Solanum sisymbriifolium plants become more recalcitrant to Agrobacterium transfection as they age

Abstract Solanum sisymbriifolium is representative of some undomesticated plant species that appear to be recalcitrant to Agrobacterium -mediated infection. Transient expression assays in this weed using β-glucuronidase (GUS) expression have proven highly variable and often failed. Systematic optimization experiments revealed that reducing wounding when bacteria were applied reduced variability. Transfection levels were also influenced by the number of leaves infected/plant, and by total leaves at the time of infection. This inverse relationship between leaf number and GUS expression resembled age-related resistance, but did not correlate with flowering, the accumulation of salicylic acid during bacterial infection, or with overt signs of senescence.