Viral nano-hybrids for innovative energy conversion and storage schemes.

Typical rod-like viruses (the Tobacco Mosaic Virus (TMV) and the Bacteriophage M13) are biological nanostructures that couple a 1D mono-dispersed morphology with a precisely defined topology of surface spaced and orthogonal reactive domains. These biogenic scaffolds offer a unique alternative to synthetic nano-platforms for the assembly of functional molecules and materials. Spatially resolved 1D arrays of inorganic-organic hybrid domains can thus be obtained on viral nano-templates resulting in the functional arrangement of photo-triggers and catalytic sites with applications in light energy conversion and storage. Different synthetic strategies are herein highlighted depending on the building blocks and with a particular emphasis on the molecular design of viral-templated nano-interfaces holding great potential for the dream-goal of artificial photosynthesis.

A novel E-type endo-beta-1,4-glucanase with a putative cellulose-binding domain is highly expressed in ripening strawberry fruits.

Two full-length cDNA clones (faEG1 and faEG3, respectively) have been isolated by screening a cDNA library representing transcripts from red strawberry fruits. Southern blot analysis of genomic DNA suggests that the strawberry endo-beta-1,4-glucanases (EGases) are encoded by a multigene family. The cognate genes are predominantly expressed during the ripening process proper, although, in the case of faEG3, some expression has also been observed in large green fruits and, at low amounts, in young vegetative green tissues. In agreement with other ripening-related genes in strawberry, also the expression of faEG1 and faEG3 is down-regulated by treatment with an auxin analogue (1-naphthaleneacetic acid, NAA). Differences in temporal expression of the two EGase genes in fruits are not accompanied by differences in spatial expression. The pattern of expression and the sequence characteristics of the two polypeptides suggest that the two strawberry EGases operate in a synergistic and coordinate manner. The protein encoded by faEG1 looks like one of the usual higher-plant EGases (average molecular mass of 54 kDa), while the protein encoded by faEG3 has a greater deduced molecular mass (about 68 kDa) due to the presence of an extra peptide of about 130 amino acids at the C-terminus. Such unusual peptide shows some features also found in microbial cellulases and contains a putative cellulose-binding domain. We propose that the faEG3-encoded EGase might especially hydrolyse the xyloglucans coating the cellulose microfibrils, thus rendering the cell wall more susceptible to the subsequent hydrolytic activity of the faEG1-encoded EGase.

Characterization of ppEG1, a member of a multigene family which encodes endo-beta-1,4-glucanase in peach.

Three cDNA clones (pCel 10, pCel 20 and pCel 30), each encoding different endo-beta-1,4-glucanases in peach, were obtained by RT-PCR and their expression investigated by northern analysis during leaf and fruit abscission and during fruit development. This analysis allowed the detection of only the pCel 10-related mRNA. A 2.2 kb transcript accumulated in ethylene activated abscission zones of leaves and fruits, and ppEG1 (Prunus persica endoglucanase 1) the gene coding for pCel 10, was isolated and characterized. A cDNA (termed pCel 1), containing the entire open reading frame of ppEGC1, was obtained and its sequence used to define the structure of the gene and the exon/intron boundaries. ppEG1 consists of 7 exons and encodes a 497 amino acid polypeptide including a putative signal peptide at the N-terminus. The similarity of this peach endo-beta-1,4-glucanase (EGase, EC 3.2.1.4) is high (76.3%) with the ripening avocado and low (47.3%) with the bean abscission EGase. A 1639 bp region at the 5' of the transcription start site shows regulatory functions in transgenic tobacco plants, as judged by its ability to drive GUS expression in cell separation-related events.

Differential ethylene-inducible expression of cellulase in pepper plants.

Ethylene promotes the abscission of leaves and the ripening of fruits in pepper plants, and in both events an increase in cellulase activity is observed. However, two enzyme isoforms (pI 7.2 and 8.5, respectively) are differentially involved in the two physiological phenomena. The pI 8.5 form has been purified from ripe fruits. It is a glycoprotein with an apparent molecular mass of 54 kDa. Two short peptides were sequenced and a very high homology to a tomato cellulase was observed. Polyclonal antibodies, raised against the purified enzyme, have allowed us to demonstrate that the observed ethylene-induced increase in cellulase activity is paralleled by de novo synthesis of protein. Three cDNAs (CX1, CX2 and CX3), encoding different cellulases, were obtained and characterized and their expression investigated. Accumulation of all three mRNAs is induced by ethylene treatment, though to different levels. CX1 is mainly expressed in ripe fruits while CX2 is especially found in abscission zones. CX3 accumulates at very low levels in activated abscission zones. Comparisons with other known cellulases demonstrate clear heterogeneity within the higher plant cellulases. Differences in ethylene inducibility and molecular structure suggest different physiological roles for cellulase in pepper plants.

Isolation, sequencing and expression of cDNA sequences encoding uroporphyrinogen decarboxylase from tobacco and barley.

We have cloned and sequenced a full-length cDNA for uroporphyrinogen decarboxylase (UROD, EC 4.1.1.37) from tobacco (Nicotiana tabacum L.) and a partial cDNA clone from barley (Hordeum vulgare L.). The cDNA of tobacco encodes a protein of 43 kDa, which has 33% overall similarity to UROD sequences determined from other organisms. We propose that tobacco UROD has an N-terminal extension of 39 amino acid residues. This extension is most likely a chloroplast transit sequence. The in vitro translation product of UROD was imported into pea chloroplasts and processed to ca. 39 kDa. A truncated cDNA, from which the putative transit peptide had been deleted, was used to over-express the mature UROD in Escherichia coli. Purified protein showed UROD activity, thus providing an adequate source for subsequent enzymatic characterization and inhibition studies. Expression of UROD was investigated by northern and western blot analysis during greening of etiolated barley seedlings, and in segments of barley primary leaves grown under day/night cycles. The amount of RNA and protein increased during illumination. Maximum UROD-RNA levels were detected in the basal segments relative to the top of the leaf.