Do legume storage proteins play a role in defending seeds against bruchids?

Dietary specialization in European species groups of seed beetles (Coleoptera: Bruchidae: Bruchinae)

Because of their particular biology, seed beetles exhibit a strong relationship with their larval host plants. In Europe, however, field data have long been scarce and unreliable. The results of Legume seed collections of nearly 1,000 samples belonging to 292 species from various locations in Europe are summarized. The status of current Bruchidius species groups is amended on morphological and phylogenetic bases. Recent advances in the knowledge of phylogenetic structures of both Fabaceae and Bruchinae provide a new picture of Bruchinae-Fabaceae interactions. It reveals a certain level of host conservatism. The hypothesis of radiative adaptation seems the most compatible with observed data.

Presence of the storage seed protein vicilin in internal organs of larval Callosobruchus maculatus (Coleoptera: Bruchidae)

Variant vicilins (7S storage globulins) of cowpea seeds (Vigna unguiculata) are considered as the main resistance factor present in some African genotypes against the bruchid Callosobruchus maculatus. It has been suggested that the toxic properties of vicilins may be related to their recognition and interaction with glycoproteins and other membrane constituents along the digestive tract of the insect. However, the possibility of a systemic effect has not yet been investigated. The objective of this work was to study the fate of 7S storage globulins of V. unguiculata in several organs of larvae of the cowpea weevil C. maculatus. Results demonstrated binding of vicilins to brush border membrane vesicles, suggesting the existence of specific receptors. Vicilins were detected in the haemolymph, in the midgut, and in internal organs, such as fat body and malpighian tubules. There is evidence of accumulation of vicilins in the fat body of both larvae and adults. The absorption of vicilins and their presence in insect tissues parallels classical sequestration of secondary compounds.

Performance of bean bruchids Callosobruchus maculatus and Zabrotes subfasciatus (Coleoptera: Bruchidae) reared on resistant (IT81D-1045) and susceptible (Epace 10) Vigna unguiculata seeds: Relationship with trypsin inhibitor and vicilin excretion

Callosobruchus maculatus (Cm) and Zabrotes subfasciatus (Zs) were reared on resistant (IT81D-1045) and on susceptible (Epace 10) cowpea seeds. The emergence of adult insects, total developmental period (TDP) and excretion of trypsin inhibitor and vicilin were determined for both bruchid populations. Parameter evaluation showed that the Zs populations emerged from both seeds had no significant differences in emergence and TDP. The Cm population raised from resistant seeds had lower emergence (5.6+/-1.3%) and delayed TDP (46+/-1.25 days) than those emerged from susceptible seeds. The excretion of defense proteins showed that Zs reared in resistant seeds excreted 1.7 times more trypsin inhibitor, but this did not affect emergence or TDP. Furthermore, Cm population emerged from resistant seeds excreted 7 times higher vicilin and 0.4 times less trypsin inhibitor than that emerged from susceptible seeds. These results indicate that vicilins from resistant seeds are involved to significantly longer TDP (46 days) and also drastic reduction of insect emergence ( approximately 5%) of C. maculatus.

Detection of single nucleotide polymorphisms in 24 kDa dimeric α-amylase inhibitors from cultivated wheat and its diploid putative progenitors

Seventeen new genes encoding 24 kDa family dimeric alpha-amylase inhibitors had been characterized from cultivated wheat and its diploid putative progenitors. And the different alpha-amylase inhibitors in this family, which were determined by coding regions single nucleotide polymorphisms (cSNPs) of their genes, were investigated. The amino acid sequences of 24 kDa alpha-amylase inhibitors shared very high coherence (91.2%). It indicated that the dimeric alpha-amylase inhibitors in the 24 kDa family were derived from common ancestral genes by phylogenetic analysis. Eight alpha-amylase inhibitor genes were characterized from one hexaploid wheat variety, and clustered into four subgroups, indicating that the 24 kDa dimeric alpha-amylase inhibitors in cultivated wheat were encoded by multi-gene. Forty-five cSNPs, including 35 transitions and 10 transversions, were found, and resulted in a total of ten amino acid changes. The cSNPs at the first site of a codon cause much more nonsynonymous (92.9%) than synonymous mutations, while nonsynonymous and synonymous mutations were almost equal when the cSNPs were at the third site. It was observed that there was Ile105 instead of Val105 at the active region Val104-Val105-Asp106-Ala107 of the alpha-amylase inhibitor by cSNPs in some inhibitors from Aegilops speltoides, diploid and hexaploid wheats.

