Isolation and sequencing of a cDNA clone encoding a 20-kDa protein with trypsin inhibitory activity

An Alternative Nested Reading Frame May Participate in the Stress-Dependent Expression of a Plant Gene

Although plants as sessile organisms are affected by a variety of stressors in the field, the stress factors for the above-ground and underground parts of the plant and their gene expression profiles are not the same. Here, we investigated NbKPILP, a gene encoding a new member of the ubiquitous, pathogenesis-related Kunitz peptidase inhibitor (KPI)-like protein family, that we discovered in the genome of Nicotiana benthamiana and other representatives of the Solanaceae family. The NbKPILP gene encodes a protein that has all the structural elements characteristic of KPI but in contrast to the proven A. thaliana KPI (AtKPI), it does not inhibit serine peptidases. Unlike roots, NbKPILP mRNA and its corresponding protein were not detected in intact leaves, but abiotic and biotic stressors drastically affected NbKPILP mRNA accumulation. In search of the causes of suppressed NbKPILP mRNA accumulation in leaves, we found that the NbKPILP gene is "matryoshka," containing an alternative nested reading frame (ANRF) encoding a 53-amino acid (aa) polypeptide (53aa-ANRF) which has an amphipathic helix (AH). We confirmed ANRF expression experimentally. A vector containing a GFP-encoding sequence was inserted into the NbKPILP gene in frame with 53aa-ANRF, resulting in a 53aa-GFP fused protein that localized in the membrane fraction of cells. Using the 5'-RACE approach, we have shown that the expression of ANRF was not explained by the existence of a cryptic promoter within the NbKPILP gene but was controlled by the maternal NbKPILP mRNA. We found that insertion of mutations destroying the 53aa-ANRF AH resulted in more than a two-fold increase of the NbKPILP mRNA level. The NbKPILP gene represents the first example of ANRF functioning as a repressor of a maternal gene in an intact plant. We proposed a model where the stress influencing the translation initiation promotes the accumulation of NbKPILP and its mRNA in leaves.

Purification of a Kunitz-type inhibitor from Acacia polyphyllaDC seeds: characterization and insecticidal properties against Anagasta kuehniella Zeller (Lepidoptera: Pyralidae)

Anagasta kuehniella is a polyphagous pest that causes economic losses worldwide. This species produces serine proteases as its major enzymes for protein digestion. In this study, a new serine-protease inhibitor was isolated from Acacia polyphylla seeds (AcKI).Further analysis revealed that AcKI is formed by two polypeptide chains with a relative molecular mass of ∼20 kDa. The effects of AcKI on the development, survival, and enzymatic activity of Anagasta kuehniella larvae were evaluated, by incorporating AcKI in an artificial diet. Bioassays revealed a reduction in larval weight of ∼50% with the lower concentration of AcKI used in the study (0.5%). Although additionalassays showed an increase in endogenous trypsin and chymotrypsin activities, with a degree of AcKI-insensivity, AcKI produces an anti nutritional effect on A. kuehniella, indicating AcKI as a promising bioinsecticide protein for engineering plants that are resistant to insect pests.

Cloning, characterization and expression analysis of a novel gene encoding Kunitz-type protease inhibitor from Dolichos biflorus

This paper reports the presence of a Kunitz-type protease inhibitor (HGPI) gene in Dolichos biflorus for the first time. A full-length protease inhibitor gene with complete open reading frame of 669 bp encoding 222 amino acids was cloned from D. biflorus using a PCR-based method. BlastN search showed that the HGPI gene shared 100% homology with Cicer arietinum trypsin inhibitor mRNA and 97% with Cajanus cajan protease inhibitor. The deduced amino acid sequence exhibited homology with Kunitz-type trypsin inhibitor from chickpea, pigeon pea and soybean. The deduced amino acid sequence contained N-terminal signal sequence of 18 amino acids and had a molecular weight of 24 kDa. The phylogenetic tree also showed close relationship with Cicer arietinum and Cajanus cajan. Southern blotting revealed the presence of only one copy of HGPI gene in the D. biflorus genome. Homology modeling was employed to predict secondary structure and 3D-structural models for the protease inhibitor. The gene was found to be constitutively expressed in different tissues as determined by semi-quantitative RT-PCR. The novel HGPI gene has been submitted to the GenBank with Accession No. FN666416. The isolated novel HGPI gene will broaden the pool of plant defense genes and might be an ideal choice for developing transgenic crops resistant to insect pests, as well as pathogens. In addition, it could be used as a probe for selection of insect- and pathogen-resistant genotypes.

Geraniol-inducible glutathione S-transferase in cultured soybean cells

When the cultured cells of Glycine max (soybean) were treated with 5 mM geraniol as a chemical stress, an mRNA level was elevated in a rapid but transient increase. The mRNA was cloned and sequenced, and found to correspond to the mRNA encoding glutathione S-transferase (GST). The GST mRNA level and GST activity were elevated to maxima at 4-6 h and 8 h, respectively, after treatment of the cultures with geraniol. These indicate that GST is one of the geraniol-responsive factors in soybean cells.