Rickettsial symbionts of the genus Wolbachia, harboured by many arthropod species, are implicated in feminization, cytoplasmic incompatibility and parthenogenesis phenomena. These symbionts induce thelytokous parthenogenesis in some egg parasitoids of the Trichogramma genus. In our study of these minute wasps, puri¢ed Wolbachia from an infected species, T. pretiosum, were transferred by microinjection into in vitro developed pupae of an uninfected species,T. dendrolimi. We believe this to be the ¢rst successful transfer of Wolbachia in parasitoids. The presence or absence of Wolbachia was determined using DAPI staining, PCR and ftsZ gene sequencing. An ftsZ gene fragment from microinjected T. dendrolimi was shown to be identical to that of T. pretiosum, con¢rming that transfer was successful. Wolbachia were still present in the recipient species 26 generations after the transfer, although only partial induction of thelytoky was observed. Therefore, in Trichogramma, density of symbionts or symbiont^host interactions may be involved in the expression of parthenogenesis. The successful transfer of the symbiont within the Trichogrammatidae, a group of insects used in biological control strategies, could increase their agronomic importance by manipulating their reproductive system.

No abstract

Gryllus bimaculatus were infected with an intracellular prokaryote, Rickettsiella grylli, then reared either at fixed temperatures or in a temperature gradient (22-36 degrees C) where they could select the temperature they preferred. Only 50% of the infected insects reared at 28 degrees C or less survived after 20 days, against 75% of those reared at 30 degrees C or more and 90% of those in the temperature gradient. Examination of smears of insect tissue showed that all (100%) of the infected insects reared between 23 and 29 degrees C had developed a strong rickettsial infection. Only 20% of the insects reared in a gradient of temperature showed signs of strong infection. Body temperature of crickets in the temperature gradient, recorded using thin thermocouples, was 33 degrees C in infected crickets and 26.6 degrees C in controls. It is concluded that thermoregulatory behavior was used by the insects to produce a fever when infected with Rickettsiella grylli. This protected them and increased survival capacity.

No abstract

No abstract

Cauliflower mosaic virus (CaMV) aphid transmission factor (ATF or P18) is presumed to interact with both virus particles and vector mouthparts, thereby mediating virus aphid transmission. We developed a protein-protein binding assay and our results clearly show that virus particles bind strongly and specifically to P18 whether P18 was obtained from plants, a baculovirus expression system, or the pGEX-3X Escherichia coil expression system. We overproduced, using the pGEX-3X expression system, various fragments of P18 and thereby demonstrated that the C-terminal 31 amino acid residues are responsible for the interaction. Using PCR-based mutagenesis, 2 amino acid residues essential for interaction were identified. Point substitutions (amino adds 157 from Ile to Asn or 159 from Gly to Ser) were sufficient to abolish the interaction, whereas another mutation (amino acid 158 from He to Ser) had no effect on P18 virus binding. We evaluated whether there was a correlation between the ability of P18 to interact with CaMV particles and its biological activity. Aphid transmission assays were carried out and we demonstrated that the loss of the virus binding capacity had a dramatic effect on the ability of P18 to mediate aphid transmission. Thus, our results suggest that binding between P18 and virus particles is likely to be one ofthe molecular mechanisms involved in CaMV aphid transmission.

