title: High-level expression of sugar inducible gene2 (HSI2) is a negative regulator of drought stress tolerance in Arabidopsis.
abstract: BACKGROUND
  HIGH-LEVEL EXPRESSION OF SUGAR INDUCIBLE GENE2 (HSI2), also known as VAL1, is a B3 domain transcriptional repressor that acts redundantly with its closest relative, HSI2-LIKE1 (HSL1), to suppress the seed maturation program following germination. Mutant hsi2 hsl1 seedlings are arrested early in development and differentially express a number of abiotic stress-related genes. To test the potential requirement for HSI2 during abiotic stress, hsi2 single mutants and plants overexpressing HSI2 were subjected to simulated drought stress by withholding watering, and characterized through physiological, metabolic and gene expression studies.
  
  
  RESULTS
  The hsi2 mutants demonstrated reduced wilting and maintained higher relative water content than wild-type after withholding watering, while the overexpressing lines displayed the opposite phenotype. The hsi2 mutant displayed lower constitutive and ABA-induced stomatal conductance than wild-type and accumulated lower levels of ABA metabolites and several osmolytes and osmoprotectants following water withdrawal. Microarray comparisons between wild-type and the hsi2 mutant revealed that steady-state levels of numerous stress-induced genes were up-regulated in the mutant in the absence of stress but down-regulated at visible wilting. Plants with altered levels of HSI2 responded to exogenous application of ABA and a long-lived ABA analog, but the hsi2 mutant did not show altered expression of several ABA-responsive or ABA signalling genes 4 hr after application.
  
  
  CONCLUSIONS
  These results implicate HSI2 as a negative regulator of drought stress response in Arabidopsis, acting, at least in part, by regulating transpirational water loss. Metabolic and global transcript profiling comparisons of the hsi2 mutant and wild-type plants do not support a model whereby the greater drought tolerance observed in the hsi2 mutant is conferred by the accumulation of known osmolytes and osmoprotectants. Instead, data are consistent with mutants experiencing a relatively milder dehydration stress following water withdrawal.
authors.forename: Nirmala
authors.initials: N
authors.lastname: Sharma
authors.forename: Yarnel
authors.initials: Y
authors.lastname: Bender
authors.forename: Kerry
authors.initials: K
authors.lastname: Boyle
authors.affiliation: National Research Council Canada, 110 Gymnasium Place, Saskatoon, SK S7N 0W9, Canada. Pierre.Fobert@nrc-cnrc.gc.ca.
authors.forename: Pierre R
authors.initials: PR
authors.lastname: Fobert
mesh_terms: D000040:Abscisic Acid / Q000494:pharmacology; D000222:Adaptation, Physiological / Q000187:drug effects / Q000235:genetics; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics* / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics; D055864:Droughts; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D063990:Gene Ontology; D007700:Kinetics; D055442:Metabolome / Q000187:drug effects / Q000235:genetics; D058977:Molecular Sequence Annotation; D016254:Mutagenesis, Insertional / Q000187:drug effects / Q000235:genetics; D009154:Mutation / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D054046:Plant Stomata / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D015203:Reproducibility of Results; D013312:Stress, Physiological / Q000187:drug effects / Q000235:genetics; D059467:Transcriptome / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; C504531:HSI2 protein, Arabidopsis; D012333:RNA, Messenger; D012097:Repressor Proteins; C036483:T-DNA; D000040:Abscisic Acid