Characterization of Hops (H. lupulus) Mildew Infection using Transcriptomics
Authors: Reinartz Dakota M. , Wolyniak Michael J. 
Published: June 2021

Humulus lupulus, commonly known as the common hop, is a twining vine in the Cannabaceae family that produces a flower, or cone, primarily used in the manufacture of beer. H. lupulus, like other plants, suffers from pathogenic infection. Two of the most devastating fungal infections in hop plants are downy and powdery mildew. Powdery mildew is caused by the fungus Podosphaera macularis and downy mildew by the fungus Pseudoperonospora humuli. These two pathogens can rapidly infect an entire commercial hops crop and can cost commercial producers a significant amount of money. These pathogens are fairly well characterized, but the currently known antifungal treatments available have mixed results in saving hops crops. Comparatively little is known about the effect these pathogens have on H. lupulus at the molecular level. Understanding these pathogens' effect on H. lupulus at the molecular level could give us information on how to better treat infected plants or even generate resistant hop strains.

In this project, we are seeking to characterize a hop mildew infection utilizing transcriptomics. Current work focuses on the reliable identification of hop plants suspected to be infected with downy or powdery mildew using molecular tools. Specifically, we are utilizing primers targeted to the rDNA of these fungal pathogens to perform PCR on genomic DNA samples from combined plant/fungus extracts. We have found that in our plant samples the primer set designed to amplify rDNA specific to P. macularis produces two unique bands at 800 and 1200 basepairs. While these bands are different from those predicted based on previous literature (Patzak 2005), they are consistent and replicable across several candidate infected plants. These bands are currently being excised and purified to be sequenced to provide additional information with respect to the specifcity of these PCR results for P. macularis identification. We have been thus far unable to generate reliable molecular markers for the identification of P. humuli.

Once an infected plant has been identified by molecular means, the total RNA from the plant is extracted and reverse transcribed to cDNA. This cDNA is then sent off to be sequenced. In our results, we are looking for increases in the expression of genes related to the plant's defense response similar to A. thaliana genes previoulsy implicated in such a response, including PAD4, EDS1, and PR1 (Howard et al., 2013). We also seek transcripts from the mildews that are expressed in the infected samples that are correlated with poor outcomes for H. lupulus viability. We may also learn about some alternative splicing events that were previously unknown in hops (Howard et al., 2013). Genes of interest or genes that are expressed at an abnormal level will be further investigated to better understand their function with respect to pathogenesis and defense. Overall, this research will reveal new perspectives on the pathogenic fungi's effect on hops at a molecular level and how we may be able to combat the fungi in a novel way by understanding their transcriptomes.

This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.