An Efficient Regeneration and Transient Transformation System for the Desert Halophyte Halostachys caspica.

Halostachys caspica is a salt-tolerant shrub widely distributed on saline-alkali soils in Xinjiang, but research on its salt-tolerance mechanisms has been limited by the lack of reliable regeneration and transformation protocols. We optimized seed germination on 1/2 MS medium with 45 g/L sucrose, significantly raising rates from 8.7% to 70.3% and providing adequate explant material. For regeneration, we developed two complementary protocols: a conventional route using seedling-derived assimilation branches, with optimal adventitious bud induction on medium containing 100 mM NaCl and 1 mg/L 6-BA, followed by transfer to proliferation medium (100 mM NaCl, 0.8 mg/L 6-BA, 0.5 mg/L IBA) that resulted in simultaneous proliferation, elongation, and rooting; and an accelerated protocol using regenerated plantlet assimilation branches, which produced complete plantlets within 35 days on medium with 1 mg/L IBA and 100 mM NaCl, establishing an effective rapid propagation system. Using these explants, we optimized Agrobacterium-mediated transformation parameters, achieving over 90% transient transformation efficiency. Together, this regeneration and transformation platform will facilitate functional dissection of stress-responsive genes and regulatory networks, while the rapid propagation protocol provides reliable planting material and may serve as a reference for other woody plants and halophytes lacking established regeneration systems.