Genome-wide characterization of the expansin gene family in Sorghum bicolor reveals their regulatory features and roles in drought response

Abstract

Expansins (EXPs) are non-enzymatic proteins that mediate cell wall loosening and play essential roles in plant growth, development, and stress responses. However, the expansin gene family in Sorghum bicolor remains insufficiently characterized. In this study, we identified 68 expansin genes in S. bicolor (SbEXPs), predominantly belonging to the EXPA and EXPB subfamilies. Structural and evolutionary characterization revealed conserved domain organization, with gene family expansion likely driven by tandem and segmental duplications. Regulatory analysis revealed diverse cis-regulatory elements and predicted interactions with transcription factors, miRNAs, and protein-protein interaction partners, indicating multi-layered regulatory control. Network analysis further identified key genes, including SbEXPA17, SbEXPB1, and SbEXPB2, as potential central nodes. Expression profiling demonstrated distinct tissue-specific patterns, with many SbEXP genes highly expressed in roots and other actively growing tissues. Under drought conditions, RNA-seq data revealed differential expression of several SbEXP genes, with a subset consistently upregulated. These patterns were validated by qRT-PCR, confirming strong induction of genes such as SbEXPA17, SbEXPB6, and SbEXPB8 under PEG-simulated drought stress. This study provides a comprehensive characterization of the expansin gene family in S. bicolor and suggests their potential involvement in drought response through modulation of cell wall dynamics. These findings offer a foundation for future functional studies and the development of drought-resilient sorghum varieties.