Identification of transcription-factor genes expressed in the Arabidopsis female gametophyte.

Background: In flowering plants, the female gametophyte is typically a seven-celled structure with four cell types: the egg cell, the central cell, the synergid cells, and the antipodal cells. These cells perform essential functions required for double fertilization and early seed development. Differentiation of these distinct cell types likely involves coordinated changes in gene expression regulated by transcription factors.

Localization of the Arabidopsis histidine phosphotransfer proteins is independent of cytokinin.

Cytokinins are a class of mitogenic plant hormones that influence shoot and root growth, vascular and photomorphogenic development, leaf senescence, and many other aspects of plant growth and development. The Arabidopsis histidine phosphotransfer proteins (AHPs) play an important role in cytokinin signaling by bridging the perception of cytokinins by plasma-membrane receptors to the activation of cytokinin-responsive transcription factors. Based on previous microscopic observations, a model was developed in which the AHPs were thought to relocalize from the cytosol into the nucleus in response to exogenous cytokinin.

The subcellular distribution of the Arabidopsis histidine phosphotransfer proteins is independent of cytokinin signaling.

Cytokinins are a class of mitogenic plant hormones that play an important role in most aspects of plant development, including shoot and root growth, vascular and photomorphogenic development and leaf senescence. A model for cytokinin perception and signaling has emerged that is similar to bacterial two-component phosphorelays. In this model, binding of cytokinin to the extracellular domain of the Arabidopsis histidine kinase (AHKs) receptors induces autophosphorylation within the intracellular histidine-kinase domain.

The MYB98 subcircuit of the synergid gene regulatory network includes genes directly and indirectly regulated by MYB98.

The female gametophyte contains two synergid cells that play a role in many steps of the angiosperm reproductive process, including pollen tube guidance. At their micropylar poles, the synergid cells have a thickened and elaborated cell wall: the filiform apparatus that is thought to play a role in the secretion of the pollen tube attractant(s). MYB98 regulates an important subcircuit of the synergid gene regulatory network (GRN) that functions to activate the expression of genes required for pollen tube guidance and filiform apparatus formation.

MYB98 positively regulates a battery of synergid-expressed genes encoding filiform apparatus localized proteins.

The synergid cells within the female gametophyte are essential for reproduction in angiosperms. MYB98 encodes an R2R3-MYB protein required for pollen tube guidance and filiform apparatus formation by the synergid cells. To test the predicted function of MYB98 as a transcriptional regulator, we determined its subcellular localization and examined its DNA binding properties.

AGL80 is required for central cell and endosperm development in Arabidopsis.

During plant reproduction, the central cell of the female gametophyte becomes fertilized to produce the endosperm, a storage tissue that nourishes the developing embryo within the seed. The molecular mechanisms controlling the specification and differentiation of the central cell are poorly understood. We identified a female gametophyte mutant in Arabidopsis thaliana, fem111, that is affected in central cell development.

VARICOSE, a WD-domain protein, is required for leaf blade development.

To gain insight into the processes controlling leaf development, we characterized an Arabidopsis mutant, varicose (vcs), with leaf and shoot apical meristem defects. The vcs phenotype is temperature dependent; low temperature growth largely suppressed defects, whereas high growth temperatures resulted in severe leaf and meristem defects. VCS encodes a putative WD-domain containing protein, suggesting a function involving protein-protein interactions.