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A membrane-tethered transcription factor defines a branch of the heat stress response in Arabidopsis thaliana.

ABSTRACT: In plants, heat stress responses are controlled by heat stress transcription factors that are conserved among all eukaryotes and can be constitutively expressed or induced by heat. Heat-inducible transcription factors that are distinct from the "classical" heat stress transcription factors have also been reported to contribute to heat tolerance. Here, we show that bZIP28, a gene encoding a putative membrane-tethered transcription factor, is up-regulated in response to heat and that a bZIP28 null mutant has a striking heat-sensitive phenotype. The heat-inducible expression of genes that encode BiP2, an endoplasmic reticulum (ER) chaperone, and HSP26.5-P, a small heat shock protein, is attenuated in the bZIP28 null mutant. An estradiol-inducible bZIP28 transgene induces a variety of heat and ER stress-inducible genes. Moreover, heat stress appears to induce the proteolytic release of the predicted transcription factor domain of bZIP28 from the ER membrane, thereby causing its redistribution to the nucleus. These findings indicate that bZIP28 is an essential component of a membrane-tethered transcription factor-based signaling pathway that contributes to heat tolerance.

SUBMITTER: Gao H

PROVIDER: S-EPMC2571009 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundHeat stress is a major abiotic stress affecting the growth and development of plants, including crop species. Plants have evolved various adaptive strategies to help them survive heat stress, including maintaining membrane stability, encoding heat shock proteins (HSPs) and ROS-scavenging enzymes, and inducing molecular chaperone signaling. Brassinosteroids (BRs) are phytohormones that regulate various aspects of plant development, which have been implicated also in plant responses to heat stress, and resistance to heat in Arabidopsis thaliana is enhanced by adding exogenous BR. Brassinazole resistant 1 (BZR1), a transcription factor and positive regulator of BR signal, controls plant growth and development by directly regulating downstream target genes. However, the molecular mechanism at the basis of BR-mediated heat stress response is poorly understood. Here, we report the identification of a new factor critical for BR-regulated heat stress tolerance.ResultsWe identified ERF49 in a genetic screen for proteins required for BR-regulated gene expression. We found that ERF49 is the direct target gene of BZR1 and that overexpressing ERF49 enhanced sensitivity of transgenic plants to heat stress. The transcription levels of heat shock factor HSFA2, heat stress-inducible gene DREB2A, and three heat shock protein (HSP) were significantly reduced under heat stress in ERF49-overexpressed transgenic plants. Transcriptional activity analysis in protoplast revealed that BZR1 inhibits ERF49 expression by binding to the promoter of ERF49. Our genetic analysis showed that dominant gain-of-function brassinazole resistant 1-1D mutant (bzr1-1D) exhibited lower sensitivity to heat stress compared with wild-type. Expressing ERF49-SRDX (a dominant repressor reporter of ERF49) in bzr1-1D significantly decreased the sensitivity of ERF49-SRDX/bzr1-1D transgenic plants to heat stress compared to bzr1-1D.ConclusionsOur data provide clear evidence that BR increases thermotolerance of plants by repressing the expression of ERF49 through BZR1, and this process is dependent on the expression of downstream heat stress-inducible genes. Taken together, our work reveals a novel molecular mechanism mediating plant response to high temperature stress.

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A membrane-tethered transcription factor defines a branch of the heat stress response in Arabidopsis thaliana.

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