Elena L. Peredo

Genetic and epigenetic stability of cryopreserved and cold-stored hops (Humulus lupulus L.)

Conventional cold storage and cryopreservation methods for hops (Humulus lupulus L.) are available but, to our knowledge, the genetic and epigenetic stability of the recovered plants have not been tested. This study analyzed 51 accessions of hop using the molecular techniques, Random Amplified DNA Polymorphism (RAPD) and Amplified Fragment Length Polymorphism (AFLP), revealing no genetic variation among greenhouse-grown controls and cold stored or cryopreserved plants. Epigenetic stability was evaluated using Methylation Sensitive Amplified Polymorphism (MSAP). Over 36% of the loci were polymorphic when the cold and cryo-treated plants were compared to greenhouse plants. The main changes were demethylation events and they were common to the cryopreserved and cold stored plants indicating the possible effect of the in vitro establishment process, an essential step in both protocols. Protocol-specific methylation patterns were also detected indicating that both methods produced epigenetic changes in plants following cold storage and cryopreservation.

Epigenetic changes detected in micropropagated hop plants

Micropropagation is a widely used technique in hops (Humulus lupulus L.). However, to the best of our knowledge, the genetic and epigenetic stability of the microplants has never been tested before. In the present study, two hop accessions were established in vitro and micropropagated for 2 years. The genetic and epigenetic stability of the in vitro plants was analyzed with several molecular techniques: random amplified DNA polymorphism (RAPD), retrotransposon microsatellite amplified polymorphism (REMAP), and methylation-sensitive amplification polymorphism (MSAP). No genetic variation among control and treated plants was found, even after 12 cycles of micropropagation. Epigenetic variation was detected, first, when field and in vitro samples were compared. Nearly a 30% of the detected fragments presented the same pattern of alterations in all the vitroplants. Second, lower levels of epigenetic variation were detected among plants from the different subcultures. Part of this detected variation seemed to be accumulated along the 12 sequential subcultures tested.

The influence of European and American wild germplasm in hop (Humulus lupulus L.) cultivars

Microsatellite variation at the nuclear and chloroplast genomes was evaluated for wild European and wild American hops, in order to assess the genetic diversity and origin of cultivated hops. Seven nuclear loci and 32 chloroplast loci were used in the analysis of 182 hop accessions including wild European (68), wild American (48), and cultivars (66). A total of 116 alleles were identified using 7 nuclear microsatellites showing different averages of polymorphism and distribution in the wild American and European accessions and cultivars. Two main groups were established as revealed by several statistical analyses; one including European wild accessions and cultivars and a second group consisting of American wild accessions. Three polymorphic chloroplast microsatellite loci were detected, six alleles were scored which defined a total of five haplotypes that were exclusive or presented different distribution between American and European wild accessions. A major influence of the wild European haplotypes was detected among hop cultivars. To the best of our knowledge, this is the first work reporting the use of chloroplast microsatellites in hops.

Evaluation of Microsatellite Detection Using Autoradiography and Capillary Electrophoresis in Hops

Two sequence tagged sites (STS) detection techniques were used in the identification of 25 hop cultivars. In cultivar identification, capillary electrophoresis is more efficient than autoradiography. First, it was more sensitive in detection of fragments that allowed observation of the instability in the locus 7a82 due to the small size differences of its alleles. Additionally, the fluorescent detection of fragments was a nonsubjective technique suitable of automation that increased the flexibility of work because no radioactive labeling or long vertical polyacrylamide electrophoresis was needed. Only two cultivars, Hersbrucker and Hallertauer, were indistinguishable, but further molecular analysis revealed that both were included in a separate cluster within the European hop cultivars. The statistical analysis of fluorescence and radioactive detection data including allelic frequencies, heterozygosity, and probability of identity are displayed in this study, which corroborates the following advantages of the capillary electrophoresis technique: high sensitivity, amenable to automation, and its nonsubjectivity. Therefore, fluorescent-labeled primer microsatellite detection by capillary electrophoresis is a powerful tool in cultivar identification for hop breeders, merchants, and brewers.

Genetic stability of in vitro conserved germplasm of Humulus lupulus L.

The genetic and epigenetic stability of hop accessions cryopreserved for one year or cold stored for three years was evaluated using several molecular markers (RAPD, AFLP, and MSAP). Clear, repetitive patterns were obtained among accessions and between control and treated samples. Although no genetic changes were detected among the control plants grown in the greenhouse and in vitro plants regenerated from slow-cooling cryopreserved shoot tips or cold stored in vitro shoots, MSAP analysis detected methylation changes in 36% of the loci. Nevertheless, only 2.6 to 9.8% of the detected changes could be ascribed to the conservation procedure and most of them seemed to be generated as a result of the in vitro introduction. Due to the number of accessions analysed (51) we can cautiously deduce that the genetic behaviour described in this work after cryopreservation or cold-storage protocols is common to most hop genotypes and these storage procedures are suitable for standard use. However, it is important to keep in mind the epigenetic changes produced, particularly during any in vitro processes.;

IS THE IN VITRO ESTABLISHMENT A CRITICAL POINT IN THE EPIGENETIC STABILITY OF THE CRYOPRESERVED HOPS (HUMULUS LUPULUS L.)

In vitro establishment and micropropagation are basic techniques used as initial step in many of the plant tissue protocols such as cryopreservation. Severe physiological alterations such as changes in leaf structure, water relations and photosynthesis systems are usually associated with the in vitro establishment. In this report, the epigenetic alterations in hops caused by in vitro establishment and micropropagation are assessed using MSAP (methylation-sensitive amplified polymorphism). A 56.3% of the detected loci were monomorphic when the in vitro plants were compared to their donor field plant. Nearly 28.7% of the total loci presented the same alterations of the band profile in all analyzed in vitro plants when compared to the field donor plant. However, when the comparison was performed only among in the micropropagated plants 80.7% of the loci were monomorphic.