A wound-inducible gene from Salix viminalis coding for a trypsin inhibitor

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.

Two cell wall Kunitz trypsin inhibitors in chickpea during seed germination and seedling growth

Two Kunitz trypsin inhibitors TPI-1 and TPI-2, encoded by CaTPI-1 and CaTPI-2, previously identified and characterized, have been detected in chickpea (Cicer arietinum L.) embryonic axes from seeds imbibed up to 48 h. Their gene transcription commenced before germination sensu stricto was completed. The transcript amount of CaTPI-1 remained high until 24 h after imbibition, when the epicotyls started to grow, while CaTPI-2 mRNA, which appeared later, reached a maximum at 48 h. Both the temporal and the spatial distribution of TPI-1 and TPI-2 proteins in the embryonic axes suggest that they perform different functions. The early appearance of TPI-1 in imbibed seeds suggests that it plays a protective role, preventing the premature degradation of the proteins stored in the embryonic axes. Its pattern of distribution suggests that the protein is involved in the regulation of vascular tissue differentiation, protecting the cells from some proteinases involved in programmed cell death. With regard to TPI-2, its later synthesis after imbibition, together with its tissue distribution, indicates that it is mainly active following germination, during elongation of the embryonic axes.

Trypsin inhibitors in passion fruit (Passiflora f. edulis flavicarpa) leaves: accumulation in response to methyl jasmonate, mechanical wounding, and herbivory

This work investigates the effect of methyl jasmonte (MeJa), mechanical wounding, and herbivory caused by larval feeding of a specialist insect ( Agraulis vanillae vanillae) upon trypsin inhibitory activity in passion fruit leaves. Despite the fact that all treatments caused accumulation of trypsin inhibitors (TIs), higher levels were observed in MeJa treated leaves when plants were assayed 24 and 48 h after stimulus. Concerning both mechanically injured plants and attacked ones, a systemic induction was observed. Partially purified inhibitors from MeJa exposed plants were further characterized by X-ray film contact print technique and N-terminal sequence. Such analysis indicated that the TIs identified belong to the Kunitz family. Moreover, the partially purified inhibitors strongly inhibited trypsin-like digestive enzymes from sugar cane stalk borer ( Diatraea saccharalis) in vitro. Our results further support the protective function of wound-inducible trypsin inhibitors and their potential as tools to improve important crop species against insect predation through genetic engineering.

A chickpea Kunitz trypsin inhibitor is located in cell wall of elongating seedling organs and vascular tissue

Kunitz proteinase inhibitors in legumes have mainly been described as defence and storage proteins. Here, we report a Kunitz trypsin inhibitor, encoded by the CaTPI-1 gene from Cicer arietinum. The transcription of this gene mainly occurs in seedling vegetative organs, and is affected by the light and growth stages. The recombinant TPI-1 protein expressed in E. coli was seen to be an efficient inhibitor of trypsin. After the generation of polyclonal antibodies against recombinant TPI-1 protein, the protein was located in the cell wall of elongating epicotyls and radicles by Western-blot experiments, in agreement with the transcription pattern. These results, together with the fact that both CaTPI-1 mRNA and protein levels decreased with epicotyl growth, suggest a possible role in the elongation of seedling epicotyls and radicles. Immunolocalization analyses of the TPI-1 protein indicated that it is abundant in the cell walls of both immature primary xylem cells and surrounding parenchyma cells. This location has led us to explore potential functions for TPI-1 protein in vascular tissue during seedling elongation.

Molecular Evolution of a Small Gene Family of Wound Inducible Kunitz Trypsin Inhibitors in Populus

Maximum likelihood models of codon substitutions were used to analyze the molecular evolution of a Kunitz trypsin inhibitor (KTI) gene family in Populus and Salix. The methods support previous assertions that the KTI genes comprise a rapidly evolving gene family. Models that allow for codon specific estimates of the ratio of nonsynonymous to synonymous substitutions (omega) among sites detect positive Darwinian selection at several sites in the KTI protein. In addition, branch-specific maximum likelihood models show that there is significant heterogeneity in omega among branches of the KTI phylogeny. In particular, omega is substantially higher following duplication than speciation. There is also evidence for significant rate heterogeneity following gene duplication, suggesting different evolutionary rates in newly arisen gene duplicates. The results indicate uneven evolutionary rates both between sites in the KTI protein and among different lineages in the KTI phylogeny, which is incompatible with a neutral model of sequence evolution.

