Optimisation of transgene action at the post-transcriptional level: high quality parthenocarpic fruits in industrial tomatoes.
BACKGROUND
Genetic engineering of parthenocarpy confers to horticultural plants the ability to produce fruits under environmental conditions that curtail fruit productivity and quality. The DefH9-iaaM transgene, whose predicted action is to confer auxin synthesis specifically in the placenta, ovules and derived tissues, has been shown to confer parthenocarpy to several plant species (tobacco, eggplant, tomato) and varieties.


RESULTS
UC82 tomato plants, a typical cultivar used by the processing industry, transgenic for the DefH9-iaaM gene produce parthenocarpic fruits that are malformed. UC82 plants transgenic for the DefH9-RI-iaaM, a DefH9-iaaM derivative gene modified in its 5'ULR by replacing 53 nucleotides immediately upstream of the AUG initiation codon with an 87 nucleotides-long sequence derived from the rolA intron sequence, produce parthenocarpic fruits of high quality. In an in vitro translation system, the iaaM mRNA, modified in its 5'ULR is translated 3-4 times less efficiently than the original transcript. An optimal expressivity of parthenocarpy correlates with a reduced transgene mRNA steady state level in DefH9-RI-iaaM flower buds in comparison to DefH9-iaaM flower buds. Consistent with the known function of the iaaM gene, flower buds transgenic for the DefH9-RI-iaaM gene contain ten times more IAA than control untransformed flower buds, but five times less than DefH9-iaaM flower buds.


CONCLUSIONS
By using an auxin biosynthesis transgene downregulated at the post-transcriptional level, an optimal expressivity of parthenocarpy has been achieved in a genetic background not suitable for the original transgene. Thus, the method allows the generation of a wider range of expressivity of the desired trait in transgenic plants.
Pandolfini
Tiziana
T
Dipartimento Scientifico Tecnologico, University of Verona, Verona, Italy. pandolfini@sci.univr.it
Rotino
Giuseppe L
GL
Camerini
Serena
S
Defez
Roberto
R
Spena
Angelo
A
D020121:5' Untranslated Regions / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics; D035264:Flowers / Q000737:chemistry / Q000196:embryology; D019649:Food Industry / Q000379:methods* / Q000639:trends; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D007210:Indoleacetic Acids / Q000378:metabolism; D007438:Introns / Q000235:genetics; D018551:Solanum lycopersicum / Q000235:genetics*; D006899:Mixed Function Oxygenases / Q000235:genetics; D016296:Mutagenesis / Q000235:genetics; D010312:Parthenogenesis / Q000235:genetics*; D030821:Plants, Genetically Modified / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D011549:Pseudomonas / Q000201:enzymology / Q000235:genetics; D012323:RNA Processing, Post-Transcriptional; D011993:Recombinant Fusion Proteins / Q000235:genetics; D012231:Rhizobium / Q000235:genetics; D019076:Transgenes
D020121:5' Untranslated Regions; D001426:Bacterial Proteins; D007210:Indoleacetic Acids; D011993:Recombinant Fusion Proteins; C096589:rolA protein, Agrobacterium rhizogenes; C030737:indoleacetic acid; D006899:Mixed Function Oxygenases; C023204:tryptophan 2-monooxygenase