title: Transcriptional response of soybean to thiamethoxam seed treatment in the presence and absence of drought stress.
abstract: BACKGROUND
  Neonicotinoid insecticides are widely known for their broad-spectrum control of arthropod pests. Recently, their effects on plant physiological mechanisms have been characterized as producing a stress shield, which is predicted to enhance tolerance to adverse conditions. Here we investigate the molecular underpinnings of the stress shield concept using the neonicotinoid thiamethoxam in two separate experiments that compare gene expression. We hypothesized that the application of a thiamethoxam seed treatment to soybean would alter the expression of genes involved in plant defensive pathways and general stress response in later vegetative growth. First, we used next-generation sequencing to examine the broad scale transcriptional effects of the thiamethoxam seed treatment at three vegetative stages in soybean. Second, we selected ten target genes associated with plant defense pathways in soybean and examined the interactive effects of thiamethoxam seed treatment and drought stress on expression using qRT-PCR.
  
  
  RESULTS
  Direct comparison of thiamethoxam-treated and untreated soybeans revealed minor transcriptional differences. However, when examined across vegetative stages, the thiamethoxam seed treatment induced substantial transcriptional changes that were not observed in untreated plants. Genes associated with photosynthesis, carbohydrate and lipid metabolism, development of the cell wall and membrane organization were uniquely upregulated between vegetative stages in thiamethoxam-treated plants. In addition, several genes associated with phytohormone and oxidative stress responses were downregulated between vegetative stages. When we examined the expression of a subset of ten genes associated with plant defense and stress response, the application of thiamethoxam was found to interact with drought stress by enhancing or repressing expression. In drought stressed plants, thiamethoxam induced (upregulated) expression of a thiamine biosynthetic enzyme (THIZ2) and gibberellin regulated protein (GRP), but repressed (downregulated) the expression of an apetala 2 (GmDREB2A;2), lipoxygenase (LIP), and SAM dependent carboxyl methyltransferase (SAM).
  
  
  CONCLUSIONS
  We found evidence that a thiamethoxam seed treatment alters the expression soybean genes related to plant defense and stress response both in the presence and absence of drought stress. Consistent with the thiamethoxam stress shield concept, several genes associated with phytohormones showed enhanced expression in drought stressed plants.
authors.affiliation: Department of Entomology, University of Nebraska, 103 Entomology Hall, Lincoln, NE 68583, USA. mitchell.stamm@basf.com.
authors.forename: Mitchell D
authors.initials: MD
authors.lastname: Stamm
authors.forename: Laramy S
authors.initials: LS
authors.lastname: Enders
authors.forename: Teresa J
authors.initials: TJ
authors.lastname: Donze-Reiner
authors.forename: Frederick P
authors.initials: FP
authors.lastname: Baxendale
authors.forename: Blair D
authors.initials: BD
authors.lastname: Siegfried
authors.forename: Tiffany M
authors.initials: TM
authors.lastname: Heng-Moss
mesh_terms: D018533:Biomass; D019295:Computational Biology / Q000379:methods; D055864:Droughts; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant / Q000187:drug effects*; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000494:pharmacology*; D010078:Oxazines / Q000494:pharmacology*; D015203:Reproducibility of Results; D012639:Seeds / Q000187:drug effects* / Q000235:genetics* / Q000378:metabolism; D013025:Glycine max / Q000187:drug effects* / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics*; D000077922:Thiamethoxam; D013844:Thiazoles / Q000494:pharmacology*; D014158:Transcription, Genetic
chemical_list: D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D013844:Thiazoles; D000077922:Thiamethoxam