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Fitness costs of resistance to Bacillus thuringiensis (Bt) toxins can delay or counter the evolution of insect resistance to transgenic Bt crops. Here we tested the hypothesis that the plant defensive compound gossypol in cottonseed increases costs associated with resistance to Bt toxin Cry1Ac in pink bollworm (Pectinophora gossypiella), a cosmopolitan pest that feeds primarily on cottonseed. Previous work showed pink bollworm resistance to Cry1Ac produced by Bt cotton is associated with mutations disrupting a gene encoding a cadherin protein that binds Cry1Ac in susceptible larvae. We used larvae from two strains of pink bollworm, each harboring an intermediate frequency of a different cadherin allele linked with resistance. We tested larvae from both strains on two types of non-Bt cotton that differed nine-fold in the gossypol concentration in their seeds: a transgenic cultivar engineered for low gossypol production and its untransformed parental cultivar. After 10 days of larval feeding on bolls, the resistance allele frequency was significantly lower in larvae from the conventional cotton than transgenic cotton. These results imply the higher gossypol concentration in the conventional cottonseed increased the fitness cost affecting survival. Using a population genetics model, we estimated this increase in survival cost was at least 32%. We also detected a recessive fitness cost reducing larval weight in both strains of pink bollworm that did not differ between the two cotton cultivars. Designing insecticidal crops and refuge plants that exploit the vulnerability of resistant insects to plant defensive compounds could improve resistance management. • High gossypol concentration in cottonseed selected against resistance to Bt cotton in pink bollworm. • High gossypol concentration increased the survival cost of resistance to Bt cotton. • High gossypol concentration did not change the cost on development time. • Manipulating gossypol content of cottonseed could enhance pink bollworm resistance management. [ABSTRACT FROM AUTHOR]

Gossypol, a naturally occurring terpenoid found in pigment glands located throughout the cotton plant, is an effective insect deterrent, but is also a cumulative toxin in simple-stomached animals. Plant biotechnology utilizing RNAi was used to create a plant that has no gossypol in the seed while retaining gossypol in all other plant tissues to prevent predation. Since cotton is drought and heat tolerant, it is well suited to serve as a source of both food and fiber as climate change puts other crops in jeopardy. Agrobacterium transformation was used to insert into the cotton nuclear genome a construct containing a seed specific promoter driving an RNAi hairpin that suppresses delta-cadinene synthase. This enzyme plays a critical role early in building gossypol. This biotechnology-based proof of concept provides strong evidence that it is possible to produce a plant that retains its natural defense mechanism in the non-seed tissues while producing a drought and heat tolerant source of protein in the gossypol-free cottonseed. The presence of Gossypol in cotton seed means all the protein produced by the cotton plant is relegated to ruminant feed and (in miniscule amounts) aquacultre. Recent research demonstrates 100% replacement of fishmeal with Ultra-Low Gossypol Cottonseed (ULGCS) in the feeds of several aquaculture species without a decrease in performance. Each year about 10-11 million metric tons of cottonseed protein are produced worldwide. Without gossypol, this is enough protein to satisfy the daily, basic protein needs (50 grams/person) of more than 600 million people for one year. Food scientists have also created a wide range of food products from ULGCS, including hummus, plant-based dairy substitutes, a peanut butter alternative and protein fortified beverages. Elimination of gossypol in cottonseed could greatly improve utilization of this valuable protein resource for global food and fiber security as we move into an era of uncertain climate conditions. [ABSTRACT FROM AUTHOR]

Abstract: We have observed a novel, lesion mimic phenotype (LMP) in the cotyledons of cotton seedlings expressing an endochitinase gene from Trichoderma virens. This phenotype, however, is conditional and is elicited only when the transgenic seedlings are germinating on a medium that is devoid of mineral nutrients. The LMP manifests itself around the 5th day in the form of scattered, dry necrotic lesions on the cotyledons. The severity of the LMP is correlated with the level of transgene activity. Production of reactive oxygen species and activities of certain defense related enzymes and genes were substantially higher in the cotyledons of seedlings that were growing under mineral nutrient stress. Molecular and biochemical analyses indicated significantly higher-level activities of certain defense-related genes/enzymes at the onset of the phenotype. Treatment with methyl jasmonate can induce LMP in the cotyledons of wild-type (WT) seedlings similar to that observed in the endochitinase-expressing seedlings grown on nutrient-free medium. On the other hand, salicylic acid (SA), its functional analog, benzo(1,2,3) thiadiazole-7-carbothioic acid (BTH), and ibuprofen can rescue the LMP induced by the seedling-growth on nutrient-deficient medium. Nutrient deficiency-induced activation of a defense response appears to be the contributing factor in the development of LMP in endochitinase-expressing cotton seedlings. [Copyright &y& Elsevier]