The Chimeric REpressor gene-Silencing Technology (CRES-T) system is a novel reverse genetic method using a chimeric transcriptional repressor fusing an EAR transcriptional repression domain called SRDX. We sought to change the flower shape of
Pharbitis nil, a model ornamental flower, using an
Arabidopsis transcription factor fused with SRDX. For the first trial modulating flower shape we transformed with the class-C MADS-box transcription factor AGAMOUS (AG) fused with SRDX (
AGSRDX). Defects in class-C genes cause double flowers in
Arabidopsis and
Pharbitis. However, when
AGSRDX was expressed under the CaMV 35S promoter (
p35S), the transgenic
Pharbitis bore a malformed flower with a protruding pistil. We then used
DUPLICATED (
DP), one of the class-C genes in
Pharbitis. The
p35S::DPSRDX-introduced callus were difficult to regenerate during transgenic steps, but occasionally made a perfect double flower bud showing severe growth defects. The flower buds never developed to flower opening stage. These results indicate that CRES-T is functional in
Pharbitis but even using a conserved transcription factor, some species-specific variation might exist. To avoid these unwanted effects, we recruited inducible promoters to control expression of the chimeric transcription repressors in combination with the DNA-binding domain of GAL4 in yeast fused with SRDX and the GAL4 upstream activator sequence (UAS). Normal regeneration was observed by inducible repression of
DPSRDX during
in vitro redifferentiation, and the double-flowered
Pharbitis was generated. We successfully induced a non-transformant (NT)-like flower in
DPSRDX-expressing double-flowered transformants. Our approach will enable us to breed transgenic horticultural plants with inducible fertility.
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