Genome-wide identification and expression analysis of the melon (Cucumis melo L.) Aux/IAA gene family in response to abiotic and biotic stresses

Cucumis melo L. is an important horticultural crop whose cultivation is limited by environmental stresses. The Auxin/Indole-3-Acetic Acid (Aux/IAA) gene family is central to auxin signaling and plant stress adaptation, yet its functions in melon are unclear. This study identified and characterized the Aux/IAA family in melon to elucidate its roles under stress. Twenty nine CmAux/IAA genes from the melon genome were identified, and phylogenetically classified into eight clades. Collinearity analysis indicated that segmental duplication primarily drove the family's expansion. Promoter analysis revealed cis-regulatory elements linked to development, hormone response, and stress. Transcriptome analysis showed that these genes display characteristic spatiotemporal expression patterns across tissues, and respond differentially to abiotic (salt, drought, chilling, heat, low light), and biotic (downy mildew, powdery mildew, bacterial fruit blotch) stresses. Specifically, CmAux/IAA11 was a core drought-responsive gene; CmAux/IAA26 and 28 were up-regulated under chilling; CmAux/IAA12 and 14 likely function in heat and low light adaptation, respectively. Regarding biotic stress, CmAux/IAA16 responded to downy mildew, CmAux/IAA11 may confer constitutive resistance to powdery mildew, while CmAux/IAA5 and 26 are inducible resistance genes, and elevated expression of CmAux/IAA14, 15, and 26 in susceptible cultivars suggested a negative regulatory role during bacterial fruit blotch. Our findings provide a foundation for functional studies of CmAux/IAA genes, and new insights into melon stress responses.