Overexpression of apple MdIAA8 in tomato alters plant growth and fruit shape and induces parthenocarpy

AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) proteins are short-lived transcriptional regulators that play central roles in auxin signaling and plant development. However, the function of MdIAA8 in apple ( Malus domestica ) remains poorly understood. In the present study, we identified allele-specific expression (ASE) of MdIAA8 and characterized its expression during apple flower and fruit development. MdIAA8 was expressed at higher levels in balloon stage flowers than in open stage flowers. During early fruit growth, its expression levels in the flesh tissue were elevated compared with those in the skin, core. To investigate its function, MdIAA8 was ectopically expressed in transgenic tomato ( Solanum lycopersicum ). MdIAA8 overexpression reduced plant height, increased root length, altered floral organ development, and induced parthenocarpic fruit set. The transgenic plants also produced smaller fruits with elongated distal tips. Histological analysis revealed that MdIAA8 -overexpressing fruits contained smaller, more densely packed cells than wild-type fruits, indicating reduced cell expansion. Molecular analyses showed altered expression of auxin-responsive genes in the transgenic lines, suggesting that the observed phenotypes are associated with changes in auxin-responsive transcription. Collectively, these findings demonstrate that MdIAA8 influences vegetative and reproductive development and provide new insights into the role of Aux/IAA-mediated auxin signaling in flower and fruit development