MYC2 differentially modulates diverse jasmonate-dependent functions in Arabidopsis.

The Arabidopsis thaliana basic helix-loop-helix Leu zipper transcription factor (TF) MYC2/JIN1 differentially regulates jasmonate (JA)-responsive pathogen defense (e.g., PDF1.2) and wound response (e.g., VSP) genes. In this study, genome-wide transcriptional profiling of wild type and mutant myc2/jin1 plants followed by functional analyses has revealed new roles for MYC2 in the modulation of diverse JA functions. We found that MYC2 negatively regulates Trp and Trp-derived secondary metabolism such as indole glucosinolate biosynthesis during JA signaling. Furthermore, MYC2 positively regulates JA-mediated resistance to insect pests, such as Helicoverpa armigera, and tolerance to oxidative stress, possibly via enhanced ascorbate redox cycling and flavonoid biosynthesis. Analyses of MYC2 cis binding elements and expression of MYC2-regulated genes in T-DNA insertion lines of a subset of MYC2-regulated TFs suggested that MYC2 might modulate JA responses via differential regulation of an intermediate spectrum of TFs with activating or repressing roles in JA signaling. MYC2 also negatively regulates its own expression, and this may be one of the mechanisms used in fine-tuning JA signaling. Overall, these results provide new insights into the function of MYC2 and the transcriptional coordination of the JA signaling pathway.

Brazil and the development of international scientific biosafety testing guidelines for transgenic crops.

Under the umbrella of the International Organisation of Biological Control (IOBC), an international working group of public sector scientists entitled on "Transgenic Organisms in Integrated Pest Management and Biological Control" has been organized. The group will develop scientific principles and detailed scientific guidelines for biosafety testing of transgenic crops. The key elements of this project are: (1) An international initiative including expert scientists from leading research institutions in developed and developing countries; (2) coordination of the development and implementation of the guidelines as a dynamic process, which will include scientific and technical capacity building and communication among scientists and between scientists and policy makers; (3) rapid serial publication of sections of the guidelines as they are completed; and (4) rapid and timely revision of previously published sections. The guidelines will be constructed on a case-by-case basis and will have no regulatory legitimacy themselves.

The roles of adult and larval specialisations in limiting the occurrence of five species of Dacus (Diptera: tephritidae) in cultivated fruits.

The relative importance of adult preferences or specialisations of larval physiology in restricting the host range of five species of Dacine fruit flies (Diptera: Tephritidae) was examined, with particular emphasis on their utilization of cultivated fruits. The species; D. tryoni, D. jarvisi, D. cucumis, D. musae and D. cacuminatus differ widely in host range with D. tryoni being highly polyphagous while D. cacuminatus is virtually monophagous. Laboratory experiments showed that larvae of all species survived and developed in many cultivated fruits in which the specialists never occur in the field. By contrast the oviposition preferences and specificity of adult females differed widely between species. Female D. tryoni oviposited in most species of fruit. The specialised species; D. cucumis, D. musae and D. cacuminatus strongly preferred their usual hosts and would not oviposit in novel fruits even in the absence of the preferred host. In contrast, D. jarvisi consistently preferred its main native host but when this was not offered readily accepted cultivated fruits. These differences in preference are consistent with the pattern of infestation displayed by each species in the field. The study indicate that, in general, the occurrence of these species of Dacus in cultivated fruits is constrained more by the behavioural preferences of adult females than by larval specialisations. A genetic change in some aspect of host recognition or acceptance would be necessary for the specialised species to regularly infest cultivated fruits though no change in larval characteristics may be needed. As the types and concentrations of defensive secondary compounds may differ between native and cultivated fruits this conclusion cannot be extended to host shifts among native fruits.

Bacteria associated with four species of Dacus (Diptera: Tephritidae) and their role in the nutrition of the larvae.

The bacteria associated with Dacus tryoni (Froggatt), Dacus jarvisi (Tryon), Dacus neohumeralis (Hardy) and Dacus cacuminatus (Hering) were examined. Bacteria were isolated from the surface of freshly-laid eggs, from within surface sterilised pupae, from heads and abdomens of wild and laboratory-maintained flies, and from decomposed fruits in which the wild larvae were feeding. A more diverse flora was associated with D. tryoni and D. jarvisi (15 and 14 species, respectively) than with D. neohumeralis and D. cacuminatus (9 and 6 species, respectively). Most of the bacteria belonged to the family Enterobacteriaceae and while there were similarities of bacterial associations between fly species there was no evidence of a strict symbiotic association of a particular bacterium or bacteria with each species of fly. The larvae of D. jarvisi were unable to develop normally in an artificial medium containing unhydrolysed protein and free of bacteria and on a medium containing casein and Serratia liquefaciens (isolated from the flies and shown to secrete protease) the larvae died. On the same casein medium containing Enterobacter cloacae (isolated from the flies and shown to be protease negative) the larvae developed normally. Larvae of D. tryoni and D. jarvisi were devoid of protease and cellulase activity, but contained some amylase activity. The significance of these results in terms of current hypotheses concerning symbioses between tephritids and bacteria is discussed.

Oviposition behaviour of two tephritid fruit flies, Dacus tryoni and Dacus jarvisi, as influenced by the presence of larvae in the host fruit.

When offered a choice, females of the fruit flies Dacus tryoni (Frogg.) and D. jarvisi (Tryon) strongly preferred to lay in fruits without larvae rather than fruits which already contained larvae. Fruits which contained even low densities of larvae, including newly hatched ones, received many fewer eggs than control fruits. This preference was not influenced by the species of larvae present in the fruits nor by the distance to uninfested fruits. Discrimination occurred when fruits with and without larvae were close together (10 cm apart) and also when they were separated by distances of about one metre. Laboratory assays suggested that the flies detect chemical changes in the fruit associated with the decomposition which accompanies larval feeding, but they do not seem to detect the larvae Perse. This behaviour may be significant when these two species utilise the same host since the species which is able to infest fruits first will reduce the availability of hosts for the other species. In contrast to many other Tephritids (e.g. Rhagoletis, Anastrepha and Ceratitis) female Dacus don't discriminate against fruits which contain eggs nor do they deposit a pheromone to deter oviposition by females that subsequently visit the fruit. An hypothesis is proposed to explain the absence of oviposition-deterring pheromones in Dacus, and their presence in many other species of Tephritidae, on the basis of differences in life history and population structure.