Arginine biosynthesis and utilization in maritime pine

Vegetative propagation through somatic embryogenesis in combination with the cryopreservation of embryogenic lines is a major tool in conifer biotechnology. An important process during the maturation phase of embryogenesis is the biosynthesis and deposition of storage proteins. The accumulation of some abundant storage proteins in maturing cotyledonary somatic embryos (SE) is much lower than in mature zygotic embryos (ZE) showing an important influence of storage compounds on the quality of SE. Arginine constitutes a large portion of the amino acid pool in storage proteins of conifers and therefore arginine biosynthesis and utiization is a relevant metabolic pathway during pine embryogenesis and early growth. Research in our laboratory is focused on maritime pine (Pinus pinaster Ait.), a broadly planted conifer species in France, Spain and Portugal where it is distributed over approximately 4 million hectares. This conifer species is also one of the most advanced model trees for genetic and phenotypic studies and a large number of molecular and transcriptomic resources are currently available. With the aim to understand the molecular basis of the differential accumulation of storage proteins in SE and ZE, the arginine metabolic pathway has been studied in maritime pine, in collaboration with the French private institute FCBA. A general overview of this research programme will be presented and discussed. The knowledge acquired from our studies will help to refine biotechnological procedures for clonal propagation of conifers via somatic embryogenesis. Funding support by:The Spanish Ministerio de Economía y Competitividad (BIO2015-69285-R) and Junta de Andalucía (BIO-474). And the French Ministry of Agriculture (DGAL, N°2014-352, QuaSeGraine project). The project also benefited from the technical support of the XYLOBIOTECH facility (ANR-10-EQPX-16 XYLOFOREST).Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

The 5S rDNA family evolves through concerted and birth-and-death evolution in fish genomes: an example from freshwater stingrays

Background: Ribosomal 5S genes are well known for the critical role they play in ribosome folding and functionality. These genes are thought to evolve in a concerted fashion, with high rates of homogenization of gene copies. However, the majority of previous analyses regarding the evolutionary process of rDNA repeats were conducted in invertebrates and plants. Studies have also been conducted on vertebrates, but these analyses were usually restricted to the 18S, 5.8S and 28S rRNA genes. The recent identification of divergent 5S rRNA gene paralogs in the genomes of elasmobranches and teleost fishes indicate that the eukaryotic 5S rRNA gene family has a more complex genomic organization than previously thought. The availability of new sequence data from lower vertebrates such as teleosts and elasmobranches enables an enhanced evolutionary characterization of 5S rDNA among vertebrates.Results: We identified two variant classes of 5S rDNA sequences in the genomes of Potamotrygonidae stingrays, similar to the genomes of other vertebrates. One class of 5S rRNA genes was shared only by elasmobranches. A broad comparative survey among 100 vertebrate species suggests that the 5S rRNA gene variants in fishes originated from rounds of genome duplication. These variants were then maintained or eliminated by birth-and-death mechanisms, under intense purifying selection. Clustered multiple copies of 5S rDNA variants could have arisen due to unequal crossing over mechanisms. Simultaneously, the distinct genome clusters were independently homogenized, resulting in the maintenance of clusters of highly similar repeats through concerted evolution.Conclusions: We believe that 5S rDNA molecular evolution in fish genomes is driven by a mixed mechanism that integrates birth-and-death and concerted evolution

Data from: Dancing together and separate again: gymnosperms exhibit frequent changes of fundamental 5S and 35S rRNA genes (rDNA) organisation

In higher eukaryotes, the 5S rRNA genes occur in tandem units and are arranged either separately (S-type arrangement) or linked to other repeated genes, in most cases to rDNA locus encoding 18S–5.8S–26S genes (L-type arrangement). Here we used Southern blot hybridisation, PCR and sequencing approaches to analyse genomic organisation of rRNA genes in all large gymnosperm groups, including Coniferales, Ginkgoales, Gnetales and Cycadales. The data are provided for 27 species (21 genera). The 5S units linked to the 35S rDNA units occur in some but not all Gnetales, Coniferales and in Ginkgo (~30% of the species analysed), while the remaining exhibit separate organisation. The linked 5S rRNA genes may occur as single-copy insertions or as short tandems embedded in the 26S–18S rDNA intergenic spacer (IGS). The 5S transcript may be encoded by the same (Ginkgo, Ephedra) or opposite (Podocarpus) DNA strand as the 18S–5.8S–26S genes. In addition, pseudogenised 5S copies were also found in some IGS types. Both L- and S-type units have been largely homogenised across the genomes. Phylogenetic relationships based on the comparison of 5S coding sequences suggest that the 5S genes independently inserted IGS at least three times in the course of gymnosperm evolution. Frequent transpositions and rearrangements of basic units indicate relatively relaxed selection pressures imposed on genomic organisation of 5S genes in plants