title: Field-Evolved Mode 1 Resistance of the Fall Armyworm to Transgenic Cry1Fa-Expressing Corn Associated with Reduced Cry1Fa Toxin Binding and Midgut Alkaline Phosphatase Expression.
abstract: Insecticidal protein genes from the bacterium Bacillus thuringiensis (Bt) are expressed by transgenic Bt crops (Bt crops) for effective and environmentally safe pest control. The development of resistance to these insecticidal proteins is considered the most serious threat to the sustainability of Bt crops. Resistance in fall armyworm (Spodoptera frugiperda) populations from Puerto Rico to transgenic corn producing the Cry1Fa insecticidal protein resulted, for the first time in the United States, in practical resistance, and Bt corn was withdrawn from the local market. In this study, we used a field-collected Cry1Fa corn-resistant strain (456) of S. frugiperda to identify the mechanism responsible for field-evolved resistance. Binding assays detected reduced Cry1Fa, Cry1Ab, and Cry1Ac but not Cry1Ca toxin binding to midgut brush border membrane vesicles (BBMV) from the larvae of strain 456 compared to that from the larvae of a susceptible (Ben) strain. This binding phenotype is descriptive of the mode 1 type of resistance to Bt toxins. A comparison of the transcript levels for putative Cry1 toxin receptor genes identified a significant downregulation (>90%) of a membrane-bound alkaline phosphatase (ALP), which translated to reduced ALP protein levels and a 75% reduction in ALP activity in BBMV from 456 compared to that of Ben larvae. We cloned and heterologously expressed this ALP from susceptible S. frugiperda larvae and demonstrated that it specifically binds with Cry1Fa toxin. This study provides a thorough mechanistic description of field-evolved resistance to a transgenic Bt crop and supports an association between resistance and reduced Cry1Fa toxin binding and levels of a putative Cry1Fa toxin receptor, ALP, in the midguts of S. frugiperda larvae.
authors.affiliation: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Siva R K
authors.initials: SRK
authors.lastname: Jakka
authors.affiliation: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Gong
authors.affiliation: Dow AgroSciences, Indianapolis, Indiana, USA.
authors.forename: James
authors.initials: J
authors.lastname: Hasler
authors.affiliation: Genome Science and Technology Graduate Program, University of Tennessee, Knoxville, Tennessee, USA.
authors.forename: Rahul
authors.initials: R
authors.lastname: Banerjee
authors.affiliation: Dow AgroSciences, Indianapolis, Indiana, USA.
authors.forename: Joel J
authors.initials: JJ
authors.lastname: Sheets
authors.affiliation: Dow AgroSciences, Indianapolis, Indiana, USA.
authors.forename: Kenneth
authors.initials: K
authors.lastname: Narva
authors.affiliation: Biology Department, University of New Mexico, Albuquerque, New Mexico, USA.
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Blanco
authors.affiliation: Department of Entomology and Plant Pathology, University of Tennessee, Knoxville, Tennessee, USA jurat@utk.edu.
authors.forename: Juan L
authors.initials: JL
authors.lastname: Jurat-Fuentes
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism*; D000818:Animals; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000633:toxicity*; D004731:Endotoxins / Q000235:genetics / Q000633:toxicity*; D041981:Gastrointestinal Tract / Q000187:drug effects / Q000201:enzymology; D006460:Hemolysin Proteins / Q000235:genetics / Q000633:toxicity*; D007305:Insecticide Resistance; D030821:Plants, Genetically Modified / Q000469:parasitology*; D011485:Protein Binding; D011647:Puerto Rico; D018411:Spodoptera / Q000187:drug effects* / Q000502:physiology; D014481:United States; D003313:Zea mays / Q000469:parasitology*
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D000469:Alkaline Phosphatase