Genome-Wide Identification and Stress-Responsive Expression Analysis of the AUX/IAA Gene Family in Sorghum

Sorghum (Sorghum bicolor), a drought- and salt-tolerant staple cereal, supports over 500 million people globally as food, fiber, and fuel. Auxin/Indole-3-Acetic Acid (Aux/IAA) proteins regulate auxin signaling for plant growth and stress responses. However, the Aux/IAA gene family in sorghum has not yet been comprehensively analyzed. In this study, a total of 42 SbAUX genes were identified, and phylogenetic analysis revealed that the SbAUXs could be clustered into five subfamilies. Structural analysis further revealed that these subfamilies exhibit distinct structural features, while structures remain relatively conserved within each subfamily. The expansion of SbAUX genes has been mediated by multiple duplication types, with whole-genome duplication (WGD) events identified as the predominant driving force. Interspecific collinearity analysis revealed that AUX genes have undergone purifying selection. Promoter analysis revealed that the SbAUX gene promoters contain stress-responsive elements including as-1 and STRE, and transcriptome analysis combined with RT-qPCR data implied a potential involvement of SbAUX genes in the response to salt and PEG stresses. These findings provide a preliminary theoretical basis for exploring sorghum’s molecular responses to stress, and the SbAUX genes identified herein might represent potential candidate genes for genetic improvement in sorghum.