Changes during development of red- and white-fleshed apple cultivar

Europäische Kommissio

The Mechanism of Resistance of EUROPEAN Plum to Plum pox virus Mediated by Hypersensitive Response Is Linked to VIRAL NIa and Its Protease Activity

Plum pox virus (PPV) infects Prunus trees across the globe, causing the serious Sharka disease. Breeding programs in the past 20 years have been successful, generating plum varieties hypersensitive to PPV that show resistance in the field. Recently, a single tree displaying typical PPV symptoms was detected in an orchard of resistant plums. The tree was eradicated, and infected material was propagated under controlled conditions to study the new PPV isolate. Performing overlapping PCR analysis, the viral sequence was reconstructed, cloned and tested for infectivity in different ‘Jojo’-based resistant plums. The results confirmed that the isolate, named PPV-D ‘Herrenberg’ (PPVD-H), was able to infect all these varieties. Analyses of chimeras between PPVD-H and a PPV-D standard isolate (PPVD) revealed that the NIa region of PPD-H, carrying three amino acid changes, was enough to break the resistance of these plums. Experiments with single and double mutants showed that all changes were essential to preserve the escaping phenotype. Additionally, one of the changes at the VPg-NIapro junction suggested the involvement of controlled endopeptidase cleavage in the viral response. Transient expression experiments in Nicotiana benthamiana confirmed that NIa cleavage in PPVD-H was reduced, compared to PPVD, linking the observed behavior to an NIa cleavage modulation

Chemoecology / Flowers of European pear release common and uncommon volatiles that can be detected by honey bee pollinators

Floral scents are important pollinator attractants, but there is limited knowledge about the importance of single components in plantpollinator interactions. This especially is true in crop pollination systems. The aim of this study is to identify floral volatiles of several European pear cultivars (Pyrus communis L.), and to determine their potential in eliciting physiological responses in antennae of honey bees (Apis mellifera L.), the most important pollinators of pear. Volatiles were collected by dynamic headspace and analysed by (high resolution) gas chromatography coupled to mass spectrometry (GC/MS) and nuclear magnetic resonance spectroscopy. Antennal responses were investigated by GC coupled to electroantennographic detection (GC/EAD). We trapped in the mean 256 ng of scent per flower and hour (flower1 h1) from the different cultivars with either linalool + methyl benzoate or methyl 2-hydroxy-3-methylpentanoate as most abundant compounds. Of the 108 detected pear floral scent components, 17 were electrophysiologically active in honey bee antennae. Among these compounds were (E)-N-(2-methylbutyl)- and (E)-N-(3-methylbutyl)-1-(pyridin-3-yl)methanimine, which were not known from nature before to the best of our knowledge. Most other compounds identified as flower scent in pear are widespread compounds, known from flowers of various other species. Our results provide new insights in the floral volatile chemistry of an important insect-pollinated crop and show for the first time that honey bees have the olfactory ability to detect several pear floral volatiles. These data are an important basis for more detailed studies of the olfactory communication between honey bees and European pear flowers and might in the long term be used to manipulate the attractiveness of pear to obtain optimal fruit set.(VLID)459312

Phenolic profiling of red-fleshed apples

Europäische Kommissio

Changes in the flavonoid pathway during the last four weeks of fruit ripening in an apple cultivar showing bicolored fruit flesh

Europäische Kommissio

Metabolite investigations of poinsettia cultivars

Europäische Kommissio

The rare orange-red colored Euphorbia pulcherrima cultivar ‘Harvest Orange’ shows a nonsense mutation in a flavonoid 3’-hydroxylase allele expressed in the bracts

