# Phenylpropanoid metabolites from grape leaves contribute to strong defense roles against downy mildew based on physiological and transcriptomic analyses

## TL;DR

This study shows that grape leaves with higher levels of phenylpropanoid metabolites are more resistant to downy mildew, a serious grape disease.

## Contribution

The study identifies specific genes and metabolites in grape leaves linked to resistance against downy mildew using transcriptomic and physiological analyses.

## Key findings

- Moldova grape leaves showed higher resistance to downy mildew compared to Red Globe.
- Moldova had higher levels of lignin, total phenols, and flavonoids, contributing to its resistance.
- Transcriptomic analysis revealed that Moldova activated more disease-resistant genes in the phenylpropanoid pathway.

## Abstract

Downy mildew caused by Plasmopara viticola seriously affects global grape production. In this study, the cultivars of Moldova and Red Globe were inoculated with Plasmopara viticola separately. The results showed that the inoculated sites on Red Globe leaves were densely covered with white cotton-like mycelial mats, whereas sparse white mycelia were observed on Moldova leaves. Disease index analysis of Moldova and Red Globe after inoculation with the pathogen showed that Red Globe had a much higher disease index than Moldova, indicating that Red Globe was a highly resistant cultivar, while Moldova was a susceptible cultivar. Furthermore, it was discovered that Moldova had significantly higher contents of lignin, total phenols, and flavonoids than Red Globe. Moreover, RNA-seq technology was used to analyze transcriptomic changes in Red Globe and Moldova after inoculation at 1 dpi and 5 dpi separately. Combined with GO and KEGG databases to annotate differentially expressed genes (DEGs), the DEGs related to the plant hormone signal transduction pathway (VvPR1, VvJAR1, VvSUC11, etc.), phenylpropanoid metabolism (VvCAD, VvCCoAOMT, etc.), flavonoid biosynthesis pathways (VvCHS, VvF3H, VvDFR, etc.), and the stilbenoid, diarylheptanoid, and gingerol biosynthesis pathway (VvROMT, VvSTSs) were further analyzed. Furthermore, the results showed that Moldova activated more disease-resistant genes in the phenylpropanoid metabolic pathway, and the expression levels of genes related to disease-resistant pathways were significantly higher than those in Red Globe. This study lays a foundation for screening candidate target genes for downy mildew-resistant grape breeding and for analyzing the interaction mechanism between the pathogen and grapes.