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

The potential of VIGS in functional genetics of transcription factors
In monocot species, despite many cases of significant differences in floral
structure, the ABCDE model appears to be applicable, but with reservations
(Nagasawa et al., 2003). Monocot genes showing homologous ABCDE functions have
already been identified (reviewed by Fornara et al., 2003). Rice and maize are model
species for flower development in grasses and the expression pattern of ABCDE genes
is helping to clarify the organ homology between flowers from grasses and other
species, considering that this topic has been a matter of discussion for a long time.
In bulbous species, such as hyacinth (Hyacinthus orientalis), lily (Lilium spp.),
narcissus (Narcissus pseudonarcissus), and orchids (Oncidium sp. and Dendrobium
sp.), MADS-box genes involved in flower development are also being isolated and
functionally characterized (Li et al., 2002; Tzeng and Yang, 2001; Tzeng et al., 2002;
Hsu and Yang, 2002; Yu and Goh, 2000). Liliaceae species show an interesting floral
aspect with the perianth organs (sepals and petals) evolving into petal-like structures,
receiving the designation of “tepals”. This feature led to the proposition of a modified
ABCDE model for the Liliaceae family members, with its B function being extended
to the first whorl, in order to cope with petal characteristics of this organs (van Tunen
et al., 1993).
Perspectives for reverse genetics of floral transcription factors based on VIGS
Overexpression of genes transcribing hpRNA of several genes involved in
flower developmental pathways leads to specific and heritable silencing of the
endogenous genes, resulting in null phenotypes in Arabidopsis (Chuang and
Meyerowitz, 2000).
VIGS of a regulatory flower developmental gene was first accomplished in N.
benthamiana with its LEAFY/FLORICAULA orthologue, NFL (Ratcliff et al., 2001),
opening avenues for using this system for efficient characterization of floral gene
functions.
Homeotic transcription factors, including the MADS-box genes involved in the
ABCDE model, are perfectly suitable for assessing their function via VIGS, since they
can instigate clear null phenotypes. They present a sequence structure conserved
throughout evolution, that may permit studies of reverse genetics in heterologous
systems, especially in model species in which VIGS is easily manipulated, such as N.
benthamiana and, perhaps, rice.
Our hypothesis is that a VIGS vector carrying a fragment of a homeotic
transcription factor would trigger transient silencing of its endogenous homologue and
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