Developmental regulation of lupulin gland-associated genes in aromatic and bitter hops (Humulus lupulus L.)

Abstract

Background Hop (Humulus lupulus L.) bitter acids are valuable metabolites for the brewing industry. They are biosynthesized and accumulate in glandular trichomes of the female inflorescence (hop cone). The content of alpha bitter acids, such as humulones, in hop cones can differentiate aromatic from bitter hop cultivars. These contents are subject to genetic and environmental control but significantly correlate with the number and size of glandular trichomes (lupulin glands). Results We evaluated the expression levels of 37 genes involved in bitter acid biosynthesis and morphological and developmental differentiation of glandular trichomes to identify key regulatory factors involved in bitter acid content differences. For bitter acid biosynthesis genes, upregulation of humulone synthase genes, which are important for the biosynthesis of alpha bitter acids in lupulin glands, could explain the higher accumulation of alpha bitter acids in bitter hops. Several transcription factors, including HlETC1, HlMYB61 and HlMYB5 from the MYB family, as well as HlGLABRA2, HlCYCB2–4, HlZFP8 and HlYABBY1, were also more highly expressed in the bitter hop cultivars; therefore, these factors may be important for the higher density of lupulin glands also seen in the bitter hop cultivars. Conclusions Gene expression analyses enabled us to investigate the differences between aromatic and bitter hops. This study confirmed that the bitter acid content in glandular trichomes (lupulin glands) is dependent on the last step of alpha bitter acid biosynthesis and glandular trichome density.

The Splicing Variant TFIIIA-7ZF of Viroid-Modulated Transcription Factor IIIA Causes Physiological Irregularities in Transgenic Tobacco and Transient Somatic Depression of “Degradome” Characteristic for Developing Pollen

“…It is not known in this respect, whether an involvement of TFIIIA-7ZF in viroid propagation/pathogenesis and plant morphogenesis represents a more general phenomenon. At least, a recent report about its potential role in hop latent viroid-infected hop [ 43 ] and our unpublished results about some morphological changes mediated by hop-specific Hl TFIIIA-7ZF in tobacco should support further physiological studies of this factor.…”

“Pathomorphogenic” Changes Caused by Citrus Bark Cracking Viroid and Transcription Factor TFIIIA-7ZF Variants Support Viroid Propagation in Tobacco

“…The symptoms' expressions are obviously caused by part of a CBCVdinduced pathogenesis network [8,[10][11][12]. The modification of TFIIIA factor(s) in hops obviously play a significant role in the propagation of hop viroids, as indicated for HLVd by Patzak et al [18]. While CBCVd causes severe pathogenesis in hops, there are negligible symptoms caused by CBCVd infection in N. tabacum and the infection proceeds rather in a latent form, as judged by visible symptoms in somatic tissues.…”

“…The sequence NbTFIIIA-7ZF was cloned previously [13] from N. benthamiana infected with the lethal strain of PSTVd (AS1) [63]. HlTFIIIA-7ZF was amplified by RT-PCR from hops (Humulus lupulus clone Osvald's 72) naturally infected with HLVd [18,64] using primers HlTFIIIA7start and TFIIIAstop (Table S1). The fragment was re-amplified by Pwo polymerase and the blunt-end was cloned into pPCR-Script Amp SK(+) (Stratagene).…”