RESULTS
Transformation and Analysis ofTransgenic Rice Plants. The
plasmid pLAN150 (Fig. 1A) was cotransformed with the
hygromycin-resistance plasmid into protoplasts derived from
two varieties ofjaponica rice [Kinuhikari (K) and Nipponbare
(N)]. Of 238 hygromycin-resistant calli obtained from several
experiments, integration of the CP gene was detected in 139
calli by PCR analysis, giving a cotransformation frequency of
=60% at the DNA level. A total of 187 plants were regenerated
from 33 PCR-positive calli (lines).
Southern blot analysis of the primary transformants indicated
that one copy of the CP gene was integrated into the
genome of most transformants analyzed (Fig. 1B). No other
fragments of the CP gene were visualized under the conditions
used. This observation differs from those reported for
transgenic plants generated by direct DNA transfer showing
the presence of larger fragments in addition to a fragment of
the expected length (30, 31). When the circular plasmid was
used for transformation, a variety of integration patterns of
the plasmid were obtained (H. Fujimoto, T.I., R. Terada, R.
Yu, M. Suzuki, and K.S., unpublished data). Therefore, the
simple integration pattern of the RSV CP gene found in this
study may be due to linearization of the expression vector
before electroporation.