Loss of function of thePad-1aminotransferase gene, which is involved in auxin homeostasis, induces parthenocarpy in Solanaceae plants

Abstract

Fruit development normally occurs after pollination and fertilization; however, in parthenocarpic plants, the ovary grows into the fruit without pollination and/or fertilization. Parthenocarpy has been recognized as a highly attractive agronomic trait because it could stabilize fruit yield under unfavorable environmental conditions. Although natural parthenocarpic varieties are useful for breeding Solanaceae plants, their use has been limited, and little is known about their molecular and biochemical mechanisms. Here, we report a parthenocarpic eggplant mutant,pad-1, which accumulates high levels of auxin in the ovaries. Map-based cloning showed that the wild-type (WT)Pad-1gene encoded an aminotransferase with similarity toArabidopsis VAS1gene, which is involved in auxin homeostasis. Recombinant Pad-1 protein catalyzed the conversion of indole-3-pyruvic acid (IPyA) to tryptophan (Trp), which is a reverse reaction of auxin biosynthetic enzymes, tryptophan aminotransferases (TAA1/TARs). The RNA level ofPad-1gene increased during ovary development and reached its highest level at anthesis stage in WT. This suggests that the role ofPad-1in WT unpollinated ovary is to prevent overaccumulation of IAA resulting in precocious fruit-set. Furthermore, suppression of the orthologous genes ofPad-1induced parthenocarpic fruit development in tomato and pepper plants. Our results demonstrated that the use ofpad-1genes would be powerful tools to improve fruit production of Solanaceae plants.