Silencing an ACC oxidase gene affects the susceptible host response of Nicotiana benthamiana to infection by Colletotrichum orbiculare

An 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase, NbACO1, was cloned from cDNA of Nicotiana benthamiana leaves infected with the hemibiotrophic fungal pathogen, Colletotrichum orbiculare. Expression of NbACO1 increased approximately 3-fold by 24 h after inoculation and then continued to increase reaching a maximum that was 6-folds greater than that in healthy plants by 96 h after inoculation. A portion of NbACO1 was cloned into a PVX vector for virus-induced gene silencing, and the silencing resulted in a reduction in its expression to 7–9% of that found in the controls for fungal-infected leaf tissue. Silencing of NbACO1 also resulted in significant reductions in transcript levels of genes encoding an ethylene responsive transcription factor and two glutathione S-transferases, but not for a basic pathogenesis-related protein gene, indicating that at least some genes associated with ethylene signaling were affected by the silencing treatment. Inoculated NbACO1-silenced plants developed more lesions more quickly as a result of an accelerated switch from the symptomless, biotrophic phase to the symptomatic necrotrophic phase of infection compared to inoculated control plants. This indicates that manipulation of ACC oxidase can affect the length of the biotrophic phase of infection in this interaction.