Christiane Nardon

Effects of the cysteine protease inhibitor oryzacystatin (OC-I) on different aphids and reduced performance of Myzus persicae on OC-I expressing transgenic oilseed rape

Abstract When administered in artificial diets, the cysteine protease inhibitor (PI) oryzacystatin I (OC-I) induced moderate but significant growth inhibition on the pea aphid (Acyrthosiphon pisum Harris), the cotton/melon aphid (Aphis Gossypii Glover) and the peach potato aphid (Myzus persicae Sulzer). In transgenic oilseed rape plants (Brassica napus L. cv. Drakkar) expressing OC-I under the control of the CaMV-35S RNA promoter, oryzacystatin was detected in both leaves and phloem sap. Transgenic plants from three independent homozygous lines were used to test the effect of in planta-expression of OC-I on M. persicae. Mean adult weight and fecundity were significantly reduced, and aphid biomass produced in 2 weeks was decreased by 25–40% for aphids fed transgenic plants, when compared to those fed control plants. The effects of OC-I on M. persicae were correlated with the decrease of a major cathepsin L/H-type cysteine protease activity, detected in whole insect extracts. Immuno-histological analysis showed OC-I labeling along the gut epithelium, but also its association with aphid bacteriocytes and oenocytes. These results suggest that OC-I affects M. persicae through digestive tract targets, but also by reaching the haemolymph, thereby inhibiting extra-digestive proteolytic activities and interacting with functions related to aphid reproduction. Overall, it appears that PIs can display deleterious effects against phloem-feeding insects in addition to their activity on leaf-feeding insects.

Genome size characterization of the principal endocellular symbiotic bacteria of the weevil Sitophilus oryzae, using pulsed field gel electrophoresis

Abstract The chromosome size of the principal intracellular symbiotic bacteria (endocytobiotes) of the weevil Sitophilus oryzae has been determined by pulsed field gel electrophoresis (PFGE). The restriction enzymes SpeI, SwaI and XbaI generated 22, 23 and 24 fragments, respectively. The fragment sizes ranged from 15 to 460 kb and the genome size of the symbiotic bacteria was estimated to be approximately 3.0 Mb. An additional fragment was seen when running total undigested DNA and should correspond to a plasmid of 138 kb. The principal symbiotic bacteria belong to the enterobacteriaceae family and are closely related to Escherichia coli . The difference between the genome size of E. coli (4.7 Mb) and symbiotic bacteria (3.0 Mb) was discussed and might be related to the intracellular evolution of the endocytobiotes within their host. No more than two rDNA (23S) loci were found with I-CeuI digestion, which argues against a serial fragment gene deletion in the course of evolution.

Is genome size influenced by colonization of new environments in dipteran species

Genome size differences are usually attributed to the amplification and deletion of various repeated DNA sequences, including transposable elements (TEs). Because environmental changes may promote modifications in the amount of these repeated sequences, it has been postulated that when a species colonizes new environments this could be followed by an increase in its genome size. We tested this hypothesis by estimating the genome size of geographically distinct populations of Drosophila ananassae, Drosophila malerkotliana, Drosophila melanogaster, Drosophila simulans, Drosophila subobscura, and Zaprionus indianus, all of which have known colonization capacities. There was no strong statistical differences between continents for most species. However, we found that populations of D. melanogaster from east Africa have smaller genomes than more recent populations. For species in which colonization is a recent event, the differences between genome sizes do not thus seem to be related to colonization history. These findings suggest either that genome size is seldom modified in a significant way during colonization or that it takes time for genome size of invading species to change significantly.

WORLDWIDE DISTRIBUTION OF TRANSPOSABLE ELEMENT COPY NUMBER IN NATURAL POPULATIONS OF DROSOPHILA SIMULANS

Abstract.— Transposable elements (TEs), which promote various kinds of mutations, constitute a large fraction of the genome. How they invade natural populations and species is therefore of fundamental importance for understanding the dynamics of genetic diversity and genome composition. On the basis of 85 samples of natural populations of Drosophila simulans, we report the distributions of the genome insertion site numbers of nine TEs that were chosen because they have a low average number of sites. Most populations were found to have 0–3 insertion sites, but some of them had a significantly higher number of sites for a given TE. The populations located in regions outside Africa had the highest number of sites for all elements except HMS Beagle and Coral, suggesting a recent increase in the activity of some TEs associated with the colonization patterns of Drosophila simulans. The element Tirant had a very distinctive pattern of distribution: it was identified mainly in populations from East Africa and some islands in the Indian Ocean, and its insertion site number was low in all these populations. The data suggest that the genome of the entire species of Drosophila simulans may be being invaded by TEs from populations in which they are present in high copy number.

