Genome-Wide Identification of SGR and SGRL Gene Family Members in Thirteen Species and their Expression Under Drought Stress in Sorghum bicolor Seedlings

Abstract Leaf senescence is a genetically programmed developmental process essential for nutrient remobilization and adaptation to environmental stresses. The SGR and SGRL gene families play pivotal roles in regulating chlorophyll degradation pathways. This study presents a genome-wide analysis of SGR and SGRL genes across 13 species from monocot and dicot. We identified 23 SGR and 17 SGRL genes encoding 31 and 28 proteins, respectively. Phylogenetic analysis classified these proteins into two groups and four subgroups, revealing evolutionary relationships consistent with speciation events. Intron-exon structural analyses highlighted conserved structures within subgroups. Subcellular localization predictions indicate plastid targeting, with SGRs associated with thylakoid membranes and SGRLs localizing predominantly to the chloroplast envelope, suggesting distinct functional niches within the chloroplast. Regulatory analyses uncovered 1,661 cis -acting elements encompassing stress-, light-, and hormone-responses, notably abundant abscisic acid-responsive elements. Post-transcriptional control is evident through miRNA families such as miR164 and miR159, underscoring multilayered regulation. Functional network analysis revealed overlapping interactomes for SbSGR and SbSGRL involving key chlorophyll metabolic enzymes, while differential expression profiling under drought stress in Sorghum cultivars ‘Kimia’ (drought-resistant) and ‘Sepideh’ (drought-sensitive) uncovered cultivar-specific patterns: rapid SbSGR repression with transient SbSGRL induction in Kimia, versus gradual SbSGR decline and sustained SbSGRL upregulation in Sepideh. Overall, SGR and SGRL genes exhibit profound evolutionary divergence and intricate spatial, regulatory, and functional specialization. Their coordinated but distinct roles facilitate chlorophyll catabolism and senescence, enabling plants to fine-tune developmental and stress responses. This framework supports future validation and biotechnological strategies to improve crop resilience under abiotic stress.