Tissue-specific expression of the β-glucuronidase reporter gene in transgenic strawberry (Fragaria × ananassa) plants
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The strawberry (Fragaria spp) is regarded as a false fruit because it originates from the receptacle, which is a non-ovarian tissue. For this reason, fruit-specific promoters isolated from plant species in which the fruit is derived from the ovary wall might not be suited to control gene expression in a fruit-specific way in strawberry. In order to achieve (false) fruit-specific expression in strawberry, we tested the petunia FBP7 (floral binding protein7) promoter, which proved to be active in the receptacles of petunia flowers, in transgenic strawberry fruits. In strawberry plants containing the FBP7 promoter fused to the β-glucuronidase (GUS) reporter gene (gus), GUS activity was found in floral and fruit tissues of all developmental stages tested but not in leaf, petiole and root tissue. Surprisingly, Northern blot analysis showed the presence of gus-derived mRNAs in root (strong) and petiole (weak) tissue of fbp7-gus plants in addition to the floral and fruit tissues. Therefore, it is concluded that the histological GUS phenotype does not necessarily correspond with expression at the mRNA level. mRNA quantification using the TaqMan polymerase chain reaction technology confirmed the Northern results and showed that in red strawberry tissue the cauliflower mosaic virus 35S promoter is at least sixfold stronger than the FBP7 promoter.
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