The role of symbiotes in flight activity of Sitophilus weevils

The flight activity (take‐off) of various strains of Sitophilus oryzae L. and S. zeamais Mots. (Coleoptera, Curculionidae) have been compared on wheat. It was shown that males are more active than females and that S. zeamais, is more active than S. oryzae. Furthermore, in the two species, when reared on wheat kernels, only symbiotic weevils were able to fly, while aposymbiotic insects did not. By supplementation of the diet with vitamins (pantothenic acid, riboflavin) and amino acids (phenylalanine and proline), this activity could be restored in part. The influence of symbiosis on the flight ability of Sitophilus weevil is discussed in relation to the energy metabolism (coenzymes, proline), the role played by symbiosis in this behaviour and its possible effect on the dissemination of the species.

Variation of the Genome Size Estimate With Environmental Conditions in Drosophila melanogaster

Genome size is known to exhibit interspecies differences, but also to vary between populations within a given species and even between individual cells within an organism. Major differences have often been reported and attributed to differences in measurement conditions, in internal controls of genome size, and in the stains used. Flow cytometry using intercalating dyes is the most attractive method for measuring genome size.

Storage proteins in coleoptera: A new class of tyrosine-rich proteins from the pupae of two weevils, Sitophilus oryzae and Rhynchophorus palmarum (Coleoptera: Curculionidae)

Abstract The occurrence of tyrosine-rich storage proteins was investigated in two weevils (Coleoptera: Curculionidae). Three monomers (two major, 44 and 31 kDa, and one minor, 51 kDa) were purified from pupae of Sitophilus oryzae , and one major monomer (65 kDa) from Rhynchophorus palmarum . These related proteins belong to a new class of insect storage proteins, different from either arylphorin or other identified storage proteins. They occur as insoluble granules in the pupal fat body, and are only extracted by denaturing conditions such as 1% SDS or 8 M urea. A convenient tyrosine-specific stain was adapted to track them easily during the purification process, which involved preparative SDS-PAGE. The monomers contained no lipids, no phosphate groups and their glycoprotein nature is uncertain. According to their amino acid compositions, these proteins may be divided into two subclasses: all of them yield three predominant amino acids amounting to more than 15% of the total amino acids each (tyrosine, serine and glycine), but the smaller So31 polypeptide exhibits and exceptionally high tyrosine content (more than 27%). The presence of arylphorin in Curculionid hemolymph was investigated, and the comparative features of these two classes of tyrosine-rich proteins are discussed.

A new technique to immobilize an aphid or a mealybug on plants using a high-frequency microcautery unit

Light microscopy is the oldest tool used to describe stylet pathways of homopterous insects within their host plant. Since 1960, electrical recording of penetration behaviour by aphids has been introduced by McLean & Kinsey (1967) and modified from an AC to a DC device called the electrical penetration graph technique (EPG) by Tjallingii (1978). EPG, especially when combined with microscopy, is unique in describing the details of penetration activity, and in studying the feeding behaviour of phloem- or xylem-feeding insects.

Characteristics and development of the tyrosine-rich protein granules in the adipose tissue of the curculionid beetle Sitophilus oryzae

In the Curculionid beetle Sitophilus oryzae, the fat body is composed of one type of adipocyte, interstitial cells and oenocytes. Synthesis and storage of tyrosine-rich-protein granules (TRPG) in adipocytes are observed during all the larval and prepupal stages (except the first larval instar which has not been studied). They appear first in the posterior part of the fat body, around the nucleus of adipocytes. They progressively invade the cytoplasm. In the young pupa, TRPG are present in every part of the body, including the head and the appendages in formation. TRPG grow in size by fusing together. Their mean diameter is 6 microm, but some of them reach up to 50 microm. They present a basic core and an acidic periphery. Their charge in tyrosine increases until the prepupa. They are APS and lipid negative and contain no RNA. During metamorphosis they take on a reticulated structure, evoking a golf ball, and disintegrate into small granules, the tyrosine content of which diminishes drastically, especially in contact with epidermal cells, whence tyrosine is probably transferred. TRPG in S. oryzae contain 16 different insoluble proteins. Five of them are tyrostaurins characterized by their very high content in tyrosine (up to 27%) and their strict insolubility in aqueous solution. Arylphorin-like proteins have not been detected in S. oryzae granules.