A reproducible genetic transformation system for cultivated Phaseolus acutifolius (tepary bean) and its use to assess the role of arcelins in resistance to the Mexican bean weevil

A reproducible Agrobacterium tumefaciens-mediated genetic transformation method that delivers fertile and morphologically normal transgenic plants was developed for cultivated tepary bean (Phaseolus acutifolius L. Gray). Factors contributing to higher transformation efficiencies include (1) a low initial concentration of bacteria coupled with a longer cocultivation period with callus, (2) an initial selection of callus on a medium containing low levels of the selectable agent, (3) omission of the selectable agent from the medium during callus differentiation to shoots and (4) the efficient conversion of transgenic shoots into fertile plants. All plants regenerated with this procedure (T0) were stably transformed, and the introduced foreign genes were inherited in a Mendelian fashion in most of the 33 independent transformants. Integration, stable transmission and high expression levels of the transgenes were observed in the T1 and/or T3 progenies of the transgenic lines. The binary transformation vectors contained the beta-glucuronidase reporter gene, the neomycin phosphotransferase II selectable marker gene and either an arcelin 1 or an arcelin 5 gene. Arcelins are seed proteins that are very abundant in some wild P. vulgaris L. genotypes showing resistance to the storage insect Zabrotes subfasciatus (Boheman) (Coleoptera, Bruchidae). Transgenic beans from two different cultivated P. acutifolius genotypes with high arcelin levels were infested with Z. subfasciatus, but they were only marginally less susceptible to infestation than the non-transgenic P. acutifolius. Hence, the arcelin genes tested here are not major determinants of resistance against Z. subfasciatus.

The seed coat of Phaseolus vulgaris interferes with the development of the cowpea weevil [Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)]

We have confirmed here that the seeds of the common bean (Phaseolus vulgaris, L.) do not support development of the bruchid Callosobruchus maculatus (F.), a pest of cowpea [Vigna unguiculata (L.) Walp] seeds. Analysis of the testa (seed coat) of the bean suggested that neither thickness nor the levels of compounds such as tannic acid, tannins, or HCN are important for the resistance. On the other hand, we have found that phaseolin (vicilin-like 7S storage globulin), detected in the testa by Western blotting and N-terminal amino acid sequencing, is detrimental to the development of C. maculatus. As for the case of other previously studied legume seeds (Canavalia ensiformis and Phaseolus lunatus) we suggest that the presence of vicilin-like proteins in the testa of P. vulgaris may have had a significant role in the evolutionary adaptation of bruchids to the seeds of leguminous plants.

Cowpea (Vigna unguiculata) vicilins bind to the peritrophic membrane of larval sugarcane stalk borer (Diatraea saccharalis)

In this work, we show that vicilins from two Vigna unguiculata (cowpea) genotypes, Epace-10 and IT 81D-1045, which are susceptible and resistant to attack by the cowpea weevil Callosobruchus maculatus, respectively, associate with the peritrophic membrane (PM) from larvae of Diatraea saccharalis. Solutions with increasing concentrations of vicilins were incubated with PM of the larvae and subsequently analysed by electrophoresis with SDS. It was observed that the majority of the bands of approximately 50,000 Da (characteristic of vicilins) did not appear in the separating gel and only lower molecular weight polypeptides were seen. When vicilins were incubated with PM, and the solution was then heated after the incubation, the band pattern in the gel appeared completely different. It was observed that the vicilins were being hydrolysed by proteinases associated with the PM. When the incubated samples were heated after the reaction, the major bands reappeared, demonstrating that most of the vicilin molecules had bound to the PM of D. saccharalis. These results suggest that when the vicilins are in contact with the PM they are bound and also digested by the PM of this insect. The major and several minor proteinases from the PM were extracted with Triton X-100 and their activity and the inhibition of this activity were analysed by ingel assays. Based on the effects of proteinase inhibitors, the PM-associated activity is due to serine class proteinases. Larvae of D. saccharalis were fed on artificial diets containing purified vicilins from Epace-10 or IT 81D-1045 seeds. Vicilins from Epace-10 did not affect the larval development, while IT 81D-1045 vicilins reduced significantly the survival rate of the sugar cane borer.

