Cell survival after UV radiation stress in the unicellular chlorophyte Dunaliella tertiolecta is mediated by DNA repair and MAPK phosphorylation

Abstract

Ultraviolet radiation (UVR) induces damage in a variety of organisms, and cells may adapt by developing repair or tolerance mechanisms to counteract such damage; otherwise, the cellular fate is cell death. Here, the effect of UVR-induced cell damage and the associated signalling and repair mechanisms by which cells are able to survive was studied in Dunaliella tertiolecta. UVR did not cause cell death, as shown by the absence of SYTOX Green-positive labelling cells. Ultrastructure analysis by transmission electron microscopy demonstrated that the cells were alive but were subjected to morphological changes such as starch accumulation, chromatin disaggregation, and chloroplast degradation. This behaviour paralleled a decrease in F v/F m and the formation of cyclobutane–pyrimidine dimers, showing a 10-fold increase at the end of the time course. There was a high accumulation of the repressor of transcriptional gene silencing (ROS1), as well as the cell proliferation nuclear antigen (PCNA) in UVR-treated cells, revealing activation of DNA repair mechanisms. The degree of phosphorylation of c-Jun N-terminal kinase (JNK) and p38-like mitogen-activated protein kinases was higher in UVR-exposed cells; however, the opposite occurred with the phosphorylated extracellular signal-regulated kinase (ERK). This confirmed that both JNK and p38 need to be phosphorylated to trigger the stress response, as well as the fact that cell division is arrested when an ERK is dephosphorylated. In parallel, both DEVDase and WEHDase caspase-like enzymatic activities were active even though the cells were not dead, suggesting that these proteases must be considered within a wider frame of stress proteins, rather than specifically being involved in cell death in these organisms.

Effect of CO2, nutrients and light on coastal plankton. IV. Physiological responses

“…DNA damage was assessed in samples collected on Days 0, 4 and 6 by using a modification of the protocol from Boelen et al (1999) as described in García-Gómez et al (2012). For this purpose, samples (1 to 2 l) were collected from each microcosm and gently filtered through 0.8 µm polycarbonate filters.…”

“…Excessive solar radiation can be indicated by in creased membrane permeability, changes in cell elemental composition and decreased growth, among others (Buma et al 1996, Gieskes & Buma 1997, Sobrino et al 2004. Cell photodamage can be minimised by the protective or repairing activity of cell enzymes, including superoxide dismutase, ascorbate peroxidase and catalase involved in scavenging reactive oxygen species (ROS), and lyases, polymerases or ligases involved in DNA repair (Rijstenbil 2002, García-Gómez et al 2012, Bouchard et al 2013. Cellular repair processes depend on ATP supply, and on nitrogen and phosphorus for protein re-synthesis; as a consequence, final response showing the balance between damage and cellular repair may depend on nutrient availability (Litchman et al 2002).…”

Phosphorylation of MAPK-like proteins in three intertidal macroalgae under stress conditions

“…Despite the fact that the study of signal transduction in algae is very recent, different studies with both macro-and microalgae (Jiménez et al 2004, 2007, García-Gómez et al 2012 have clearly shown the presence of p38-like, JNK-like and ERK-like components in algae, as well as their crucial role in acclimation to stress and in cell division (Jiménez et al 2004, 2007, Parages 2012. A procedure has been developed to detect the presence of these MAPK homologues in several species of Chlorophyta, Rhodophyta and Phaeophyta , revealing that phosphory lation of p38-and JNK-like MAPKs occurs in Arctic kelps in response to increasing UVR exposure and temperature (Parages et al 2013) as well as in intertidal macroalgae at the onset of emersion and during periods of the highest irradiation (Parages et al 2014).…”

Metabolic responses and β-carotene production by the unicellular green alga Dunaliella salina exposed to leaf extracts

“…Such increase in fresh weight along with a decrease in cell number was also observed in menadione-treated D. viridis cells (Haghjou et al 2014). Increase in fresh weight caused by starch accumulation was reported in D. tertiolecta illuminated with a combination of photosynthetically active radiation, UVA and UVB despite the lower cell growth (García-Gomez et al 2012). Leaf extracts-induced fresh weight increase can indicate that the remaining alive cells develop an extensive resistance to growth inhibitors.…”

“…Massive accumulation of measured metabolites in this study including β-carotene, Chl, total sugars, and protein content may contribute to increased fresh weight induced by leaf extracts. In addition to starch (Tian & Yu 2009;García-Gomez et al 2012), accumulation of lipids (Yilancioglu et al 2014) induced by oxidative stress in Dunaliella sp. may also be involved.…”