Pangenome-Wide Identification, Evolutionary Characterisation and Stress- Responsive Dynamics of SIZ1-Type SUMO E3 Ligase Gene Family in Bread Wheat (Triticum aestivum L.)

Background: SUMOylation, a key post-translational modification in plants, modulates diverse stress responses through SUMO E3 ligases (SIZ1). The SIZ1 gene family remains uncharacterized in bread wheat ( Triticum aestivum L.), despite its proven functional relevance in model systems. Results: The pangenome survey of bread wheat identified 15 TaSIZ1 genes, unevenly distributed across the genomes. The reference genome Chinese Spring harboured 14 TaSIZ1 genes distributed across homoeologous groups 1, 3, 4, 5, and 7. These intron-rich TaSIZ1 genes with 14–17 exons encode nuclear-localised, hydrophilic SIZ proteins (pI 4.85–6.60) that carry a conserved zf-MIZ1 domain. The TaSIZ1 family expansion occurred predominantly through whole-genome and segmental duplications under purifying selection (Ka/Ks < 1). The synteny and orthology among wheat, barley, rice, maize, and sorghum SIZ1 genes further confirmed evolutionary conservation, with strong purifying selection (Ka/Ks: 0.21–0.46). Promoter analysis revealed abundant stress- and hormone-responsive cis-elements (ABRE, MBS, ARE, GT1), alongside major transcription factor binding sites for ERF, WRKY, MIKC_MADS, and MYB families. Expression profiling showed higher basal activity of TaSIZ1-1A, 1B, 1D, 3B, and 3D in vegetative tissues and induction by heat, drought, powdery mildew, and leaf rust. Conclusions: Our study showed that TaSIZ1 genes are structurally conserved but show functional divergence across homoeologs and genotypes. The strong, specific induction of selected copies underscores their utility in enhancing stress resilience. This study provides the first comprehensive framework for understanding TaSIZ1 regulation in wheat and nominates candidate genes for multi-stress engineering and wheat breeding.