Abstract Background Commercially available poinsettia (Euphorbia pulcherrima) varieties prevalently accumulate cyanidin derivatives and show intense red coloration. Orange-red bract color is less common. We investigated four cultivars displaying four different red hues with respect to selected enzymes and genes of the anthocyanin pathway, putatively determining the color hue. Results Red hues correlated with anthocyanin composition and concentration and showed common dark red coloration in cultivars ‘Christmas Beauty’ and ‘Christmas Feeling’ where cyanidin derivatives were prevalent. In contrast, orange-red bract color is based on the prevalent presence of pelargonidin derivatives that comprised 85% of the total anthocyanin content in cv. ‘Premium Red’ and 96% in cv. ‘Harvest Orange’ (synonym: ‘Orange Spice’). cDNA clones of flavonoid 3′-hydroxylase (F3′H) and dihydroflavonol 4-reductase (DFR) were isolated from the four varieties, and functional activity and substrate specificity of the corresponding recombinant enzymes were studied. Kinetic studies demonstrated that poinsettia DFRs prefer dihydromyricetin and dihydroquercetin over dihydrokaempferol, and thus, favor the formation of cyanidin over pelargonidin. Whereas the F3′H cDNA clones of cultivars ‘Christmas Beauty’, ‘Christmas Feeling’, and ‘Premium Red’ encoded functionally active enzymes, the F3′H cDNA clone of cv. ‘Harvest Orange’ contained an insertion of 28 bases, which is partly a duplication of 20 bases found close to the insertion site. This causes a frameshift mutation with a premature stop codon after nucleotide 132 and, therefore, a non-functional enzyme. Heterozygosity of the F3′H was demonstrated in this cultivar, but only the mutated allele was expressed in the bracts. No correlation between F3′H-expression and the color hue could be observed in the four species. Conclusions Rare orange-red poinsettia hues caused by pelargonidin based anthocyanins can be achieved by different mechanisms. F3′H is a critical step in the establishment of orange red poinsettia color. Although poinsettia DFR shows a low substrate specificity for dihydrokaempferol, sufficient precursor for pelargonidin formation is available in planta, in the absence of F3’H activity

The rare orange-red colored Euphorbia pulcherrima cultivar 'Harvest Orange' shows a nonsense mutation in a flavonoid 3'-hydroxylase allele expressed in the bracts

Background: Commercially available poinsettia (Euphorbia pulcherrima) varieties prevalently accumulate cyanidin derivatives and show intense red coloration. Orange-red bract color is less common. We investigated four cultivars displaying four different red hues with respect to selected enzymes and genes of the anthocyanin pathway, putatively determining the color hue. Results: Red hues correlated with anthocyanin composition and concentration and showed common dark red coloration in cultivars 'Christmas Beauty' and 'Christmas Feeling' where cyanidin derivatives were prevalent. In contrast, orange-red bract color is based on the prevalent presence of pelargonidin derivatives that comprised 85% of the total anthocyanin content in cv. 'Premium Red' and 96% in cv. 'Harvest Orange' (synonym: 'Orange Spice'). cDNA clones of flavonoid 3'-hydroxylase (F3'H) and dihydroflavonol 4-reductase (DFR) were isolated from the four varieties, and functional activity and substrate specificity of the corresponding recombinant enzymes were studied. Kinetic studies demonstrated that poinsettia DFRs prefer dihydromyricetin and dihydroquercetin over dihydrokaempferol, and thus, favor the formation of cyanidin over pelargonidin. Whereas the F3'H cDNA clones of cultivars 'Christmas Beauty', 'Christmas Feeling', and 'Premium Red' encoded functionally active enzymes, the F3'H cDNA clone of cv. 'Harvest Orange' contained an insertion of 28 bases, which is partly a duplication of 20 bases found close to the insertion site. This causes a frameshift mutation with a premature stop codon after nucleotide 132 and, therefore, a non-functional enzyme. Heterozygosity of the F3'H was demonstrated in this cultivar, but only the mutated allele was expressed in the bracts. No correlation between F3'H-expression and the color hue could be observed in the four species. Conclusions: Rare orange-red poinsettia hues caused by pelargonidin based anthocyanins can be achieved by different mechanisms. F3'H is a critical step in the establishment of orange red poinsettia color. Although poinsettia DFR shows a low substrate specificity for dihydrokaempferol, sufficient precursor for pelargonidin formation is available in planta, in the absence of F3'H activity