Early transcriptional responses associated with downy mildew resistance in grapevine

Abstract

Downy mildew caused by Plasmopara viticola remains a central challenge in grapevine production, particularly under conditions aiming at reduced fungicide input. For this reason, breeding strategies increasingly focus on resistance loci (Rpv) derived from wild Vitis species. Although these loci are widely used in modern breeding programmes, the early molecular processes underlying their resistance response are still not fully clarified.

In this work, we examined transcriptional responses following infection with P. viticola in grapevine cultivars differing clearly in their resistance background. Leaf disc assays were performed using Grüner Veltliner as a susceptible Vitis vinifera cultivar and Seyval blanc as a genotype with established Rpv-mediated resistance. Samples were collected at early time points after inoculation and analysed by RNA sequencing.

After pathogen exposure, Seyval blanc displayed marked and rapid changes in gene expression. Grüner Veltliner, in contrast, reacted only weakly. Moreover, a considerable number of genes showed opposing regulation patterns between the two cultivars. Defence-associated transcripts, including genes related to stress signalling, reactive oxygen species metabolism and pathogenesis-related proteins, were strongly induced in the resistant genotype. In particular, numerous RPP13-like disease resistance transcripts were differentially regulated, often with opposing expression trends between cultivars, suggesting genotype-specific modulation of NLR-associated defence components.

In parallel, a subset of transcripts associated with chloroplast function and primary carbohydrate metabolism showed reduced expression or opposing trends in Grüner Veltliner relative to the resistant genotype, consistent with an early separation of basal metabolic adjustment and defence-related transcriptional activation.

Altogether, the data indicate that Rpv-mediated resistance is accompanied by an early and coordinated transcriptional adjustment. The candidate genes identified here will be further analysed by qRT-PCR and may support ongoing efforts to functionally characterise resistance loci relevant for grapevine breeding.