ACC oxidase 발현 억제 식물체에서 폴리아민 생합성 증가에 의한 스트레스 저항성 증강

Enhanced tolerance through increasing polyamine contents in transgenic tobacco plants with antisense expression of ACC oxidase gene

Antisense construct of cDNA for senescence-related ACC oxidase (CAO) cDNA isolated from carnation flowers were introduced into tobacco by Agrobacterium-mediated transformation. The decreasing expression of NtACO and the reduction of ethylene production were observed in these transgenic lines. In contrast, the SAMDC transcripts and spermidine content were increased. The findings that higher content of spermidine in the ethylene suppressed transgenic plants compared with wild-type should be directly resulted in the enhancement of SAMDC activity followed by the increased accumulation of SAMDC transcript. To investigate the pathogenic response in these transgenic plants, wild-type and transgenic plants were inoculated with Phytophthora parasitica pv. nicotianae. Transgenic plants suppressing ethylene production showed the increased resistance against fungal pathogen, comparing with wild-type plant. PR-protein genes expression in CAO-AS-2 and CAO-AS-4 were also higher at the normal growth condition and pathogenic response than in wild-type plants. The results of higher spermidine content and SAMDC activity in transgenic plants, CAO-AS-2 and CAO-AS-4, support the possibility that an increase in spermidine content might induce the higher transcripts of PR-protein genes. This results agreed with the phenomena that spermidine promoted the expression of PR1a and a SAMDC inhibitor, MGBG, decreased the expression of PR1a in leaf discs. These results suggest that the resistance against fungal pathogen in transgenic tobacco impaired in ethylene production might be caused by increasing in polyamine, especially spermidine, biosynthesis.