Flower development of Lilium longiflorum - The Lilium information ...

Chapter 7
functions from monocot genes using closely related species as a heterologous system
instead of making use of more diverged, dicot species.
These recent reports are providing good prospects for the possibilities of using
VIGS for reliable and straightforward reverse genetics in monocot species, including
the potential for easily and speedily studying gene function of flower homeotic genes
from grasses and bulbous species.
In the following sections, we present an overview of the genetic regulation of
flower development and propose using the VIGS system in functional characterization
of flowering genes.
MADS-box transcription factors and flower development
MADS-box genes code for transcription factors involved in developmental
pathways of eukaryotic organisms. In plants, they are implicated in diverse
developmental programs, such as root development, fruit ripening, dehiscence zones,
and especially, floral initiation and organ formation (Causier et al., 2002). The
Arabidopsis genome encompasses 107 MADS-box genes (Parenicová et al., 2003),
representing a significant portion of the developmental genes identified so far.
Floral initiation comprehends the process in which vegetative apical meristems
develop into floral meristems. The complete picture is still to be drawn but an already
complex network of genes involved in flower development pathways triggered by
light, temperature, nutrients and hormones was delineated (Blázquez, 2000), showing
several MADS box transcription factors playing fundamental functions in this process.
After floral initiation, transcription of homeotic genes is induced to form
sepals, petals, stamens and carpels in the floral meristem. Studies with Arabidopsis,
Antirrhinum and petunia led to the current ABCDE model for flower development in
which many MADS-box homeotic transcription factors execute essential roles.
The ABCDE model explains the flower formation as the result of differential
expression of homeotic genes, in which sepals, petals, stamens and carpels are formed
by the respective expression of genes with A, A+B+E, B+C+E and C+E functions.
Next to this partially overlapping expression pattern, class A and C genes are
functionally antagonists, and C + E functions are also involved in floral determinacy
(Coen and Meyerowitz, 1991; Ferrario et al., 2003; Goto et al., 2001; Pelaz et al.,
2001). Additionally, the D functional genes act in ovule formation (Angenent et al.,
1995).
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