Cysteine proteinases of Nicotiana benthamiana after inoculation with Colletotrichum destructivum or Pseudomonas syringae
Two papain family cysteine proteinase genes, 'NbCYP1' and 'NbCYP2', and a metacaspase type II gene, 'NbMCA1 ', were amplified from cDNA off. benthamiana infected with ' C. destructivum'. All three showed peak expression corresponding with the switch to necrotrophy by 'C. destructivum'. After inoculation with the incompatible bacterium, 'P. syringae' pv. ' tomato, NbCYP2' and 'NbMCA1' expression at 3 hours post inoculation increased, whereas expression of 'NbCYP1' decreased. Expression of all three then returned to near pre-inoculation levels and remained constant as necrosis later appeared due to a non-host hypersensitive response (HR). Virus-induced gene silencing of 'NbCYP1, NbCYP2' and 'NbMCA1' resulted in increased susceptibility of ' N. benthamiana' to 'C. destructivum' but did not affect HR necrosis or population levels of 'P. syringae' pv. ' tomato'. These cysteine protenase genes do not appear to be involved in the programmed cell death of HR resistance to 'P. syringae' but may limit the susceptibility to 'C. destructivum'.