Activation of the heat shock response in plants by chlorophenols: transgenic Physcomitrella patens as a sensitive biosensor for organic pollutants

Abstract

The ability to detect early molecular responses to various chemicals is central to the understanding of biological impact of pollutants in a context of varying environmental cues. To monitor stress responses in a model plant, we used transgenic moss Physcomitrella patens expressing the b-glucuronidase reporter (GUS) under the control of the stress-inducible promoter hsp17.3B. Following exposure to pollutants from the dye and paper industry, GUS activity was measured by monitoring a fluorescent product.Chlorophenols, heavy metals and sulphonated anthraquinones were found to specifically activate the hsp17.3B promoter (within hours) in correlation with long-term toxicity effects (within days). At mildly elevated physiological temperatures, the chemical activation of this promoter was strongly amplified, which considerably increased the sensitivity of the bioassay. Together with the activation of hsp17.3B promoter, chlorophenols induced endogenous chaperones that transiently protected a recombinant thermolabile luciferase (LUC) from severe heat denaturation. This sensitive bioassay provides an early warning molecular sensor to industrial pollutants under varying environments, in anticipation to long-term toxic effects in plants.Because of the strong cross-talk between abiotic and chemical stresses that we find, this P. patens line is more likely to serve as a direct toxicity bioassay for pollutants combined with environmental cues, than as an indicator of absolute toxicity thresholds for various pollutants. It is also a powerful tool to study the role of heat shock proteins (HSPs) in plants exposed to combined chemical and environmental stresses.

Plasma Membrane Cyclic Nucleotide Gated Calcium Channels Control Land Plant Thermal Sensing and Acquired Thermotolerance

“…In animals too, the activities of Hsp chaperones (e.g., Hsp70 and sHsps), can block PCD by inhibiting caspase activation and IkB activity (Beere, 2004;Weiss et al, 2007). It is not unlikely that as in animal cells, the upregulation of specific Hsp chaperones in plant cells in response to heat priming, hormones, or drugs (Saidi et al, 2007;Finka et al, 2011), could inhibit the signaling for heat-induced PCD. Overall, such a mechanism would increase chances of plant survival from noxious heat stress.…”

“…Hence, priming pretreatment at 34°C led to a significant thermotolerance in the CNGCb mutant compared with the wild type (see Supplemental Figure 5A online). This was Induced accumulation of the reporter GUS enzyme from the recombinant reporter promoter GmHsp17.3 (Saidi et al, 2005(Saidi et al, , 2007(Saidi et al, , 2009 (A) Scheme of the genetic background of the stable reporter moss strains UBI-AEQ DCNGCb (CNGCb) and UBI-AEQ (wild type [WT]). (B) Moss protonemata grown at 25°C were preincubated with coelenterazine and then exposed to 34 or 38°C.…”

“…Hsps sometimes accumulate in various plant tissues under isothermal conditions (Saidi et al, 2005;Finka et al, 2011), for example, in response to phytohormones, such as abscisic acid (Snyman and Cronjé, 2008), pollutants (Saidi et al, 2007), or when exposed to combinations of mild heat and dehydration stresses (Rizhsky et al, 2004). It is tempting to speculate that the thermosensory CNGC2 and CNGC4, either on their own or in combination with more distantly related CNGCs, such as CNGC6 (Gao et al, 2012), form heteromeric Ca 2+ channels that can trigger Hsp expression at constant temperature and, as such, mediate plant resistances to various environmental stresses in addition to thermotolerance.…”

Membrane lipid composition affects plant heat sensing and modulates Ca2+-dependent heat shock response

“…These findings are in line with earlier reports that membrane fluidizers, such as benzyl alcohol, cause a HSR at non-inducing temperatures in plants and bacteria. 11,12,28 Thus, in Escherichia coli 19 and Synechocystis 29 preadaptation to different growth temperatures modulated the subsequent heat-induced expression levels of major classes of HSPs and affected thermotolerance.…”

“…[8][9][10] Yet, the overexpression of HSPs, so called the heat shock response (HSR), can be activated under mild physiological conditions that are unlikely to cause any protein denaturation in the cell. [11][12][13] Although multiple HSR triggering mechanisms may co-exist, 6,14-16 recent evidences in bacteria, algae, plants and mammalian cells point at the understanding how plants sense and respond to heat stress is central to improve crop tolerance and productivity. recent findings in Physcomitrella patens demonstrated that the controlled passage of calcium ions across the plasma membrane regulates the heat shock response (hSr).…”