Annual Report 2006

metabolites in plant tissue.
Cytochrome P450 monooxygenase plays an
important role in the oxidative metabolism of
xenobiotics in higher plants as well as in
mammals. The enzyme system on microsomes
consists of many P450 species and a few
NADPH-cytochrome P450 oxidoreductase
molecules. Agrochemicals including herbicides
were metabolized by P450 species, conjugated
with glutathione or sugars, and
compartmentalized into vacuoles, or cell walls,
in plant body. The oxidation by P450 species is
considered to be the limiting step of metabolism
of foreign chemicals.
Rice genome contained 246 P450 genes, but
the P450 species involved in xenobiotic
metabolism have not been studied well yet.
However, mammalian P450 species involved in
the xenobiotic metabolism have a high activity
to metabolize various herbicides with different
modes of action and in different chemical
functional groups.
We produced three types of transgenic rice
plants expressing human P450 species, CYP1A
1 or CYP2B6 or three P450s, CYP1A1, CYP2B6
and CYP2C19 simultaneously. The transgenic
rice plants had an enhanced ability to
metabolize herbicides with different chemical
structures owing to the introduced P450s. The
chemicals were supposed to be absorbed by the
transgenic plants in the fields and metabolized
rapidly into non-phytotoxic compounds.
Therefore, they exhibited a remarkable crosstolerance
toward various herbicides.
The transgenic rice plants expressing P450
s involved in xenobiotic metabolism are quite
useful for reducing the residual herbicides in
plants. I addition, they can be used for
phytoremediation of various chemicals that are
widespread in agricultural environments.
Development of male sterile
transgenic crops for the gene
confinement in transgenic crops
The possibility of gene transfer from
transgenic corps to wild relatives or nontransgenic
crops has often been cited as an
environmental and consumers concern.
Commercialized transgenic crops have already
been confirmed food and feed safety and
influence on biodiversity by authorities.
However, gene confinement technology must
be important to achieve co-existence and
utilization of future generations of transgenic
crops.
We have been developing to develop male
sterile transgenic crops using several molecular
approaches for gene confinements. We cloned
tapetum or anther specific expressed genes
from and and isolated
promoter region by 5-Race. Then tissue and
time specificity of isolated promoters were
confirmed by GUS expression. We could not
detect GUS expression except in anther using
several promoters such as BoA3, BoMS2, BrA6,
BrMS2 (Fig. 3 A). But other promoters induced
GUS expression not only tapetum and anther
but in petal, ovule and other tissues. We have
also isolated nine genes, which have the
potentiality of inducing male sterility, including
ribonuclease, protease, apoptosis related genes
and phytohormone biosynthesis related genes
from genus. And we constructed
vectors to combine the promoters and those
isolated gene. Subsequently we demonstrated
effects of combination of promoters and those
Fig. 3
GUS gene expression in tapetum and induction of male
sterility
Tapetum specific GUS expression by the control of
promoter BoA3 (A) and male sterile flower of transgenic
(B).