Comparison of PR1 expression in grapevine cultures after inoculation with a host- and a non-host pathogen

Abstract

PR1 gene induction was monitored by RT-PCR in three different grapevine cultures that were inoculated with Plasmopara viticola as a host pathogen and Pseudoperonospora cubensis as a non-host pathogen. The results of the expression analysis showed that the PR1 mRNA level in Vitis vinifera cv. Riesling and Vitis riparia cv. Gloire de Montpellier is mainly affected by the culture system. PR1 is constitutively expressed in callus cultures. In vitro plants showed a low basal expression of PR1 that is enhanced after challenge with both downy mildews in the two species tested. In greenhouse plants, PR1 is only expressed 24 h post inoculation (hpi) but not 12 hpi. Heavily infected leaves (‘oilspots‘) of the susceptible cv. Riesling, exhibiting well developed infection structures in the intercellular space as indicated by microscopical methods, also showed a high PR1 expression rate three weeks post inoculation. Thus, the role of PR1 expression in impeding the downy mildew pathogen remains equivocal. It seems that expression of PR1 is a general stress response in some grapevine culture systems and that their use as a reference for gene expression analysis is limited.