Oaks are an important part of our natural and cultural heritage. Not only are they ubiquitous in our most common landscapes but they have also supplied human societies with invaluable services, including food and shelter, since prehistoric times. With 450 species spread throughout Asia, Europe and America, oaks constitute a critical global renewable resource. The longevity of oaks (several hundred years) probably underlies their emblematic cultural and historical importance. Such long-lived sessile organisms must persist in the face of a wide range of abiotic and biotic threats over their lifespans. We investigated the genomic features associated with such a long lifespan by sequencing, assembling and annotating the oak genome. We then used the growing number of whole-genome sequences for plants (including tree and herbaceous species) to investigate the parallel evolution of genomic characteristics potentially underpinning tree longevity. A further consequence of the long lifespan of trees is their accumulation of somatic mutations during mitotic divisions of stem cells present in the shoot apical meristems. Empirical and modelling approaches have shown that intra-organismal genetic heterogeneity can be selected for and provides direct fitness benefits in the arms race with short-lived pests and pathogens through a patchwork of intra-organismal phenotypes. However, there is no clear proof that large-statured trees consist of a genetic mosaic of clonally distinct cell lineages within and between branches. Through this case study of oak, we demonstrate the accumulation and transmission of somatic mutations and the expansion of disease-resistance gene families in trees.
We used the combination of preparative electrophoresis and immunological detection to isolate two new proteins from the shell calcitic prisms of Pinna nobilis, the Mediterranean fan mussel. The amino acid composition of these proteins was determined. Both proteins are soluble, intracrystalline, and acidic. The 38-kDa protein is glycosylated; the 17-kDa one is not. Ala, Asx, Thr, and Pro represent the dominant residues of the 38-kDa protein, named calprismin. An N-terminal sequence was obtained from calprismin. This sequence, which comprises a pattern of 4 cysteine residues, is not related to any known protein. The second protein, named caspartin, exhibits an unusual amino acid composition, since Asx constitutes by far the main amino acid residue. Preliminary sequencing surprisingly suggests that the first 75 N-terminal residues are all Asp. Caspartin self-aggregates spontaneously into multimers. In vitro tests show that it inhibits the precipitation of calcium carbonate. Furthermore, it strongly interferes with the growth of calcite crystals. A polyclonal antiserum raised against caspartin was used to localize this protein in the shell by immunogold. The immunolocalization demonstrates that caspartin is distributed within the prisms and makes a continuous film at the interface between the prisms and the surrounding insoluble sheets. Our finding emphasizes the prominent role of aspartic acid-rich proteins for the building of calcitic prisms among molluscs.The secretion of a shell by molluscs is a striking example of a selfassembling process performed outside living tissues. When a mollusc builds its shell, the calcifying epithelium of its mantle extrudes mineral ions, mainly calcium and bicarbonate. In addition, it secretes an extracellular matrix composed of proteins, glycoproteins, proteoglycans, and polysaccharides (1). This mixture is released into the extrapallial space, a microvolume delimited by the epithelium, the growing shell, and the leathery periostracum (2). In this supersaturated space, the released macromolecules interact with bicarbonate and calcium to form biocrystallites that self-aggregate in an orderly manner. The end product is a densely packed organomineral assembly, the shell, in which the mineral phase represents more than 95% by weight (3). As shell proteins exert a control on the biomineralization process, they can be used in the synthesis of biomimetic materials (4 -6). However, the resolution of the primary structure of molluscan shell proteins has been seriously impaired for decades by their polydispersity, their polyanionic properties, and finally their post-translational modifications (3, 7).Despite these obstacles, investigations on molluscan shell proteins have made significant advances in the last 6 years, with the characterization of 16 proteins and, for most of them, the identification of the corresponding transcript (8, 9). Among the different shell textures that molluscs use to produce their shell, mother-of-pearl has received the greatest deal of attention. Its intrinsic bea...
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