Genetic engineering of parthenocarpic tomato plants using transient SlIAA9 knockdown by novel tissue-specific promoters.

Parthenocarpy is the development of an ovary into a seedless fruit without pollination. The ubiquitous downregulation of SlIAA9 induces not only parthenocarpic fruit formation but also an abnormal vegetative phenotype. To make parthenocarpic transgenic tomato plants without unwanted phenotypes, we found two genes, namely, Solyc03g007780 and Solyc02g067760, expressed in ovary tissue but not in vegetative tissues. Solyc03g007780 was expressed in developing ovaries and anthers. Solyc02g067760 mRNA was detected in whole-flower tissues. The promoters of Solyc03g007780 (Psol80) and Solyc02g067760 (Psol60) predominantly induced the expression of genes in the ovule, placenta, endocarp and pollen and in whole-flower tissues, respectively. Psol80/60-SlIAA9i lines, created for SlIAA9-RNA interference controlled by two promoters, successfully formed parthenocarpic fruits without pleiotropic effects in vegetative tissues. Downregulation of SlIAA9, responsible for parthenocarpic fruit formation, was observed in ovules rather than ovaries in the Psol80/60-SlIAA9i lines. Although the weight of parthenocarpic fruits of the Psol80/60-SlIAA9i lines was lower than the weight of pollinated fruits of the wild type (WT), the parthenocarpic fruits presented redder and more saturated colors and higher levels of total soluble solids and titratable acidity than the WT fruits.