title: Tobacco drought stress responses reveal new targets for Solanaceae crop improvement.
abstract: BACKGROUND
  The Solanaceae are an economically important family of plants that include tobacco (Nicotiana tabacum L.), tomato, and potato. Drought is a major cause of crop losses.
  
  
  RESULTS
  We have identified major changes in physiology, metabolites, mRNA levels, and promoter activities during the tobacco response to drought. We have classified these as potential components of core responses that may be common to many plant species or responses that may be family/species-specific features of the drought stress response in tobacco or the Solanaceae. In tobacco the largest increase in any metabolite was a striking 70-fold increase in 4-hydroxy-2-oxoglutaric acid (KHG) in roots that appears to be tobacco/Solanaceae specific. KHG is poorly characterized in plants but is broken down to pyruvate and glyoxylate after the E. coli SOS response to facilitate the resumption of respiration. A similar process in tobacco would represent a mechanism to restart respiration upon water availability after drought. At the mRNA level, transcription factor gene induction by drought also showed both core and species/family specific responses. Many Group IX Subgroup 3 AP2/ERF transcription factors in tobacco appear to play roles in nicotine biosynthesis as a response to herbivory, whereas their counterparts in legume species appear to play roles in drought responses. We observed apparent Solanaceae-specific drought induction of several Group IId WRKY genes. One of these, NtWRKY69, showed ABA-independent drought stress-inducible promoter activity that moved into the leaf through the vascular tissue and then eventually into the surrounding leaf cells.
  
  
  CONCLUSIONS
  We propose components of a core metabolic response to drought stress in plants and also show that some major responses to drought stress at the metabolome and transcriptome levels are family specific. We therefore propose that the observed family-specific changes in metabolism are regulated, at least in part, by family-specific changes in transcription factor activity. We also present a list of potential targets for the improvement of Solanaceae drought responses.
authors.affiliation: Texas A&M AgriLife Research and Extension Center, Dallas, Texas, 75252, USA. roel.rabara@tamu.edu.
authors.forename: Roel C
authors.initials: RC
authors.lastname: Rabara
authors.affiliation: Molecular and Computational Biology Section, Dana & David Dornsife College of Letters, Arts and Sciences, University of Southern California, Los Angeles, CA, USA. tprateek@dornsife.usc.edu.
authors.forename: Prateek
authors.initials: P
authors.lastname: Tripathi
authors.affiliation: Department of Biology and Microbiology, South Dakota State University, Brookings, SD, 57007, USA. Neil.Reese@sdstate.edu.
authors.forename: R Neil
authors.initials: RN
authors.lastname: Reese
authors.affiliation: Department of Biological Sciences, University of North Texas, Denton, TX, 76203, USA. dlrushton82@gmail.com.
authors.forename: Deena L
authors.initials: DL
authors.lastname: Rushton
authors.affiliation: Metabolon, Inc., 617 Davis Drive, Durham, NC, 277133, USA. DAlexander@metabolon.com.
authors.forename: Danny
authors.initials: D
authors.lastname: Alexander
authors.affiliation: Department of Biology, University of Virginia, Charlottesville, Virginia, 22904, USA. mpt9g@virginia.edu.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Timko
authors.affiliation: School of Life Sciences, University of Nevada, Las Vegas, 89154, USA. jeffery.shen@unlv.edu.
authors.forename: Qingxi J
authors.initials: QJ
authors.lastname: Shen
authors.affiliation: Texas A&M AgriLife Research and Extension Center, Dallas, Texas, 75252, USA. paul.rushton@tamu.edu.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Rushton
mesh_terms: D055864:Droughts; D007656:Ketoglutaric Acids / Q000378:metabolism; D055442:Metabolome; D010802:Phylogeny; D010937:Plant Growth Regulators / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000145:classification / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000254:growth & development / Q000378:metabolism; D025341:Principal Component Analysis; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D013312:Stress, Physiological; D014026:Nicotiana / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D014157:Transcription Factors / Q000145:classification / Q000235:genetics / Q000378:metabolism
chemical_list: D007656:Ketoglutaric Acids; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; D014157:Transcription Factors