Priming of flax by a non-pathogenic Fusarium oxysporum involves local and systemic reductions in putrescine levels

The non-pathogenic strain of Fusarium oxysporum appears to be a very good priming agent, as by colonizing flax plants, it significantly limits the spread of the pathogenic strain of F. oxysporum (Foln), which is responsible for the most dangerous flax disease, Fusarium wilt. The priming mechanism involves local and systemic activation of pathogenesis-related genes and systemic activation of the antioxidant system, but whether this might be polyamine-dependent has not yet been determined. Therefore, our goal was to determine the role of polyamines in this mechanism. We demonstrated that treatment of flax plants with the endophytic F. oxysporum Fo47 strain resulted in a significant reduction in putrescine content. To confirm the importance of this polyamine in priming, we treated flax plants with putrescine and then infected them with Foln. We demonstrated that a constantly elevated putrescine content in the plants actually promoted infection. We then infected flax plants previously primed with Fo47 and those co-treated with Fo47 and Foln. We observed an increase in transcripts of the adc , odc , and dao genes in the initial days of infection, and a decrease in putrescine levels in the roots and shoots of plants primed with Fo47 compared to plants infected only with Foln and plants co-treated with Fo47 and Foln. In later days of infection, a significantly greater increase in transcripts of polyamine metabolism genes was observed in plants infected only with Foln, indicating significant progression of infection. In summary, the reduction in putrescine levels in plants is an important element of the priming process.