Advances in Tissue Culture and Regeneration of Canola (<em>Brassica napus</em> L.): Explant Responses, Hormone-Free Shock Treatments, and Emerging Biotechnological Applications

Canola (Brassica napus L.) is a valuable oilseed plant with high agronomic and industrial value globally, but its genetic improvement is typically constrained by low regeneration efficiency and strong genotype dependence. Advances in tissue culture technology have brought new strategies for overcoming such limitations through realization of developmental plasticity of diverse explants and optimization of hormonal regimes. Current studies show that hypocotyls, cotyledons, petioles, roots, and microspores exhibit extremely variable regeneration responses, the best of which are cotyledons in optimized cytokinin–auxin combinations. In addition, transient culture on hormone-free Murashige and Skoog (MS) medium, or a so-called "shock" treatment, has been shown to be a successful technique of endogenous hormone balance resetting, enhancement of rooting, and mimicking natural withdrawal phases favorable for organogenic reprogramming. Mechanistic insight from Arabidopsis thaliana recognizes the epigenetic hurdles, such as Polycomb Repressive Complex 2 (PRC2), to suppress embryogenic competence, while transient exposure to auxin and after hormone withdrawal facilitates transcriptional activation of crucial regulators such as WUSCHEL (WUS), BABY BOOM (BBM), and LEAFY COTYLEDON (LEC). The synthesis of these findings with Brassica tissue culture offers new opportunities for optimization of the regeneration protocol using a mix of hormonal and epigenetic modulation. New biotechnological applications like hairy root transformation, rol gene use, and somatic embryogenesis-mediated induction of metabolites in similar medicinal plants further extend the application of these technologies. Collectively, these advances provide the foundation for improving more efficient regeneration systems in canola, rationalizing transformation pipelines, and enabling new routes to crop modification and metabolic engineering.