Epigenetic control of sexual phenotype in a dioecious plant,Melandrium album

Abstract

Melandrium album (syn. Silene latifolia) is a model dioecious species in which the Y chromosome, present only in heterogametic males, plays both a male-determining and a strict female-suppressing role. We showed that treatment with 5-azacytidine (5-azaC) induces a sex change to androhermaphroditism (an-dromonoecy) in about 21% of male plants, while no apparent phenotypic effect was observed in females. All of these bisexual androhermaphrodites (with the standard male 24, AA + XY karyotype) were mosaics possessing both male and hermaphrodite flowers and, moreover, the hermaphrodite flowers displayed various degrees of gynoecium development and seed setting. Southern hybridization analysis with a repetitive DNA probe showed that the 5-azacytidine-treated plants were significantly hypomethylated in CG doubles, but only to a minor degree in CNG triplets. The bisexual trait was transmitted to two successive generations, but only when androhermaphrodite plants were used as pollen donors. The sex reversal was inherited with incomplete penetrance and varying expressivity. Based on the uniparental inheritance pattern of androhermaphroditism we conclude that it originated either by 5-azaC induced inhibition of Y-linked female-suppressing genes or by a heritable activation of autosomal female-determining/promoting genes which can be reversed, on passage through female meiosis, by a genomic imprinting mechanism. The data presented indicate that female sex suppression in M. album XY males is dependent on methylation of specific DNA sequences and can be heritably modified by hypomethylating drugs.

Silene as a model system in ecology and evolution

“…A simple treatment of plant meristems with a cytosine analog, 5-azacytidine, can dramatically reduce the nuclear genome 5-methylcytosine content. It is surprising that the only phenotypic change observed with this treatment in male S. latifolia was sex reversal, manifested as frequent bisexuality of flowers in karyotypically male (XY) individuals (Figure 4) (Janousek et al, 1996). The inflorescences of these plants are mosaics of staminate and perfect flowers, consistent with epigenetic control (Vyskot, 1999).…”

Tissue-Specific Response to Experimental Demethylation at Seed Germination in the Non-Model Herb Erodium cicutarium

“…In particular, experimental demethylation with DNMTi has contributed to reveal the broad range of plant traits and developmental processes that are regulated through DNA cytosine methylation, because such experiments have been able to, among others, alter sex expression [15], modify growth, leaf traits, flowering time or fruit ripening (e.g., [17,18,21,[41][42][43][44]), and induce dwarfism at maturity [14,17]. The phenotypic consequences of the cell reprogramming associated to genome-wide demethylation, however, are not necessarily the same across species, genetic backgrounds, and cell lines [13].…”

“…In plants, DNMT inhibitors (DNMTi hereafter), mainly 5-azacytidine, 5-aza-2 -deoxycytidine, and zebularine, have proven useful to obtain epimutants with characteristic phenotypes that, at least in some cases, remained stable across multiple generations (e.g., [14][15][16][17][18]). Zebularine is chemically more stable, forms a reversible complex with DNMTs, and exhibits a weaker inhibition activity and cytotoxicity than azacytosine analogs [13].…”

Epigenetic regulation of sex ratios may explain natural variation in self-fertilization rates

“…Differential DNA methylation of promoters can suppress the transcription of either male or female specific loci, thus determining an individual's sex [56]. The inactivation of one X chromosome in female mammals [46] is a well-known example of epigenetic control, and there are indications that there is a similar mechanism in some dioecious plants [57]; experimental modification of DNA methylation in plants has also been shown to induce sex reversal [58]. For some time DNA methylation was hypothesized to be involved in sex determination of fish [59], and more recently methylation of the gonadal aromatase promoter (cyp 19a) has been related to the regulation of temperature-mediated sex ratios in two fish with environmental and genetic sex determination, the European sea bass (Dicentrarchus labrax) [40] and the half-smooth tongue sole (Cynoglossus semilaevis) [36], suggesting that DNA methylation is indeed a crucial mechanism linking environmental temperature and sex determination in some fish species.…”