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[SANET-MG] MADS house for all



http://www.i-sis.org.uk/VFMH.phpISIS Press Release 09/03/05
View from MADS House
New opportunities for manipulating flowering in plants set the stage for
extensive alteration of crop geography Prof. Joe Cummins

A fully referenced version of this article is posted on ISIS members’
website. Details here

MADS-box genes are a large family of genes coding for protein
transcription-factors that recognize short stretches of DNA - the
MADS-box – to which they bind directly to regulate transcription.
MADS-boxes and transcription factors are present in all multi-cellular
eukaryotes from fungi to plants and humans where they regulate
developmental pathways. The MADS-box transcription factors bend DNA at
the site of transcription initiation to juxtapose transcription factors
on adjacent sites (boxes).

In plants, the MADS-box gene families are conserved among gymnosperms,
angiosperms, ferns and mosses. They serve a wide range of functions from
floral development to root formation, but the range of effects is not
yet fully explored. The controls of floral development pathways and time
of flowering have a common evolutionary origin. Flowering plants prefer
transcription from chromosomes of maternal rather than paternal origin
and even that epigenetic effect is mediated through MADS-box controls.

The discovery of the MADS-box gene families has had an instant impact on
agriculture and forestry. A wide array of inventions to control
flowering, seed production as well as other growth modifications has not
yet reached commercial farms and forests, but many modifications have
been reported and others have been patented. The main commercial
transgenic crops now available are modified for herbicide resistance or
insect resistance, the MADS-box constructions are modified with
flowering controls or flowering timing, even alterations in yield are
contemplated. Agronomy, horticulture and forestry will all be greatly
affected by the genetic modifications involving the MADS-box.

Much of the initial work on the plant MADS-box transcription factors was
done using the tiny mustard plant Arabidopsis. Recently a floral
transcription factor was found to control the agronomic traits of seed
yield and seed mass. Of course, such trait in Arabidopsis would mainly
please a few voles, but the trait can easily be manipulated in grain
crops such as maize, rice and wheat. In rice, for example, MADS-box
genes have been identified which control the timing of flowering. As
flowering time determines regional adaptability of rice varieties,
manipulating that timing will allow greater use of regional varieties.
Genes determining rice floral morphology have been identified allowing
rice spikelet development to be manipulated.

Vernalization is the long winter cold treatment required for flowering
in grain and some oil crops. Usually, the crops requiring vernalization
have spring planted cultivars that do not require the cold treatment so
they can be planted in spring rather than autumn. Nevertheless, the
winter requiring varieties have desirable traits that are not present in
the spring varieties. In wheat, vernalization is controlled by the
MADS-box gene WAP1. Unlocking vernalization should allow quality wheat
to be produced in warm climates. Bolting is another aspect of cold
temperature-induced flowering. Exposing the germinating seeds or
plantlets to a range of low temperatures accelerates flowering causing
cabbage or lettuce to lose commercial value. An anti-bolting MADS-box
gene has been identified in Chinese cabbage. The stage is set for
extensive alterations in crop geography.

The MADS-box genes expressed during tomato seed and fruit development
have been identified. Such findings may lead to commercial applications.

An anther-specific MADS-box was identified in peas and is expressed also
in a number of other plant species. The anther-specific transcription
regulator can be manipulated to produce male-sterile varieties used to
produce high value hybrid seeds.

A root nodule-specific MADS-box gene was identified in alfalfa root
nodules. Transferring nitrogen-fixing ability to non-legumes has been
discussed for decades, and this discovery may spur developments in that
area.

The MADS-box gene DAL1 was identified as a mediator of juvenile to adult
transition in Norway spruce. Hastening floral development in forest
trees can accelerate breeding programs.

The first of many patents on MADS-box related functions have begun to
appear, all of them broad patents covering reproductive development in
plants in general. United States Patent 6 828 478 provides the
surprising finding that ectopic expression of certain
MADS-box-containing gene products, such as SEP1, SEP2, SEP3 or AGL24,
combined with the ectopic expression of AP1, CAL or LFY gene products,
result in modulated reproductive development. Thus, this invention
provides plants comprising such ectopically expressible gene products as
well as methods of modulating the timing of reproductive development in
plants.

US patent 6 693 228 deals with the flowering locus (FLC) to delay or
advance flowering, and US patent 6 713 663, with FT protein that
modulates flowering in plants and dominant negative mutations of that
protein (dominant negative mutations usually disrupt the function of a
wild type gene by producing peptides that inactivate the wild type
product). A Canadian patent application deals with floral homeotic genes
for manipulation of flowering in poplar, and involves ablation of
reproductive cells using toxins activated by promoters for the flower
specific transcription factors, or by inhibiting the transcription
factors with genetic anti-sense or dominant negative mutants. In the
patents described above, the genes involved all originate from plants,
but selectable markers and synthetic genes are also used to modulate the
plant genes.

The discovery of MADS-box transcription regulators has open doors to
modulating a wide array of agronomical properties of which the control
of flowering and seed production is only the first. Other properties
include nitrogen fixation, plant growth and disease resistance. The
potential benefits from such manipulation must be evaluated alongside
the safety considerations, including the genetic modifications
themselves, which may involve synthetic genes and ablation toxins that
pose a threat to animals. Indeed, the homology between plant and animal
MADS-box genes should receive special attention.



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