Edinburgh, Scotland, United Kingdom - TAIR

Low oxygen stress: What is more important
cell identity or survival?
Arabidopsis thaliana was used to elucidate responses to low oxygen (hypoxia)
stress from the organ to cell-type specific level. We used transgenics expressing
a FLAG epitope-tagged ribosomal protein (RPL18B) to immunopurify ribosomeassociated
mRNAs from crude cell extracts of cryo-preserved samples. First, a
35S:FLAG-RPL18 line was used to obtain total and polysomal mRNA
populations from seedlings to evaluate the dynamic response to 2h or 9h of
hypoxia as well as re-oxygenation (9h hypoxia + 1h air). The changes in
translated mRNAs and metabolites exposed a rapid and reversible
reconfiguration of carbon and nitrogen metabolism that augments anaerobic ATP
production. A major energy conserving mechanism was the inhibition of
translation of over 60% of the cellular mRNAs. This sequestration was rapidly
reversible, with 90% recovery of polysomes within 10 min of reoxygenation.
Remarkably, some strongly induced transcripts were only recruited to polysomes
upon reoxygenation. Second, to identify organ and cell-specific distinctions in
response to hypoxia, 13 promoters with regional or cell-type specific expression
were used to drive FLAG-RPL18B. This collection of lines permitted the
comparative profiling of cell-specific mRNA populations in the seedling root apex,
whole root and shoot. For each promoter:FLAG-RPL18B line, ribosomeassociated
mRNAs were evaluated under control conditions and after 2 h of
hypoxia, producing a highly informative dataset for >17,000 genes. Transcription
factor mRNAs provided a complex fingerprint for individual cell types under
control conditions. The transcription factor mRNA population in ribosome
complexes was generally perturbed by hypoxia, indicating that the stress largely
overrides cell-specific patterns of protein production. We found that all organs
and cell types invoked a core response to hypoxia, including increased
translation of ~50 mRNAs, of which half are proteins of unknown function.
Specific responses to hypoxia in the root, shoot and individual cell-types were
resolved that provide new insight into the intricacies of the response to low
oxygen stress. (Funding: NSF 2010 IBN-0420152 and IGERT DGE 0504249).
34
L09
Thursday 10:00 - 10:30
Environmental Responses
Julia Bailey-Serres
Department of Botany and
Plant Sciences
University of California
Riverside
CA 92521
USA