Next we looked at the effect that the presence of monocot
introns might have on GUS expression levels since the Ubi1 and
Act1 promoter-containing fragments used here also contain an
intron in their untranslated leader region (Fig. 1). It is well
established that addition of an intron such as the first introns from
the maize Adh1 and rice Act1 genes to the primary transcript can
dramatically increase gene expression levels in transformed monocots
(McElroy et al., 1991). For example, GUS expression in
transformed maize cells increased 6- and 60-fold when the Act1
and Adh1 first introns, respectively, were added to a 35S- gusA
chimeric gene. In contrast to maize, GUS expression was reduced
1.25- and 3-fold in Gladiolus when the Adh1 and Act1 first introns,
respectively, were added to a 35S- gusA chimeric gene (data not
shown). Results similar to those with Gladiolus were found when
petunia was bombarded with the exact same intron-containing
plasmids (data not shown). These results clearly indicated that
GUS expression was not stimulated in Gladiolus cells with the
addition of monocot introns to the gusA transcript. This observation
suggested that splicing of monocot introns may be relatively
inefficient in Gladiolus, a nongraminaceous monocot, as it is in
dicots such as petunia. Alternatively, stimulation in gene expression
by introns may be a feature that is generally limited to
graminaceous monocots like maize and rice.
Next we looked at the effect that the presence of monocotintrons might have on GUS expression levels since the Ubi1 andAct1 promoter-containing fragments used here also contain anintron in their untranslated leader region (Fig. 1). It is wellestablished that addition of an intron such as the first introns fromthe maize Adh1 and rice Act1 genes to the primary transcript candramatically increase gene expression levels in transformed monocots(McElroy et al., 1991). For example, GUS expression intransformed maize cells increased 6- and 60-fold when the Act1and Adh1 first introns, respectively, were added to a 35S- gusAchimeric gene. In contrast to maize, GUS expression was reduced1.25- and 3-fold in Gladiolus when the Adh1 and Act1 first introns,respectively, were added to a 35S- gusA chimeric gene (data notshown). Results similar to those with Gladiolus were found whenpetunia was bombarded with the exact same intron-containingplasmids (data not shown). These results clearly indicated thatGUS expression was not stimulated in Gladiolus cells with theaddition of monocot introns to the gusA transcript. This observationsuggested that splicing of monocot introns may be relativelyinefficient in Gladiolus, a nongraminaceous monocot, as it is indicots such as petunia. Alternatively, stimulation in gene expressionby introns may be a feature that is generally limited tograminaceous monocots like maize and rice.
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