Temporal and spatial assessment of defence responses in resistant and susceptible hop cultivars during infection with Verticillium nonalfalfae

Abstract

Hop (Humulus lupulus L.) is an important industrial plant providing ingredients for brewing and pharmaceutical industry worldwide. Its intensive production is challenged by numerous diseases. One of the most lethal and difficult to control is verticillium wilt, a vascular disease caused by the fungal pathogen Verticillium nonalfalfae. The disease can be successfully controlled by the host resistance. Despite various studies that already researched resistance mechanisms of hops, only limited number of resistance genes and markers that could be utilized for efficient resistance breeding has been identified. In this study we aimed to follow fungus colonization pattern and the differential expression of selected genes during pre-symptomatic period of susceptible (Celeia) and resistant (Wye Target) hop cultivars. Results of gene expressions and fungal colonisation of compatible and incompatible interactions with V. nonalfalfae suggest that the hop plant is challenged already at the very early fungal colonisation stages. In total, nine out of 17 gene targets investigated in our study resulted in differential expression between inoculated and control plants of susceptible and resistant cultivars. The difference was the most evident in stems at an early stage of colonisation (6 dpi), showing relatively stronger changes in targeted gene expression to infection in the resistant cultivar than in the susceptible one. Analysed gene targets are involved in the overall defence response processes of nucleic acid binding, signalling, protein ubiquitination, cell oxidative burst, hydroxylation, peroxidation, alternative splicing, and metabolite biosynthesis. The up-regulation of some genes (e.g. glycine-rich RNA-binding family protein, protein phosphatase, cysteine-rich receptor-like protein kinase, zinc finger CCCH domain-containing protein 40, cinnamic acid 4-hydroxylase, class III peroxidase, putative MAPK2, peroxiredoxin-2F) upon infection in incompatible interactions might reflect defence activation, restriction of disease spreading throughout the plant and successful response of resistant genotype.

Keywords: Differential gene expression; Hop; Non-model plants; Verticillium wilt.