ANNOUNCEMENTS
Polyploid Brassica species constitute a globally relevant commercial crop. However, they are highly vulnerable to terminal heat stress, which adversely affects reproductive stages resulting in significant yield losses. Induction of early flowering is a proven strategy to evade such stress and the central floral integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) presents a promising target to achieve it. However, in polyploid B. juncea, elucidation of SOC1 regulation is complicated by extensive gene duplication and regulatory redundancy, leading to multiple homeologs of SOC1 promoter and upstream regulators that generate complex combinatorial interactions. This thesis investigates the regulatory architecture of SOC1 in B. juncea, focusing on functional diversification of SOC1 promoter homeologs and TF interaction dynamics. Complementation analysis in the Arabidopsis thaliana soc1-2 mutant background revealed significant variation in promoter homeolog strengths, with the AAMF2 promoter driving elevated SOC1 expression and significantly earlier flowering compared to AALF, identifying AAMF2 as a dominant regulatory element. To address polyploidy-driven regulatory complexity, an integrative in silico framework combining molecular docking and molecular dynamics (MD) simulations was employed to evaluate interactions between homologs of SOC1 promoter and key upstream TFs viz. SVP, FUL, CCA1, and SOC1 itself. Despite sequence-based structural divergence, promoter-TF complexes exhibited comparable binding affinities maintained through compensatory mutations, which were validated via yeast one-hybrid assays. MD simulations highlighted the stabilizing contribution of non-canonical TF domains and promoter flanking sequences. Atomic-level analysis identified critical amino acid and nucleotide interaction hotspots. Overall, this work advances understanding of SOC1 regulation in polyploid B. juncea and provides a rational framework for synthetic promoter design, precision genome editing, and development of early-flowering, climate-resilient Brassica cultivars.
