Comparative genomics and stress-responsive expression of the IMP gene family in Sorghum bicolor

Inositol monophosphatase (IMP) is a key enzyme in the inositol signaling pathway and ascorbic acid (AsA) biosynthesis, playing crucial roles in plant growth, development, and abiotic stress responses. Sorghum (S. bicolor) is an important cereal crop with remarkable drought and salinity tolerance, yet a systematic analysis of the IMP gene family in sorghum has been lacking. In this study, we identified eight IMP genes (SbIMP-1-SbIMP-8) in the sorghum genome. Phylogenetic analysis classified them into six subfamilies, consistent with rice and maize, suggesting a common ancestral origin. Gene structure and motif composition were highly conserved within each subfamily but varied among subfamilies, indicating functional divergence. Synteny analysis revealed strong collinearity between sorghum and maize with mostly one-to-one orthologous relationships, whereas complex one-to-many correspondences were observed with the polyploid S. spontaneum, highlighting lineage-specific expansion driven by whole-genome duplication. Promoter cis-element analysis identified numerous stress-related and hormone-responsive elements, including ABRE, DRE, MYB and MYC binding sites. Transcriptome and qRT-PCR analyses under salt (NaCl) and osmotic (PEG) stresses revealed distinct expression patterns: SbIMP-1, SbIMP-3, SbIMP-6, SbIMP-7 and SbIMP-8 acted as salt responders. In particular, SbIMP-4 exhibited a strong salt-specific induction. Promoter enrichment of MYB and MYC binding sites was associated with rapid salt response, whereas the combination of DRE, ABRE and MYB sites in SbIMP-4 likely underpinned its unique expression profile. This study provides preliminary insights into the expression profiles of SbIMP genes under salt and osmotic stresses, offering a theoretical foundation for molecular breeding aimed at improving abiotic stress response in sorghum and other crops.