Arabidopsis contains four HSFA1 heat shock transcription factors ( HSFA1a , HSFA1b , HSFA1d , and HSFA1e ) that regulate the primary response to high temperature stress responses. These genes have overlapping functions and, while double and triple HSFA1 mutants have thermotolerance phenotypes, these genes have no reported single mutant thermotolerance phenotypes. We used an automated fluorescence microscopy system to quantitate the expression of a HSP17. 6:GFP reporter with high temporal resolution to show that HSFA1d is required for normal heat-induced HSP17.6 expression. HSP17.6 expression is reduced and delayed in hsfa1d-1 mutants. This finding highlights the power of using gene expression kinetics as a quantitative phenotype for discovering the function of genes that exhibit functional redundancy.
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