Wound-inducible proteinase inhibitors in pepper. Differential regulation upon wounding, systemin, and methyl jasmonate

Seven small (approximately 6,000 D) wound-inducible proteinase inhibitor proteins were isolated from leaves of pepper (Capsicum annuum) plants that are members of the potato inhibitor II family. N-terminal sequences obtained indicated that the pepper leaf proteinase inhibitors (PLPIs) exhibit homology to two GenBank accessions that code for preproteins containing three isoinhibitors domains each that, when post-translationally processed, can account for the mixture of isoinhibitors that are reported herein from pepper leaves. A constitutive level of PLPI proteins was found in pepper leaves, and these levels increased up to 2.6-fold upon wounding of the lower leaves. Exposing intact plants to methyl jasmonate vapors induced the accumulation of PLPIs. Supplying excised young pepper plants with water through the cut stems induced PLPI proteins to levels higher than those found in intact plants, but with high variability. Supplying the excised plants with systemin did not result in an increase of PLPI levels that were statistically higher than levels found in excised plants. Gel-blot analyses of PLPI induction revealed the presence of two mRNA bands, having slightly different mobilities in agarose gels. Only the low M(r) mRNA is present in untreated control plants, and it appears to be responsible for the constitutive levels of PLPI found in leaves. Both mRNA species are wound- and methyl jasmonate-inducible. Only the low- M(r) species is weakly induced by systemin, indicating a differential expression of the two PLPI species.

Proteolytic activity in relation to seasonal cambial growth and xylogenesis in Pinus banksiana

Proteolytic activity in the cambial zone and developing xylem of Pinus banksiana Lamb. was investigated over an annual cycle of growth and dormancy. Highest proteolytic activity was associated with the most active period of primary-wall radial expansion of cambial derivatives, in early spring, before protoplasmic autolysis was initiated in developing earlywood. Three pH maxima of proteolytic activity, near pH 3.0, 6.5 and 9.5, were observed at that time. In general, activities measured at pH values below 7.0 were greater than those determined above pH 7.0 at all stages in the annual cycle, in both cambial zone and developing xylem, although elevated activity at alkaline pH was also observed during springtime growth. Polyvinylpolypyrollidone (PVP) treatment markedly enhanced pH 7.5 but not pH 4.0 proteolytic activity in the cambial zone, but not in developing xylem, indicating the presence of PVP-binding proteinase regulators in the cambium. By fractionation and effector studies total proteolysis was determined to comprise interactions between serine, cystine, aspartate and metallo-proteases having MWs, by gel chromatography, between 10 and 100 kDa. The observations point to a complex regulatory mechanism controlling the presence and catalytic rates of the distinct types of proteases in the cambial region throughout an annual cycle of growth and dormancy.

Systemin: a polypeptide signal for plant defensive genes

Damage to leaves of several plant species by herbivores or by other mechanical wounding induces defense gene activation throughout the plants within hours. An 18-amino acid polypeptide, called systemin, has been isolated from tomato leaves that is a powerful inducer of over 15 defensive genes when supplied to the tomato plants at levels of fmol/plant. Systemin is readily transported from wound sites and is considered to be the primary systemic signal. The polypeptide is processed from a 200-amino acid precursor called prosystemin, analogous to polypeptide hormones in animals. However, the plant prohormone does not possess typical dibasic cleavage sites, nor does it contain a signal sequence or any typical membrane-spanning regions. The signal transduction pathway that mediates systemin signaling involves linolenic acid release from membranes and subsequent conversion to jasmonic acid, a potent activator of defense gene transcription. The pathway exhibits analogies to arachidonic acid/prostaglandin signaling in animals that leads to inflammatory and acute phase responses.