We analyzed the distribution of the caulif lower mosaic virus (CaMV) aphid transmission factor (ATF), produced via a baculovirus recombinant, within Sf9 insect cells. Immunogold labeling revealed that the ATF colocalizes with an atypical cytoskeletal network. Detailed observation by electron microscopy demonstrated that this network was composed of microtubules decorated with paracrystalline formations, characteristic of the CaMV ATF. A derivative mutant of the ATF, unable to self-assemble into paracrystals, was also analyzed. This mutant formed a net-like structure, with a mesh of four nanometers, tightly sheathing microtubules. Both the ATF-and the derivative mutant-microtubule complexes were highly stable. They resisted dilution-, cold-, and calcium-induced microtubule disassembly as well as a combination of all three for over 6 hr. CaMV ATF cosedimented with microtubules and, surprisingly, it bound to Taxol-stabilized microtubules at high ionic strength, thus suggesting an atypical interaction when compared with that usually described for microtubule-binding proteins. Using immunof luorescence double labeling we also demonstrated that the CaMV ATF colocalizes with the microtubule network when expressed in plant cells.Cauliflower mosaic virus (CaMV) was the first DNA plant virus to be reported (1); it is the type member of the genus Caulimovirus and is characterized by icosahedral particles 50 nm in diameter. The complete genome is a double-stranded circular DNA of Ϸ8000 bp encoding at least six genes which are believed to be independently translated from a full genome length polycystronic 35S RNA (for a review, see ref.2).CaMV is transmitted between host plants by several aphid species in a noncirculative manner (ref. 3; for a review about plant virus vector transmission, see refs. 4 and 5). After acquisition from an infected plant, the virus does not circulate within the vector's body and is retained for a relatively short time (few hours), probably on the cuticular lining of the aphid feeding apparatus. During subsequent feeding on a healthy plant, the virus is released to initiate a new infection. Lung and Pirone (6, 7) demonstrated that aphid transmission is regulated by an aphid transmission factor (ATF) that has been identified as the expression product of CaMV gene II (8-11). The ATF is a nonstructural polypeptide of 18 kDa (P18) and appears to have no other function in the CaMV life cycle. Indeed, isolate CM4-184, a naturally occurring mutant which completely lacks gene II, is infectious in host plants but is not aphid transmissible (12).Gene II of an aphid-transmissible CaMV isolate has been expressed to produce P18 in Sf9 insect cells via a baculovirus recombinant (13), which is biologically active (14). P18 and the virus can be acquired separately; aphids that are first fed through a parafilm membrane with baculovirus expressed P18 become capable of transmitting the naturally non-aphidtransmissible CM4-184 isolate. Native P18 accumulates, both in baculovirus recombinant-infected Sf9 cells ...

When in genetic females external male characters differentiate, the phenomenon is called "male pseudohermaphroditism." This male differentiation occurs in terrestrial isopods (Crustacea, suborder Oniscoidea) and sometimes involves only some epithelial areas (gynandromorphous mosaics). It is not induced by male hormones or by abnormal ovary function. This intersexuality is transmitted maternally (by the intersex females) or paternally (by the brothers of intersex females) to between 30% and 60% of their offspring.Although it occurs at 20TC, the male differentiation disappears when breeding takes place at 27TC. Male characters differentiate in normal females -ven in other Oniscoidea species (Porcefilo dilatatus, Porcellio laevis, Armadilidium vulgare)-after injection of a 0.22-jzm filtered tissue extract. Since an inhibitor of bacterial protein synthesis (gentamycin) does not inhibit this masculinizing effect, we infer that neither organelles nor bacteria are involved. Intersexuality is always correlated with the presence of cytoplasmic viral particles in both intersex-female and transmitter-male tissues. Striking similarities to the Drosophila S virus are noted. A reovirus-like Oniscoidea masculinizing virus, which probably acts only on the epithelial areas sensitive to the male hormones, is most likely the causative agent of this intersexuality. Here we report the conversion of secondary sexual characters putatively caused by a virus.In various species of Crustacea (a large class of Arthropoda)-especially in the terrestrial isopods (order Isopoda, suborder Oniscoidea)-some individuals exhibit sexual characteristics corresponding to the definition of external male pseudohermaphroditism (1,2). Physiological and genetic studies in Porcellio dilatatus have shown that these intersex individuals are genetic functional females having both male external characters and normal ovaries. In some intersexes such external masculinization is minimal, but in others it may be highly developed and as complete as in a male. Frequently, this masculinization is asymmetric, and external morphology is the same as exhibited by gynandromorphous mosaic individuals. However, this intersex morphology may change with age, and modifications in the localization of masculinized appendixes may occur after moulting. The masculinizing phase may go on for a few months or persist throughout the 2 or 3 years of their life. Such modifications of the secondary sexual characters, observed in female crustaceans, involve the male hormonal system. However, in the intersexes the male external differentiation is not induced by male hormone, since intersex females have no androgenic gland; moreover, intersexuality is not caused by abnormal ovarian function, since it persists in ovariectomized females. In fact, these male external characters appear in normal females when they are implanted with any organ from an intersex female (ovary, nervous tissue, adipose tissue, intestinal tissue) (3).Genetic studies have shown that masculinizing intersexuality m...