Transcriptional responses underlying the hormetic and detrimental effects of the plant secondary metabolite gossypol on the generalist herbivore Helicoverpa armigera

<p>Abstract</p> <p>Background</p> <p>Hormesis is a biphasic biological response characterized by the stimulatory effect at relatively low amounts of chemical compounds which are otherwise detrimental at higher concentrations. A hormetic response in larval growth rates has been observed in cotton-feeding insects in response to increasing concentrations of gossypol, a toxic metabolite found in the pigment glands of some plants in the family Malvaceae. We investigated the developmental effect of gossypol in the cotton bollworm, <it>Helicoverpa armigera</it>, an important heliothine pest species, by exposing larvae to different doses of this metabolite in their diet. In addition, we sought to determine the underlying transcriptional responses to different gossypol doses.</p> <p>Results</p> <p>Larval weight gain, pupal weight and larval development time were measured in feeding experiments and a hormetic response was seen for the first two characters. On the basis of net larval weight gain responses to gossypol, three concentrations (0%, 0.016% and 0.16%) were selected for transcript profiling in the gut and the rest of the body in a two-color double reference design microarray experiment. Hormesis could be observed at the transcript level, since at the low gossypol dose, genes involved in energy acquisition such as β-fructofuranosidases were up-regulated in the gut, and genes involved in cell adhesion were down-regulated in the body. Genes with products predicted to be integral to the membrane or associated with the proteasome core complex were significantly affected by the detrimental dose treatment in the body. Oxidoreductase activity-related genes were observed to be significantly altered in both tissues at the highest gossypol dose.</p> <p>Conclusions</p> <p>This study represents the first transcriptional profiling approach investigating the effects of different concentrations of gossypol in a lepidopteran species. <it>H. armigera</it>'s transcriptional response to gossypol feeding is tissue- and dose-dependent and involves diverse detoxifying mechanisms not only to alleviate direct effects of gossypol but also indirect damage such as pH disturbance and oxygen radical formation. Genes discovered through this transcriptional approach may be additional candidates for understanding gossypol detoxification and coping with gossypol-induced stress. In a generalist herbivore that has evolved transcriptionally-regulated responses to a variety of different plant compounds, hormesis may be due to a lower induction threshold of growth-promoting, stress-coping responses and a higher induction threshold of detoxification pathways that are costly and cause collateral damage to the cell.</p

Effect of cotton cultivars on the oviposition preference of pink bollworm (Lepidoptera: Gelechiidae)

The effect of four cotton cultivars on the oviposition behavior of the pink bollworm Pectinophora gossypiella (Saunders) was studied under laboratory and semi-field conditions. Young plants and bolls from four commercial upland cotton cultivars (Lachata, Macnair-220, Midas and Sandra) cultivated in the area of Thessaloniki were used. The four cultivars had palmate leaves, and nectaries on both leaves and bolls. Differences were observed in the trichome density and the length of leaf petiole among the cultivars. The typical shape of bolls was either round or ovate. Differences were observed among the cultivars tested in boll size and bract's length. In a series of experiments we recorded the number of eggs oviposited in no-, two-, three-, and four-choice tests using either young plants or bolls. Although the four cotton cultivars exhibited a variation in morphological characteristics, the mean number of eggs oviposited on young plants and bolls did not differ among them in two-, three-, and four-choice experiments. Substantially higher number of eggs were oviposited on either young plants or bolls of Midas in no-choice experiments. Eggs were oviposited mainly on newly developed unfolded leaves of the young plants and under the calyx of the bolls. In a semi-field experiment, we found a clear oviposition preference for bolls compared with plant terminals in all the cultivars tested. Females oviposited similar number of eggs in the four cultivars. We discuss the effect of morphological characteristics of cotton cultivars on the oviposition behavior of pink bollworm