Abstract
Monoecious species provide an excellent system to study the specific determinants that underlie male and female flower development. Quercus suber is a monoecious species with unisexual flowers at inception. Despite the overall importance of this and other tree species with a similar reproductive habit, little is known regarding the mechanisms involved in the development of their male and female flowers. Here, we have characterised members of the ABCDE MADS-box gene family of Q. suber. The temporal expression of these genes was found to be sex-biased. The B-class genes, in particular, are predominantly, or exclusively (in the case of QsPISTILLATA), expressed in the male flowers. Functional analysis in Arabidopsis suggests that the B-class genes have their function conserved. The identification of sex-biased gene expression plus the identification of unusual protein-protein interactions suggest that the floral organ identity of Q. suber may be under control of specific changes in the dynamics of the ABCDE model. This study constitutes a major step towards the characterisation of the mechanisms involved in reproductive organ identity in a monoecious tree with a potential contribution towards the knowledge of conserved developmental mechanisms in other species with a similar sex habit.
Highlights
Development of separate male and female flowers in the same individual or in different individuals is a highly adaptive trait that enhances cross-pollination and gene fluidity[1]
Female inflorescences arise in spikes on the axils of new leaves containing three to eight individual flowers, that do not show any morphological evidence of aborted male organs[2], suggesting that both Q. suber male and female flowers are unisexual at inception
The main objective of this study was to study the potential involvement of MADS-box genes in floral organ identify of the Q. suber flowers, as unisexual flower development may be correlated to readjustments in gene expression programs in the different floral primordia
Summary
Development of separate male and female flowers in the same individual (monoecy) or in different individuals (dioecy) is a highly adaptive trait that enhances cross-pollination and gene fluidity[1]. The sliding boundaries model[20, 21] and the fading borders model[22] are modified ABCDE models for the development of flowers of lower eudicots, monocots and basal angiosperms Both models suggest that the unconventional flower phenotypes of these species are mainly due to alterations in the boundaries of the expression domains of B- and C-class genes. Not enough experimental evidence to explain how potential sex-determinant genes control the regulation of B or C- class expression in the early stages of floral organ determination of unisexual flowers by inception. Female inflorescences arise in spikes on the axils of new leaves containing three to eight individual flowers, that do not show any morphological evidence of aborted male organs[2], suggesting that both Q. suber male and female flowers are unisexual at inception
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