Study on Agrobacterium-mediated transient expression in Viola plants

Background: The Viola plants have important value for theoretical and applied research. Agrobacterium-mediated transient expression enables rapid target protein production in plants, yet this system remains poorly established in Viola. Aims: To establish an efficient Agrobacterium-mediated transient expression system in Viola. Methods: By employing two types of A. tumefaciens strains (EHA105 and LBA4404) and green fluorescent protein (GFP) as a reporter, we demonstrated the transient expression in the leaves of four Viola species, including Viola philippica, V. prionantha, V. tricolor, and V. dissecta. Results: GFP transient expression peaked at 4 dpi in all four Viola species. Agrobacterium at OD600 = 0.3 yielded optimal expression, and strain EHA105 was superior to LBA4404; V. philippica showed the highest GFP accumulation. In the optimal system, exogenous indole-3-acetic acid (IAA) improves GFP transient expression with maximum promotion at 50 ng/mL, while methyl jasmonate (MeJA) has no facilitating effect. This system enables transient expression of FMDV VP1, whose expression is also markedly increased by 50 ng/mL IAA. Conclusions: This study successfully established a transient expression system for Viola and identified factors affecting Agrobacterium-mediated transient expression efficiency in this genus.