Gigantea: Uncovering New Functions in Flower Development

Abstract

GIGANTEA (GI) is a gene involved in multiple biological functions, which have been analysed and are partially conserved in a series of mono- and dicotyledonous plant species. The identified biological functions include control over the circadian rhythm, light signalling, cold tolerance, hormone signalling and photoperiodic flowering. The latter function is a central role of GI, as it involves a multitude of pathways, both dependent and independent of the gene CONSTANS(CO), as well as on the basis of interaction with miRNA. The complexity of the gene function of GI increases due to the existence of paralogs showing changes in genome structure as well as incidences of sub- and neofunctionalization. We present an updated report of the biological function of GI, integrating late insights into its role in floral initiation, flower development and volatile flower production.

Keywords: Gene ontology; biological function; cellular localisation; circadian clock; floral scent; flower development; flowering time; molecular function.

Figure 1

Schematic representation of the clock model indicating interactions by autoregulatory feedback loops via transcriptional and post-translational activation and repression. The clock components are depicted according to their peak-time expression from left to right. Black bars indicate repression. Green arrowheads lines indicate activation of transcription. Fucsia arrowheads lines indicate proteasomal degradation. The red curve represents the expression of GI during the day. TOC1 is protected during the day from ZTL-induced proteasome degradation thanks to the direct protein-protein interaction of GI with ZTL. During the evening, ELF3 promotes the proteasome degradation of GI through its interaction with COP1, thus promoting the ZTL-dependent TOC degradation. Boxes indicate sets of genes acting in coordination. The PRR box: PRR 5,7,9—these proteins are sequentially expressed during the day, and all repress LHY and CCA1; GI-ZTL box—protein-protein interaction leads to ZTL maturation; ELF3-ELF4-LUX complex box—protein complex peaking at dusk.

Figure 2

Models of GIGANTEA dependent flowering time regulation in (a) Arabidopsis, (b) soybean, (c) rice (d) and maize under long day condition. Regulation of flowering through GI differs between LD and SD plants. In contrast to LD plant Arabidopsis, OsGI inhibits flowering in rice, an SD plant, because the FT ortholog Hd3a is repressed by Hd1, the CO ortholog.

Figure 3

Phenotypic characteristics in Petunia × hybrida plants with loss of GI1 function. Apical (a), median (b) and basal (c) leaves of wild type Petunia (left) compared to iRNA: PhGI1 leaves (right). (d) Vegetative growth architecture of Petunia wild type (left) compared to the loss of PhGI1 function (right). Petunia inflorescence appearance (e) of wild type (left) and PhGI1 silenced line (right). Abortive flower (f,g) schematic representation of variations in internode length and number of axillary shoot meristems (indicated by the green colour) between wild type plants (left) and iRNA: PhGI1 plants (right).