Genetische Kartierung des Inflorenszenztyps mittels Genotyping-by-Sequencing bei Hortensie (Hydrangea macrophylla)

Hortensien (Hydrangea macrophylla) lassen sich durch die Anordnung und Anzahl ihrer Schaublüten in sogenannte Teller- und Ballhortensien unterscheiden. Bei Tellerhortensien besteht der Blütenstand vorwiegend aus vielen kleinen, fertilen Blüten. Diese sind von wenigen großen, sterilen Schaublüten umrandet. Dagegen weist der Blütenstand von Ballhortensien deutlich mehr Schaublüten auf. Diese sind über den gesamten Blütenstand verteilt, wodurch der ballförmige Infloreszenztyp entsteht. Die Ballform ist wegen ihres größeren Verkaufswertes züchterisch bevorzugt. Die Ballform wird monogen, rezessiv vererbt, die Tellerform dominant (Meier, 1990; Uemachi und Okumura, 2012). Kreuzt man eine Ball- mit einer Tellerhortensie, dann prägen alle Nachkommen die Tellerform aus. Erst durch Rückkreuzung mit einer weiteren Ballhortensie spaltet die nachfolgende Generation in Ball- und Tellerform auf, so dass Ballhortensien selektiert werden können. Hortensien blühen frühestens 13 Monate nach der Aussaat. Erst dann ist eine Bestimmung des Infloreszenztyps möglich. Mittels markergestützter Selektion können Allele, die die Ballform kodieren, leichter in komplexen Erbgängen nachverfolgt und Sämlinge bereits im Keimlingsstadium als Ballhortensien identifiziert werden. Um Gene zu identifizieren, die die Ausprägung des Infloreszenztyps kontrollieren, wurde eine Ball- mit einer F1-Tellerhortensie gekreuzt, um eine Pseudo-Rückkreuzungspopulation (pBC1) zu erzeugen. Diese Population umfasst 424 Individuen und spaltet für Teller- und Ballform im Verhältnis 3:1 (Χ2 = 0,034, nicht-signifikant bei α = 0,05) auf. Bei monogener Vererbung wäre jedoch ein Spaltungsverhältnis von 1:1 zu erwarten. Eine 3:1-Spaltung tritt dagegen bei einer digenen, dominant-rezessiven Vererbung auf. Deshalb nehmen wir an, dass die Ausprägung des Infloreszenztyps in unserer Population durch zwei Gene erfolgt. Für die Kartierung dieser Gene wird eine QTL-Analyse durchgeführt. Zur Erstellung der genetischen Karte wurde an 381 ausgewählten pBC1-Pflanzen eine genomweite Markeranalyse mittels Genotyping-by-Sequencing durchgeführt. Erste Sequenzier- und Kartierungsergebnisse werden präsentiert

A Detailed Analysis of the BR1 Locus Suggests a New Mechanism for Bolting after Winter in Sugar Beet (Beta vulgaris L.)

Sugar beet (Beta vulgaris ssp. vulgaris) is a biennial, sucrose-storing plant, which is mainly cultivated as a spring crop and harvested in the vegetative stage before winter. For increasing beet yield, over-winter cultivation would be advantageous. However, bolting is induced after winter and drastically reduces yield. Thus, post-winter bolting control is essential for winter beet cultivation. To identify genetic factors controlling bolting after winter, a F2 population was previously developed by crossing the sugar beet accessions BETA 1773 with reduced bolting tendency and 93161P with complete bolting after winter. For a mapping-by-sequencing analysis, pools of 26 bolting-resistant and 297 bolting F2 plants were used. Thereby, a single continuous homozygous region of 103 kb was co-localized to the previously published BR1 QTL for post-winter bolting resistance (Pfeiffer et al., 2014). The BR1 locus was narrowed down to 11 candidate genes from which a homolog of the Arabidopsis CLEAVAGE AND POLYADENYLATION SPECIFICITY FACTOR 73-I (CPSF73-I) was identified as the most promising candidate. A 2 bp deletion within the BETA 1773 allele of BvCPSF73-Ia results in a truncated protein. However, the null allele of BvCPSF73-Ia might partially be compensated by a second BvCPSF73-Ib gene. This gene is located 954 bp upstream of BvCPSF73-Ia and could be responsible for the incomplete penetrance of the post-winter bolting resistance allele of BETA 1773. This result is an important milestone for breeding winter beets with complete bolting resistance after winter

RNA-Mediated Gene Silencing Signals Are Not Graft Transmissible from the Rootstock to the Scion in Greenhouse-Grown Apple Plants Malus sp.

RNA silencing describes the sequence specific degradation of RNA targets. Silencing is a non-cell autonomous event that is graft transmissible in different plant species. The present study is the first report on systemic acquired dsRNA-mediated gene silencing of transgenic and endogenous gene sequences in a woody plant like apple. Transgenic apple plants overexpressing a hairpin gene construct of the gusA reporter gene were produced. These plants were used as rootstocks and grafted with scions of the gusA overexpressing transgenic apple clone T355. After grafting, we observed a reduction of the gusA gene expression in T355 scions in vitro, but not in T355 scions grown in the greenhouse. Similar results were obtained after silencing of the endogenous Mdans gene in apple that is responsible for anthocyanin biosynthesis. Subsequently, we performed grafting experiments with Mdans silenced rootstocks and red leaf scions of TNR31-35 in order to evaluate graft transmitted silencing of the endogenous Mdans. The results obtained suggested a graft transmission of silencing signals in in vitro shoots. In contrast, no graft transmission of dsRNA-mediated gene silencing signals was detectable in greenhouse-grown plants and in plants grown in an insect protection tent

Molecular Reconstruction of an Old Pedigree of Diploid and Triploid Hydrangea macrophylla Genotypes

The ornamental crop species Hydrangea macrophylla exhibits diploid and triploid levels of ploidy and develops lacecap (wild type) or mophead inflorescences. In order to characterize a H. macrophylla germplasm collection, we determined the inflorescence type and the 2C DNA content of 120 plants representing 43 cultivars. We identified 78 putative diploid and 39 putative triploid plants by flow cytometry. In our collection 69 out of 98 flowering plants produced lacecap inflorescences, whereas 29 plants developed mophead inflorescences. Surprisingly, 12 cultivars included diploid as well as triploid plants, while 5 cultivars contained plants with different inflorescence types. We genotyped this germplasm collection using 12 SSR markers that detected 2–7 alleles per marker, and identified 51 different alleles in this collection. We detected 62 distinct fingerprints, revealing a higher genetic variation than the number of cultivars suggested. Only one genotype per cultivar is expected due to the vegetative propagation of Hydrangea cultivars; however we identified 25 cultivars containing 2–4 different genotypes. These different genotypes explained the variation in DNA content and inflorescence type. Diploid and triploid plants with the same cultivar name were exclusively mix-ups. We therefor assume, that 36% of the tested plants were mislabeled. Based on the “Wädenswil” pedigree, which includes 31 of the tested cultivars, we predicted cultivar-specific fingerprints and identified at least 21 out of 31 cultivars by SSR marker-based reconstruction of the “Wädenswil” pedigree. Furthermore, we detected 4 putative interploid crosses between diploid and triploid plants in this pedigree. These interploid crosses resulted in diploid or/and triploid offspring, suggesting that crosses with triploids were successfully applied in breeding of H. macrophylla

Deciphering the complex nature of bolting time regulation in Beta vulgaris

International audienc