Search

Oaks taxonomy has been revised over the years, demanding expeditious and cost-effective tools for DNA fingerprinting and taxonomic discrimination. We focused on the characterization of the ribosomal DNA (rDNA) of 22 Quercus species, belonging to four infrageneric groups, using silver nitrate staining, fluorescence in situ hybridization (FISH) and IGS PCR-RFLP markers (produced by the digestion of the rDNA intergenic spacer, IGS). A chromosome complement of 2 n = 2 x = 24 was confirmed in 21 species, and ascribed to Quercus phellos. Silver nitrate staining detected one or two nucleoli per nucleus, and two nucleolar organizer regions (NORs) per prometaphase cells. FISH performed with rDNA probes revealed two 5S and four 35S rDNA loci in nine species and confirmed their location in the remaining. Since no cytogenetic polymorphisms were detected, the IGS was studied. A single amplicon with ca. 2 kb was amplified in all oaks, and digested with six restriction enzymes, that produced a total of 125 IGS PCR-RFLP fragments with 99.2 % of polymorphism. A monomorphic HaeIII fragment with 225 bp was found. Among the infrageneric groups, 11 monomorphic bands were observed and 6 were considered group-specific. Based on the pool of molecular data different genetic analyses were performed. The UPGMA dendrogram clustered most of the oaks per infrageneric group, and was corroborated by the principal coordinates analysis (PCoA). The genetic structure also matched the assumed taxonomy. Globally, IGS PCR-RFLP proved their usefulness for DNA fingerprinting, evaluation of phylogenies and genetic structure, proving to be an adequate complementary tool for rDNA based studies in genus Quercus. [ABSTRACT FROM AUTHOR]

The Fagaceae is one of the most important plant families in European forest ecosystems, and it includes several genera distributed in the Northern hemisphere. In this work we studied the genome organization and evolution within the family, by karyotyping and physically mapping rDNA in ten European and Asian species of the genera Fagus, Quercus, and Castanea. All of the species studied had a chromosome number of 2n=2 x=24, except for the first report of a single individual of Quercus suber which proved to be triploid (2n=3 x=36). The rDNA physical mapping revealed several patterns: the dominant one is present in European and Asian Quercus subgenus Quercus, and in Castanea sativa and Castanea crenata, consisting of two 18S-25S rDNA loci (one subterminal major and one pericentromeric minor) and one 5S rDNA pericentromeric locus. In Fagus sylvatica and in Quercus sessilifolia, different patterns were observed: four terminal 18S-25S rDNA loci and two 5S rDNA pericentromeric loci in the former, and five 18S-25S rDNA loci (three terminal and two intercalary) and one 5S rDNA pericentromeric locus in the latter. In Castanea mollissima a distinct rDNA distribution pattern with two intercalary 18S-25S rDNA loci and two 5S rDNA was found. These findings suggest rDNA loci restructuring during Castanea evolution, and variability of 18S-25S loci between Quercus and Cyclobalanopsis subgenera. [ABSTRACT FROM AUTHOR]

We have analysed the distribution of epigenetic marks for histone modifications at lysine residues H3 and H4, and DNA methylation, in the nuclei of mature pollen cells of the Angiosperm tree Quercus suber; a monoecious wind pollinated species with a protandrous system, and a long post-pollination period. The ultrasonic treatment developed for the isolation of pollen nuclei proved to be a fast and reliable method, preventing the interference of cell wall autofluorescence in the in situ immunolabelling assays. In contrast with previous studies on herbaceous species with short progamic phases, our results are consistent with a high level of silent (5-mC and H3K9me2) epigenetic marks on chromatin of the generative nucleus, and the prevalence of active marks (H3K9me3 and H4Kac) in the vegetative nucleus. The findings are discussed in terms of the pollination/fertilization timing strategy adopted by this plant species. [ABSTRACT FROM AUTHOR]

The complete sequence of the first retrotransposon isolated in Vitis vinifera, Gret1, was used to design primers that permitted its analysis in the genome of grapevine cultivars. This retroelement was found to be dispersed throughout the genome with sites of repeated insertions. Fluorescent in situ hybridization indicated multiple Gret1 loci distributed throughout euchromatic portions of chromosomes. REMAP and IRAP proved to be useful as molecular markers in grapevine. Both of these techniques showed polymorphisms between cultivars but not between clones of the same cultivar, indicating differences in Gret1 distribution between cultivars. The combined cytological and molecular results suggest that Gret1 may have a role in gene regulation and in explaining the enormous phenotypic variability that exists between cultivars. [ABSTRACT FROM AUTHOR]

Cork oak (Quercus suber L.) is one of the most important Mediterranean forest tree species. The last decades have been marked by a decline in this species. Implementation of breeding programs is fundamental to revert this trend. Somatic embryogenesis is the system of choice for clonal propagation, constituting a valuable tool for embryo production and improved genotype testing. In this study, the cork oak transcriptome during somatic embryogenesis was characterized in four stages of development to identify relevant genes in the process and to understand the molecular and biochemical events occurring in each specific stage. A total 66,693 candidate coding regions were predicted from the generated de novo transcriptome assembly. Differential gene expression analysis identified 11,507 genes distributed in 30 clusters with distinct gene expression patterns and enriched in various biological process GO terms. Results show 1159 differentially expressed genes coding for transcription regulators, namely transcription factors (76%) with important roles in embryogenesis, like orthologous of AINTEGUMENTA-like, PLETHORA, CYTOKININ RESPONSE FACTOR, GATA transcription factors, and AUXIN RESPONSE FACTORs genes. Results also show 250 differentially expressed phytohormone-related genes involved in important aspects of embryogenesis as tissue specification, differentiation, and embryogenesis competence. Finally, we identified a group of genes with functions in cellular protection and abiotic stress tolerance coding for LATE EMBRYOGENESIS ABUNDANT proteins. Cork oak embryogenesis transcriptome characterization represents a tool for future biotechnological applications. Our results provide a molecular insight into embryo development, establishing a basis for further research towards improvement of somatic embryogenesis in cork oak. [ABSTRACT FROM AUTHOR]