A key general stress response motif is regulated non‐uniformly by CAMTA transcription factors

Abstract

Plants cope with environmental challenges by rapidly triggering and synchronizing mechanisms governing stress-specific and general stress response (GSR) networks. The GSR acts rapidly and transiently in response to various stresses, but the underpinning mechanisms have remained elusive. To define GSR regulatory components we have exploited the Rapid Stress Response Element (RSRE), a previously established functional GSR motif, using Arabidopsis plants expressing a 4xRSRE::Luciferase (RSRE::LUC) reporter. Initially, we searched public microarray datasets and found an enrichment of RSRE in promoter sequences of stress genes. Next, we treated RSRE::LUC plants with wounding and a range of rapidly stress-inducible hormones and detected a robust LUC activity solely in response to wounding. Application of two Ca2+ burst inducers, flagellin22 (flg22) and oligogalacturonic acid, activated RSRE strongly and systemically, while the Ca2+ chelator EGTA significantly reduced wound induction of RSRE::LUC. In line with the signaling function of Ca2+ in transduction events leading to activation of RSRE, we examined role of CALMODULIN-BINDING TRANSCRIPTIONAL ACTIVATORs (CAMTAs) in RSRE induction. Transient expression assays displayed CAMTA3 induction of RSRE and not that of the mutated element mRSRE. Treatment of selected camta mutant lines integrated into RSRE::LUC parent plant, with wounding, flg22, and freezing, established a differential function of these CAMTAs in potentiating the activity of RSRE. Wound response studies using camta double mutants revealed cooperative function of CAMTAs2 and 4 with CAMTA 3 in the RSRE regulation. These studies provide insight into governing components of transduction events and reveal transcriptional modules that tune expression of a key GSR motif.

Determinants of nucleosome positioning and their influence on plant gene expression

“…4C). In addition, many cis-regulatory elements are known to be responsible for dynamic changes of gene expression in various environments (Marcotte et al 1989;Mundy et al 1990;Baker et al 1994;Zou et al 2011;Hickman et al 2013;Benn et al 2014;Franco-Zorrilla et al 2014;Sullivan et al 2014). This raises the question of whether environmental stimuli may affect nucleosome occupancy on cis-regulatory elements and ultimately transcriptional response to environmental perturbation.…”

Distinct Roles for Mitogen-Activated Protein Kinase Signaling and CALMODULIN-BINDING TRANSCRIPTIONAL ACTIVATOR3 in Regulating the Peak Time and Amplitude of the Plant General Stress Response

“…Map-based cloning placed the RAR71 causative mutation near the top of chromosome 2, between markers C2-2 (3.52 Mb) and C2-3 (6.4 Mb;Jander et al, 2002). The presence of CAMTA3, a known activator of RSRE activity (Benn et al, 2014), within this region prompted us to sequence this gene in the RAR71 background, revealing a single C-to-T transition resulting in a premature stop codon in CAMTA3 (Fig. 1C).…”

“…Wound-induced 4xRSRE:LUC activity is rapid (5 min) and transient (reaching a peak at 90-120 min and returning to basal levels within 6-8 h), coinciding with the wound-induced transcriptional pattern of GSR genes with RSRE in their promoter (Walley et al, 2007;Walley and Dehesh, 2010). Furthermore, analysis of genes that are induced following a wide array of stresses, including microbe-associated molecular pattern (MAMP) recognition, osmotic stress, and UV-B light, revealed strong RSRE overrepresentation in early stressresponsive genes, lending strong support to the general, rapid, and transient nature of RSRE-associated gene transcription (Walley et al, 2007;Zou et al, 2011;Benn et al, 2014). 4xRSRE:LUC plants, as a proven genetic tool, provide a platform to dissect the upstream transduction events regulating the GSR.…”

“…This family has been shown to bind to an RSRE-like DNA sequence in vitro (Yang and Poovaiah, 2002). Moreover, recent genetic approaches and transient expression-based assays have shown that CAMTA transcription factors are required for robust 4xRSRE:LUC activity, with CAMTA3 playing the predominant role of the examined family members (CAMTA1-CAMTA4; Benn et al, 2014). However, the specific nature of RSRE transcriptional regulation by CAMTAs has remained an enigma; these transcription factors are constitutively transcribed and present in the nucleus, but strong RSRE-driven gene transcription is observed only in response to stress.…”

“…Among known regulators of the RSRE are the CALMODULIN-BINDING TRANSCRIPTIONAL ACTI-VATOR (CAMTA) family of transcription factors (Bouché et al, 2002;Yang and Poovaiah, 2002;Benn et al, 2014). This family has been shown to bind to an RSRE-like DNA sequence in vitro (Yang and Poovaiah, 2002).…”