Trichome formation in Nicotiana benthamiana is induced by certain Agrobacterium tumefaciens strains

Plant trichomes are specialized epidermal appendages found on various organs of many plant species. They protect against abiotic and biotic stresses, and agricultural, medicinal, and industrial products are derived from them. Here, we show that infiltration of Nicotiana benthamiana leaf tissue with certain commonly used laboratory nopaline-type Agrobacterium tumefaciens strains induces a greater than six-fold increase, localized formation of glandular trichomes 15 days post-infiltration. This effect is Agrobacterium strain-specific and is caused by a trans-zeatin synthase gene, tzs, located on Ti plasmids of trichome-inducing strains. Transfer of tzs to strains incapable of trichome induction causes similar trichome production upon leaf infiltration. The tzs gene facilitates Agrobacterium production of the cytokinin zeatin, and similar trichome induction occurs when leaves are infiltrated with either zeatin or the related cytokinin 6-benzylaminopurine. This simple procedure enables dramatically increased trichome density to be compared biologically between adjacent isogenic plant tissues on the same leaf. Using this assay, increased trichome densities on N. benthamiana leaves are shown to reduce leaf predation by Helicoverpa armigera larvae. Finally, the cytokinin response produced by some, but not all, laboratory strains of Agrobacterium need to be considered when interpreting transient expression assay results.