar to SQUAMOSA. Each of the white campion MADS box genes was expressed in the same floral whorls as their respective most homologous snapdragon genes. The sex of the plant affected the pattern of SLM2 and SLM3 expression in the petal and stamen whorls, resulting in a smaller fourth whorl in male flowers than in female flowers. This was correlated with repressed gynoecium development in male flowers. The expression of SLM4 and SLM5 in both sexes differed from that of SQUAMOSA in one important aspect. Unlike SQUAMOSA, they were expressed in inflorescence meristems. This may reflect differences in growth pattern between white campion and snapdragon

Conserved expression of a TASSELSEED2 homolog in the tapetum of the dioecious Silene latifolia and Arabidopsis thaliana

Plant Journal123515-526PLJU