Plant insulin or glucokinin: a conflicting issue

The presence of insulin in plants is not accepted by the scientific community in general. In this review we discuss this paradigm and retrieve information that strongly suggests that insulin is indeed found in plants. We present results, which indicate that a protein molecule with the same amino acid sequence as bovine insulin is expressed in leguminous plants. Additionally, we provide evidence that proteins associated with insulin signalling pathways in vertebrates are also found in association with insulin-like molecules in plants.

Plant toxic proteins with insecticidal properties. A review on their potentialities as bioinsecticides

To meet the demands for food of the expanding world population, there is need of new ways for protecting plant crops against predators and pathogens while avoiding the use of environmentally aggressive chemicals. A milestone in this field was the introduction into crop plants of genes expressing Bacillus thuringiensis entomotoxic proteins. In spite of the success of this new technology, however, there are difficulties for acceptance of these 'anti-natural' products by the consumers and some concerns about its biosafety in mammals. An alternative could be exploring the plant's own defense mechanisms, by manipulating the expression of their endogenous defense proteins, or introducing an insect control gene derived from another plant. This review deals with the biochemical features and mechanisms of actions of plant proteins supposedly involved in defense mechanisms against insects, including lectins, ribosome-inactivating proteins, enzymes inhibitors, arcelins, chitinases, ureases, and modified storage proteins. The potentialities of genetic engineering of plants with increased resistance to insect predation relying on the repertoire of genes found in plants are also discussed. Several different genes encoding plant entomotoxic proteins have been introduced into crop genomes and many of these insect resistant plants are now being tested in field conditions or awaiting commercialization.

Plant-insect interactions: an evolutionary arms race between two distinct defense mechanisms

In this review, plant-insect interaction is discussed as a dynamic system, subjected to continual variation and change. Plants developed different mechanisms to reduce insect attack, including specific responses that activate different metabolic pathways which considerably alter their chemical and physical aspects. On the other hand, insects developed several strategies to overcome plant defense barriers, allowing them to feed, grow and reproduce on their host plants. This review foccuses on several aspects of this complex interaction between plants and insects, including chemical-derived substances, protein-derived molecules and volatile compounds of plants whereas metabolization, sequestration or avoidance are in turn employed by the insects.

Plant alpha-amylase inhibitors and their interaction with insect alpha-amylases

Insect pests and pathogens (fungi, bacteria and viruses) are responsible for severe crop losses. Insects feed directly on the plant tissues, while the pathogens lead to damage or death of the plant. Plants have evolved a certain degree of resistance through the production of defence compounds, which may be aproteic, e.g. antibiotics, alkaloids, terpenes, cyanogenic glucosides or proteic, e.g. chitinases, beta-1,3-glucanases, lectins, arcelins, vicilins, systemins and enzyme inhibitors. The enzyme inhibitors impede digestion through their action on insect gut digestive alpha-amylases and proteinases, which play a key role in the digestion of plant starch and proteins. The natural defences of crop plants may be improved through the use of transgenic technology. Current research in the area focuses particularly on weevils as these are highly dependent on starch for their energy supply. Six different alpha-amylase inhibitor classes, lectin-like, knottin-like, cereal-type, Kunitz-like, gamma-purothionin-like and thaumatin-like could be used in pest control. These classes of inhibitors show remarkable structural variety leading to different modes of inhibition and different specificity profiles against diverse alpha-amylases. Specificity of inhibition is an important issue as the introduced inhibitor must not adversely affect the plant's own alpha-amylases, nor the nutritional value of the crop. Of particular interest are some bifunctional inhibitors with additional favourable properties, such as proteinase inhibitory activity or chitinase activity. The area has benefited from the recent determination of many structures of alpha-amylases, inhibitors and complexes. These structures highlight the remarkable variety in structural modes of alpha-amylase inhibition. The continuing discovery of new classes of alpha-amylase inhibitor ensures that exciting discoveries remain to be made. In this review, we summarize existing knowledge of insect alpha-amylases, plant alpha-amylase inhibitors and their interaction. Positive results recently obtained for transgenic plants and future prospects in the area are reviewed.