Viroids are small infectious pathogens, composed of a short single-stranded
circular RNA. Hop (Humulus lupulus L.) plants are hosts to four viroids from the family Pospiviroidae. Hop latent viroid (HLVd) is spread worldwide in all hop-growing regions without any visible symptoms on infected hop plants. In this study, we evaluated the influence of HLVd
infection on the content and the composition of secondary metabolites in maturated hop cones, together with gene expression analyses of involved biosynthesis and regulation genes for Saaz, Sládek, Premiant and Agnus cultivars. We confirmed that the contents of alpha bitter
acids were significantly reduced in the range from 8.8% to 34% by viroid
infection. New, we found that viroid
infection significantly reduced the contents of
xanthohumol in the range from 3.9% to 23.5%. In
essential oils of Saaz cultivar, the contents of
monoterpenes,
terpene epoxides and
terpene alcohols were increased, but the contents of
sesquiterpenes and
terpene ketones were decreased. Secondary metabolites changes were supported by gene expression analyses, except
essential oils. Last-step biosynthesis
enzyme genes, namely
humulone synthase 1 (HS1) and 2 (HS2) for alpha bitter
acids and O-methytransferase 1 (OMT1) for
xanthohumol, were down-regulated by viroid
infection. We found that the expression of
ribosomal protein L5 (RPL5) RPL5 and the splicing of
transcription factor IIIA-7ZF were affected by viroid
infection and a disbalance in proteosynthesis can influence transcriptions of biosynthesis and regulatory genes involved in of secondary metabolites biosynthesis. We suppose that RPL5/
TFIIIA-7ZF regulatory cascade can be involved in HLVd replication as for other viroids of the family Pospiviroidae.