Subset of heat-shock transcription factors required for the early response of Arabidopsis to excess light

Abstract

Sunlight provides energy for photosynthesis and is essential for nearly all life on earth. However, too much or too little light or rapidly fluctuating light conditions cause stress to plants. Rapid changes in the amount of light are perceived as a change in the reduced/oxidized (redox) state of photosynthetic electron transport components in chloroplasts. However, how this generates a signal that is relayed to changes in nuclear gene expression is not well understood. We modified redox state in the reference plant, Arabidopsis thaliana, using either excess light or low light plus the herbicide DBMIB (2,5-dibromo-3-methyl-6-isopropyl-pbenzoquinone), a well-known inhibitor of photosynthetic electron transport. Modification of redox state caused a change in expression of a common set of about 750 genes, many of which are known stress-responsive genes. Among the most highly enriched promoter elements in the induced gene set were heat-shock elements (HSEs), known motifs that change gene expression in response to high temperature in many systems. We show that HSEs from the promoter of the ASCORBATE PEROXIDASE 2 (APX2) gene were necessary and sufficient for APX2 expression in conditions of excess light, or under low light plus the herbicide. We tested APX2 expression phenotypes in overexpression and loss-of-function mutants of 15 Arabidopsis A-type heat-shock transcription factors (HSFs), and identified HSFA1D, HSFA2, and HSFA3 as key factors regulating APX2 expression in diverse stress conditions. Excess light regulates both the subcellular location of HSFA1D and its biochemical properties, making it a key early component of the excess light stress network of plants.

Uncoupling High Light Responses from Singlet Oxygen Retrograde Signaling and Spatial-Temporal Systemic Acquired Acclimation

“…In contrast, the evidence that APX2 may not be induced under HL-alone (Jung et al, 2013) The uncoupled ZAT10 and RRTF1 SAA responses in the dark-light shifted flu background suggest that different retrograde signals can initiate SAA and relay a particular signal to distal tissues, indicating that 1 O 2 -induced SAA is associated with downstream acclimation signaling. Distal marker gene induction in flu appeared to result in both 1 O 2 and H 2 O 2 responses, as NodL and FER1 ROS-responsive markers were in some cases induced more than in treated tissue (Fig.…”

Regulation of Sucrose Transporters and Phloem Loading in Response to Environmental Cues

“…3A). This is likely due to the general detrimental effect on cell function of this condition (Jung et al, 2013). Like different light levels, exposure to increased (480-780 mg mL 21 ) or decreased (50-100 mg mL 21 ) atmospheric CO 2 concentrations compared to ambient levels of 350 to 400 mg mL 21 did not significantly alter the Figure 1.…”

The ROS Wheel: Refining ROS Transcriptional Footprints

“…Transcriptional changes caused by chemical (e.g. inhibitors of mitochondrial and chloroplastic electron transfer chains; Clifton et al, 2005;Jung et al, 2013) and genetic (Vanderauwera et al, 2005;Sewelam et al, 2014) perturbations in ROS-scavenging enzymes, and adverse environmental conditions triggering ROS production such as high light stress (Oelze et al, 2012;Jung et al, 2013), were monitored in dose-and timedependent manners, mainly with the Affymetrix GeneChip Arabidopsis ATH1 Genome Array, which monitors levels of more than 20,000 transcripts simultaneously (Redman et al, 2004). In these experiments, the transcriptomes were found to be extensively reshaped.…”