The DefH9-iaaM auxin-sinthesizing gene increases plant fecundity and fruit production in strawberry and raspberry

Background: The DefH9-iaaM gene fusion which is expressed specifically in placenta/ovules andpromotes auxin-synthesis confers parthenocarpic fruit development to eggplant, tomato andtobacco. Transgenic DefH9-iaaM eggplants and tomatoes show increased fruit production duemainly to an improved fruit set. However, the weight of the fruits is also frequently increased.Results: DefH9-iaaM strawberry and raspberry plants grown under standard cultivation conditionsshow a significant increase in fruit number and size and fruit yield. In all three Rosaceae speciestested, Fragaria vesca, Fragaria x ananassa and Rubus idaeus, DefH9-iaaM plants have an increasednumber of flowers per inflorescence and an increased number of inflorescences per plant. Thisresults in an increased number of fruits per plant. Moreover, the weight and size of transgenic fruitswas also increased. The increase in fruit yield was approximately 180% in cultivated strawberry,140% in wild strawberry, and 100% in raspberry. The DefH9-iaaM gene is expressed in the flowerbuds of all three species. The total IAA (auxin) content of young flower buds of strawberry andraspberry expressing the DefH9-iaaM gene is increased in comparison to untransformed flowerbuds. The DefH9-iaaM gene promotes parthenocarpy in emasculated flowers of both strawberryand raspberry.Conclusions: The DefH9-iaaM gene is expressed and biologically active in Rosaceae. The DefH9-iaaM gene can be used, under cultivation conditions that allow pollination and fertilization, toincrease fruit productivity significantly in Rosaceae species. The finding that the DefH9-iaaM auxinsynthesizinggene increases the number of inflorescences per plant and the number of flowers perinflorescence indicates that auxin plays a role in plant fecundity in these three perennial Rosaceaespecies