Symposium II: Adapting to a Dynamic Environment

Abs # 20004: Genetic analysis of High Temperature Acclimation in Arabidopsis

Presenter:	Vierling, Elizabeth , vierling@u.arizona.edu
Authors	Vierling, Elizabeth  (A)   Lee, Ung  (A)   Larkindale, Jane  (A)   Hong, Suk-Whan  (B)   Katiyar-Agarwal, Surekha  (A)   Escobar, Mindy M (A)   Wie, Chris  (A)
Affiliations:	(A): Department of Biochemistry & Molecular Biophysics, University of Arizona, Tucson, AZ 85721, USA (B): Chonnam National University, Gwangju 500-757, Korea

Plants have the ability to acquire thermotolerance rapidly, within hours, to otherwise normally lethal high temperatures. Even plants growing in their natural distribution range may experience high temperatures that would be lethal in the absence of rapid acclimation. Thus, ability to acquire thermotolerance is likely of significance to plants. We are defining genes involved in acquired thermotolerance by isolating loss-of-function thermotolerance mutants in Arabidopsis, screening existing mutants in stress-related pathways for defects in thermotolerance, using reverse genetics to inhibit candidate genes, and identifying genes regulated during acclimation using microarrays. In a loss-of-function screen for acquired thermotolerance of hypocotyl elongation, 7 loci (HOT loci) were identified, three of which are represented by two alleles. The HOT1 locus encodes the molecular chaperone Hsp101, providing direct evidence that this Hsp is required for thermotolerance. The hot1 mutants are normal in the absence of stress, but show defects in thermotolerance of seed germination, hypocotyl elongation, survival of 10-day old plants, chlorophyll accumulation and in vivo luciferase activity, indicating Hsp101 function impacts many plant processes. In contrast, the other six hot mutants only show a subset of these phenotypes. Suppressors of a hot1 mutant allele have been isolated to define further Hsp101 function. Map-based cloning of the other HOT genes is in progress. None maps to positions containing Hsps or heat shock transcription factors, and all express wild type levels of Hsp101 and small Hsps. Assays of existing mutants reveals that 10-day old seedlings of the fatty acid desaturase mutants fad2,fad7/8, the glutathione S-transferase mutant cad1, a uvh sensitive mutant uvh6, the ABA insensitive mutants abi1, abi2, and abi3, a respiratory burst oxidase mutant, and plants transgenic for nahG all fail to acquire thermotolerance in response to a conditioning pretreatment. Of these, only uvh6 shows a phenotype at the hypocotyl stage that could have been detected in our mutant screen. The growth-stage specificity of the mutant phenotypes may indicate differences in damage incurred during different growth stages. Inhibition of small Hsp expression by RNAi supports a role for the class II sHsps in tolerance to high temperatures. Preliminary microarray analysis of RNA from pretreated plants shows 141 genes that are up-regulated 2 to 13-fold, of which 24 are Hsp genes.