Genome-Wide Identification and Expression Profiling of the Aux/IAA Gene Family in Eggplant (Solanum melongena L.) Reveals Its Roles in Abiotic Stress and Auxin Responses

The auxin/indole-3-acetic acid (<i>Aux</i>/<i>IAA</i>) gene family encodes central regulators of plant development and stress adaptation. Eggplant (<i>Solanum melongena</i>), an economically important vegetable crop, is highly susceptible to abiotic stresses, yet its <i>Aux</i>/<i>IAA</i> family remains uncharacterized. This study aimed to systematically characterize the <i>Aux</i>/<i>IAA</i> gene family in eggplant and to explore its potential roles in development and abiotic stress responses using a genome-wide approach. Here, <i>35 SmIAA</i> genes were identified through comprehensive bioinformatic analyses, including phylogenetic classification, synteny analysis, protein-protein interaction prediction, and qRT-PCR validation. Phylogenetic analysis classified these genes into Clades A and B, encompassing nine subgroups, with subgroup B4 showing lineage-specific expansion and encoding non-canonical <i>Aux</i>/<i>IAA</i> proteins. Expression profiling revealed that <i>SmIAA18</i> and <i>SmIAA33</i> were strongly responsive to salt stress, whereas <i>SmIAA1</i>/<i>2</i>/<i>8</i> were preferentially induced by drought stress. Furthermore, <i>SmIAA8</i> and <i>SmIAA33</i> exhibited contrasting responses to IAA treatment, characterized by delayed induction and rapid repression, respectively. This study presents the first genome-wide analysis of the <i>Aux</i>/<i>IAA</i> family in eggplant, elucidating its roles in development and stress adaptation, and provides valuable genetic resources for the molecular breeding of stress-tolerant varieties.