Microbial Symbionts in Insects Influence Down-Regulation of Defense Genes in Maize

Diabrotica virgifera virgifera larvae are root-feeding insects and significant pests to maize in North America and Europe. Little is known regarding how plants respond to insect attack of roots, thus complicating the selection for plant defense targets. Diabrotica virgifera virgifera is the most successful species in its genus and is the only Diabrotica beetle harboring an almost species-wide Wolbachia infection. Diabrotica virgifera virgifera are infected with Wolbachia and the typical gut flora found in soil-living, phytophagous insects. Diabrotica virgifera virgifera larvae cannot be reared aseptically and thus, it is not possible to observe the response of maize to effects of insect gut flora or other transient microbes. Because Wolbachia are heritable, it is possible to investigate whether Wolbachia infection affects the regulation of maize defenses. To answer if the success of Diabrotica virgifera virgifera is the result of microbial infection, Diabrotica virgifera virgifera were treated with antibiotics to eliminate Wolbachia and a microarray experiment was performed. Direct comparisons made between the response of maize root tissue to the feeding of antibiotic treated and untreated Diabrotica virgifera virgifera show down-regulation of plant defenses in the untreated insects compared to the antibiotic treated and control treatments. Results were confirmed via QRT-PCR. Biological and behavioral assays indicate that microbes have integrated into Diabrotica virgifera virgifera physiology without inducing negative effects and that antibiotic treatment did not affect the behavior or biology of the insect. The expression data and suggest that the pressure of microbes, which are most likely Wolbachia, mediate the down-regulation of many maize defenses via their insect hosts. This is the first report of a potential link between a microbial symbiont of an insect and a silencing effect in the insect host plant. This is also the first expression profile for a plant attacked by a root-feeding insect

Biological Resource Management-Connecting Science and Policy TRANSGENIC CROPS: RECENT DEVELOPMENTS AND PROSPECTS

ABSTRACT It is now more than fifteen years since the first transgenic plants were generated experimentally. In that period there have been dramatic advances in our understanding on both basic and applied aspects of plant biology. Transgenic plant research depends on the availability of procedures for plant transformation. Two types of method for plant transformation exist, the use of Agrobacterium as a biological vector for foreign gene transfer, and direct gene transfer techniques, in which DNA is introduced into cells by the use of physical, electrical or chemical means. Agrobacterium can be used to transform a wide range of plants, but there are α number of species which are of interest for basic or applied research in which of Agrobacterium -mediated transformation is not reproducible or efficient. Using this procedures thousands of transgenic crops have been developed experimentally or field tested, while few of them are currently cultivated world wide, predominately on temperate zone crops and on conditions prevailing in industrial countries offering the potential increasing and improving food production capacity while limiting the use of agrochemicals and protect the environment. The " first generation " of transgenic crops were aimed at improving traits involving single genes. Now we are on the verge of a new step in crop modification, fueled by the rate at which new genes ( important for plant growth and development metabolism and stress tolerance ) characterised. Transgenic technology has been pivotal in the full spectrum of these new developments, from gene identification to an improved understanding of their regulation, as well as genetic transformation involving more complex transfers of many genes simultaneously. This will further help in managing natural resources like water, soil, e.t.c. in a better way. Our view of the nature of crop products can also be expected to change in the short to medium term, as plants are exploited for the production of novel compounds such as biodegradable plastics and new pharmaceuticals. However, it is the case that the extent to which the potential of transgenic research is realised will depend on public acceptance. To a significant extent this will require that the biology of transgenics is fully understood, and that a maximum degree of predictability of transgene effect, both phenotypic and genotypic, can be ensured. There is a need for diffusing this technology to tropical plants and adapt it to benefice the small farmer in the developing world were food demands will increase. To achieve this it requires: to find ways integrating biotechnology research into their national agricultural research activities in one hand horizontal and vertical networking cooperation on the other. Finally the implication of advancement in this relatively new technology especially in the area of biosafety, production patterns, biodiversity, inertecnal property rights and other critical factors should be sufficiently dismissed and understood