Auxin-Dependent Patterning and Gamete Specification in the Arabidopsis Female Gametophyte

Abstract

The female reproductive unit of flowering plants, the haploid female gametophyte, is highly reduced relative to other land plants. We show that patterning of the Arabidopsis female gametophyte depends on an asymmetric distribution of the hormone auxin during its syncitial development. Furthermore, this auxin gradient is correlated with location-specific auxin biosynthesis, rather than auxin efflux that directs patterning in the diploid sporophytic tissues comprising the rest of the plant. Manipulation of auxin responses or synthesis induces switching of gametic and nongametic cell identities and specialized nonreproductive cells to exhibit attributes presumptively lost during angiosperm evolution. These findings may account for the unique egg cell specification characteristic of angiosperms and the formation of seeds with single diploid embryos while containing endosperm that can have variable numbers of parental haploid genomes.

ER-localized auxin transporter PIN8 regulates auxin homeostasis and male gametophyte development in Arabidopsis

“…On account of its differential distribution within plant tissues, it acts as a versatile coordinative signal mediating a multitude of processes, including female gametophyte patterning, embryogenesis, organogenesis, meristem activity, growth responses to environmental stimuli and others [7][8][9][10] . High auxin concentration in germinating pollen and active auxin responses in developing pollen [11][12][13] implicated auxin also in male gametophyte development and function, but its role there remained elusive.…”

Plant Somatic Embryogenesis: Some Useful Considerations

“…This polarity in the embryo sac is due to a gradient of the natural auxin indole-acetic acid along the micropyle-chalaza axis whose expression starts at the micropylar region outside of the embryo sac. In the same manner and following this pattern, the haploid egg cell which after its fertilization produces the embryo, is also highly polarized with its nucleus located at the chalazal pole (Pagnussat et al, 2009). Pagnussat et al (2009) reported that it is possible that auxin does not regulate the position of the nuclei during the embryo sac formation, however it participates in the regulation of cell fate at cellularization.…”

“…In the same manner and following this pattern, the haploid egg cell which after its fertilization produces the embryo, is also highly polarized with its nucleus located at the chalazal pole (Pagnussat et al, 2009). Pagnussat et al (2009) reported that it is possible that auxin does not regulate the position of the nuclei during the embryo sac formation, however it participates in the regulation of cell fate at cellularization. After fertilization, the resulting diploid zygote remains highly polarized, while the other male gamete fuses with the central cell of the embryo sac which then develops into the triploid endosperm, acting as a nutritive and protective element for the embryo.…”

An EAR-Dependent Regulatory Module Promotes Male Germ Cell Division and Sperm Fertility in Arabidopsis

“…The cellularization and differentiation of cells in the embryo sac appear to be transcriptionally regulated (Rabiger and Drews, 2013), and mechanisms involving RNA splicing and auxin and peptide signaling specify female gametic cells (Gross-Hardt et al, 2007;Pagnussat et al, 2009;Lieber et al, 2011;Lituiev et al, 2013). For male germline development, a regulatory framework for cell cycle progression and gamete specification has been established Borg and Twell, 2010;Twell, 2011).…”