The genetics of sex determination in stinging nettle (Urtica dioica)

Abstract

Abstract:Urtica dioica ("stinging nettle") includes both dioecious and monoecious forms.In most sexually dimorphic angiosperm species, the genetic mechanisms of sex determination are completely unknown. The few species that include both monoecious and dioecious forms provide an unusual opportunity to examine the genetic mechanisms that underlie the separation of sexual functions, through crossing experiments and analysis of progeny segregation. Our focus is on the genetic mechanisms distinguishing monoecious and dioecious forms of U. dioica. A complicated picture of sex determination in this species has resulted from crosses between dioecious and monoecious subspecies, as well as between dioecious and monoecious forms of the same subspecies. Most significant is evidence for a maternal influence on sex determination and for the possibility of gynodioecy as an intermediate stage in the evolutionary pathway to dioecy.

Complex sex determination in the stinging nettle Urtica dioica

“…Further additional genes influence gender, so that the phenotype is not always as would be expected from the genotype at the major locus. The results of Shannon and Holsinger (2007) on U. dioica spp. dioica in the US and Canada are consistent with some of our findings.…”

“…Low frequencies of monoecious plants occur in U. dioica populations in the Netherlands (Heemskerk et al 1998;de Jong et al 2005) and other parts of Europe (GreigSmith 1948;Kay and Stevens 1986). Monoecious plants sometimes occur in higher frequencies (up to 10%) in crosses between male and female plants (Shannon and Holsinger 2007). Some plants showed a stable phenotype of a single gender, even under extremely different conditions, and these were designated as male or female .…”

“…In contrast, monoecious plants were generally labile and became largely male under benign conditions. Recently, Shannon and Holsinger (2007) also used U. dioica by making crosses, among others between U. dioica spp. dioica and the monoecious spp.…”

“…Since the monoecious species is homozygous at the sex determination locus, these results indicate that a pollen grain of B. dioica carries either the male A or female a-allele, whereas the embryo sac has only the a-allele. More recent studies that employed crosses between dioecious and monoecious forms include Dorken and Barrett (2004) and Shannon and Holsinger (2007).…”

“…Under laboratory conditions U. dioica flowers within 2 months from germination, making it particularly suitable for experiments. The proportion male flowering plants in the field and/or SSR vary considerably in European (Kay and Stevens 1986;de Jong et al 2005;Glawe 2006) and North American populations (Shannon and Holsinger 2007). The mechanism of genetic sex determination has been poorly characterised in U. dioica.…”