Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo, 113-8657, Japan.
Mol Genet Genomics. 2011 Dec;286(5-6):321-32. doi: 10.1007/s00438-011-0647-7. Epub 2011 Sep 20.
Arabidopsis DREB2A is a key transcription factor of heat- and drought-responsive gene expression, and DREB2A expression is induced by these stresses. We analyzed the DREB2A promoter and found a heat shock element that functions as a cis-acting element in the heat shock (HS)-responsive expression of DREB2A. Among the 21 Arabidopsis heat shock factors, we chose 4 HsfA1-type proteins as candidate transcriptional activators (HsfA1a, HsfA1b, HsfA1d, and HsfA1e) based on transactivation activity and expression patterns. We generated multiple mutants and found that the HS-responsive expression of DREB2A disappeared in hsfa1a/b/d triple and hsfa1a/b/d/e quadruple mutants. Moreover, HS-responsive gene expression, including that of molecular chaperones and transcription factors, was globally and drastically impaired in the hsfa1a/b/d triple mutant, which exhibited greatly reduced tolerance to HS stress. HsfA1 protein accumulation in the nucleus was negatively regulated by their interactions with HSP90, and other factors potentially strongly activate the HsfA1 proteins under HS stress. The hsfa1a/b/d/e quadruple mutant showed severe growth retardation, and many genes were downregulated in this mutant even under non-stress conditions. Our study indicates that HsfA1a, HsfA1b, and HsfA1d function as main positive regulators in HS-responsive gene expression and four HsfA1-type proteins are important in gene expression for normal plant growth.
拟南芥 DREB2A 是热激和干旱响应基因表达的关键转录因子，DREB2A 的表达受这些胁迫诱导。我们分析了 DREB2A 启动子，发现了一个热休克元件，它作为顺式作用元件在 DREB2A 的热激响应表达中起作用。在 21 种拟南芥热休克因子中，我们根据转录激活活性和表达模式选择了 4 种 HsfA1 型蛋白作为候选转录激活因子（HsfA1a、HsfA1b、HsfA1d 和 HsfA1e）。我们生成了多个突变体，发现 DREB2A 的热激响应表达在 hsfa1a/b/d 三重和 hsfa1a/b/d/e 四重突变体中消失。此外，包括分子伴侣和转录因子在内的热激响应基因表达在 hsfa1a/b/d 三重突变体中被全局严重削弱，该突变体对热激胁迫的耐受性大大降低。HsfA1 蛋白在核内的积累受到它们与 HSP90 相互作用的负调控，其他因素在热激胁迫下可能强烈激活 HsfA1 蛋白。hsfa1a/b/d/e 四重突变体表现出严重的生长迟缓，即使在非胁迫条件下，该突变体中的许多基因也下调。我们的研究表明，HsfA1a、HsfA1b 和 HsfA1d 作为热激响应基因表达的主要正调控因子发挥作用，四种 HsfA1 型蛋白在正常植物生长的基因表达中很重要。
