Tissue-specific transcriptomic dynamics under drought stress in domesticated sorghum, <i>S. bicolor</i>

Abstract Drought is a critical issue for global agriculture making the development of drought-resilient crop varieties crucial . Sorghum bicolor (L.) Moench is a highly drought tolerant cereal crop with the potential to serve as a model for identifying drought-tolerant genes. Investigating drought-induced gene expression changes in S. bicolor can inform breeding strategies aimed at enhancing resilience in other crops in the Poaceae family. Our aim was to identify the genes and networks that are differentially expressed in drought stressed sorghum across multiple tissue types, not just leaves. Previously, we reported differences in phenotype in terms of biomass, photosynthetic traits and the concentration of specialized metabolites (dhurrin and phenolics) between well-watered and water-limited plants. Here, differential gene expression analysis was conducted for drought-stressed S. bicolor variety BTx623 using edgeR. Gene ontology enrichment analysis and Weighted Gene Correlation Network Analysis (WGCNA) were conducted to identify the over-represented functions of the differentially expressed genes and to identify clusters of genes that behave together as a response to drought, respectively. Gene expression changes were largely confined to the root (56 genes were found to be differentially expressed), with little differential expression in the leaves or sheaths and no significant differences in expression of key dhurrin pathway genes. Together, these results indicate that drought tolerance in the cultivated sorghum reference genotype BTx623 is associated primarily with root-specific transcriptional responses and provide a tissue-resolved baseline for future comparative analyses across sorghum genotypes and wild relatives differing in drought sensitivity and HCN potential.