Pseudomonas fluorescens PTA-CT2 Triggers Local and Systemic Immune Response Against Botrytis cinerea in Grapevine

Although induced systemic resistance (ISR) is well-documented in the context of plant-beneficial bacteria interactions, knowledge about the local and systemic molecular and biochemical defense responses before or upon pathogen infection in grapevine is very scarce. In this study, we first investigated the capacity of grapevine plants to express immune responses at both above- and below-ground levels upon interaction with a beneficial bacterium, Pseudomonas fluorescens PTA-CT2. We then explored whether the extent of priming state could contribute to the PTA-CT2-induced ISR in Botrytis cinerea-infected leaves. Our data provide evidence that this bacterium colonized grapevine roots but not the above-ground plant parts and altered the plant phenotype that displayed multiple defense responses both locally and systemically. The grapevine roots and leaves exhibited distinct patterns of defense-related gene expression during root colonization by PTA-CT2. Roots responded faster than leaves and some responses were more strongly upregulated in roots than in leaves and vice versa for other genes. These responses appear to be associated with some induction of cell death in roots and a transient expression of HSR, a hypersensitive response-related gene in both local (roots) and systemic (leaves) tissues. However, stilbenic phytoalexin patterns followed opposite trends in roots compared with leaves but no phytoalexin was exuded during plant-bacterium interaction, suggesting that roots could play an important role in the transfer of metabolites contributing to immune response at the systemic level. Unexpectedly, in B. cinerea-infected leaves PTA-CT2-mediated ISR was accompanied in large part by a downregulation of different defense-related genes, including HSR. Only phytoalexins and glutathion-S-transferase 1 transcripts were upregulated, while the expression of anthocyanin biosynthetic genes was maintained at a higher level than the control. This suggests that decreased expression of HSR, as a marker of cell death, and activation of secondary metabolism pathways could be responsible for a reduced B. cinerea colonization capacity in bacterized plants.