Subcellular localization of the 2S globulin narbonin in seeds of Vicia narbonensis

Abstract

Narbonin is a 2S protein from the globulin fraction of narbon bean (Vicia narbonensis L.) cotyledons. Its amino acid composition and the pattern of its regulated accumulation in developing seeds led to the suggestion that narbonin could be a storage protein. Therefore, it was expected to be present in protein bodies of the storage tissue cells. Comparison of the cDNA-derived amino acid sequence with a directly determined partial N-terminal sequence revealed that the primary translation product of narbonin mRNA lacks a transient N-terminal signal peptide (V.H. Nong et al., 1995, Plant Mol Biol 28: 61 - 72). Narbonin polypeptides that had been synthesized in a cell-free translation system supplemented with dog pancreas microsomes were not protected against degradation by posttranslationally added proteases (protease protection assay). In accordance with the lack of a signal peptide this indicates that the polypeptide was not cotranslationally sequestered into the microsomes. The protein-body fraction that had been isolated from mature narbon bean cotyledons by a non-aqueous gradient centrifugation procedure was free of narbonin; this was found in the soluble cell fraction. In electron micrographs, narbonin could be localized in the cytoplasm using the immuno gold-labelling technique. Previously, it had already been shown that narbonin is too slowly degraded during narbon bean germination to act as a storage protein. From all these results it has to be concluded that narbonin is a cytoplasmic protein which does not belong to the storage proteins in the restricted sense. Other possible functions are discussed.

Global changes in gene expression during compatible and incompatible interactions of cowpea (Vigna unguiculata L.) with the root parasitic angiosperm Striga gesnerioides

“…Among the genes most highly induced were a number of chitinases and chitinase homologs including narbonin, a protein with glycosyl hydrolase activity [26] whose biological function has yet to be elucidated [27]. Narbonin has been previously suggested as interfering with parasite growth in the root by altering cell wall extensibility [19].…”

The BURP domain protein AtUSPL1 of Arabidopsis thaliana is destined to the protein storage vacuoles and overexpression of the cognate gene distorts seed development

“…For VfUSP localisation in developing cotyledons of Vicia faba samples were prepared, sectioned and labelled according to the protocol described in Steffens et al (1997). Polyclonal antibodies raised against recombinant VfUSP protein were used for immunolocalization in combination with gold-labelled goat anti-rabbit IgG (BioCell, Cardiff, UK).…”

Chitinases in root nodules

“…In this analysis, all full size sequences of chitinases studied in roots and/or nodules of legumes and actinorhizal plants were included ( Figure 1). Two nodule-specific chitinase homologues from broad been (NVf32a, b) were found to be expressed in the nitrogen-fixing zone of the inner tissue of the nodule (Perlick et al 1996) but since the encoded proteins do not contain a full glycoside hydrolase (GH) 18 domain and their highest homology is to Narbonins (2S seed storage proteins), for which no enzymatic function could be detected (Steffens et al 1997), NVf32a and b were not included in the phylogenetic analysis.…”