Phosphoprotein SAK1 is a regulator of acclimation to singlet oxygen in Chlamydomonas reinhardtii

Wakao, Setsuko; Chin, Brian; Ledford, Heidi; Dent, Rachel M.; Casero, David; Pellegrini, Matteo; Merchant, Sabeeha; Niyogi, Krishna

doi:10.7554/elife.02286

Cited by 45 publications

(80 citation statements)

References 80 publications

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“…DCMU treatment is known to result in 1 O 2 production (Fufezan et al ., ), and as the RB treatment shows, 1 O 2 is capable of inducing VTC2 expression and Asc accumulation (Fig. b; see also Wakao et al ., ).…”

Section: Resultsmentioning

confidence: 97%

Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress‐induced response via the VTC2 gene encoding GDP‐l‐galactose phosphorylase

et al. 2017

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Ascorbate (vitamin C) plays essential roles in stress resistance, development, signaling, hormone biosynthesis and regulation of gene expression; however, little is known about its biosynthesis in algae. In order to provide experimental proof for the operation of the Smirnoff-Wheeler pathway described for higher plants and to gain more information on the regulation of ascorbate biosynthesis in Chlamydomonas reinhardtii, we targeted the VTC2 gene encoding GDP-l-galactose phosphorylase using artificial microRNAs. Ascorbate concentrations in VTC2 amiRNA lines were reduced to 10% showing that GDP-l-galactose phosphorylase plays a pivotal role in ascorbate biosynthesis. The VTC2 amiRNA lines also grow more slowly, have lower chlorophyll content, and are more susceptible to stress than the control strains. We also demonstrate that: expression of the VTC2 gene is rapidly induced by H O and O resulting in a manifold increase in ascorbate content; in contrast to plants, there is no circadian regulation of ascorbate biosynthesis; photosynthesis is not required per se for ascorbate biosynthesis; and Chlamydomonas VTC2 lacks negative feedback regulation by ascorbate in the physiological concentration range. Our work demonstrates that ascorbate biosynthesis is also highly regulated in Chlamydomonas albeit via mechanisms distinct from those previously described in land plants.

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Section: Resultsmentioning

confidence: 97%

Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress‐induced response via the VTC2 gene encoding GDP‐l‐galactose phosphorylase

et al. 2017

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“…Reactive electrophile species are not only destructive, but also likely candidates for mediating 1 O 2 signaling (Fischer et al ). Chloroplast to nucleus signaling during 1 O 2 acclimation involves the light‐induced cytosolic protein SAK1, which regulates the expression of many nuclear genes, including gpxh (Wakao et al ). Phosphorylation is also part SAK1 activation (Wakao et al ), showing that acclimation to HL and associated 1 O 2 production is complex.…”

Section: Discussionmentioning

confidence: 99%

“…Chloroplast to nucleus signaling during 1 O 2 acclimation involves the light‐induced cytosolic protein SAK1, which regulates the expression of many nuclear genes, including gpxh (Wakao et al ). Phosphorylation is also part SAK1 activation (Wakao et al ), showing that acclimation to HL and associated 1 O 2 production is complex. Moreover, a different pathway is more dominant in gst1 expression, which involves RES‐sensitive transcription factors like SOR1 that contain electrophile response elements (Fischer et al ).…”

Section: Discussionmentioning

confidence: 99%

Chlamydomonas reinhardtii responding to high light: a role for 2‐propenal (acrolein)

Roach

Baur

Stöggl

et al. 2017

Physiologia Plantarum

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High light causes photosystem II to generate singlet oxygen ( O ), a reactive oxygen species (ROS) that can react with membrane lipids, releasing reactive electrophile species (RES), such as acrolein. To investigate how RES may contribute to light stress responses, Chlamydomonas reinhardtii was high light-treated in photoautotrophic and mixotrophic conditions and also in an oxygen-enriched atmosphere to elevate ROS production. The responses were compared to exogenous acrolein. Non-photochemical quenching (NPQ) was higher in photoautotrophic cells, as a consequence of a more de-epoxidized state of the xanthophyll cycle pool and more LHCSR3 protein, showing that photosynthesis was under more pressure than in mixotrophic cells. Photoautotrophic cells had lowered α-tocopherol and β-carotene contents and a higher level of protein carbonylation, indicators of elevated O production. Levels of glutathione, glutathione peroxidase (GPX5) and glutathione-S-transferase (GST1), important antioxidants against RES, were also increased in photoautotrophic cells. In parallel to the wild-type, the LHCSR3-deficient npq4 mutant was high light-treated, which in photoautotrophic conditions exhibited particular sensitivity under elevated oxygen, the treatment that induced the highest RES levels, including acrolein. The npq4 mutant had more GPX5 and GST1 alongside higher levels of carbonylated protein and a more oxidized glutathione redox state. In wild-type cells glutathione contents doubled after 4 h treatment, either with high light under elevated oxygen or with a non-critical dose (600 ppm) of acrolein. Exogenous acrolein also increased GST1 levels, but not GPX5. Overall, RES-associated oxidative damage and glutathione metabolism are prominently associated with light stress and potentially in signaling responses of C. reinhardtii.

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“…The set of transcripts whose abundance was considered to be significantly differentially abundant (as described above) between 1 h after addition of 1 mM H 2 O 2 and immediately prior to addition was generated. For comparisons of transcripts with increased abundance in the presence of Ni 2 in the CRR1 strain and increased abundance in previously published RNA-Seq experiments, before determining the overlap we applied the cutoffs of Ն10 FPKM/reads per kilobase per million and a Ն2.0-fold change in expression between mock-treated cultures and cultures to which rose bengal was added (46), 0 h and either 12 h, 31 h, 43 h, or 48 h of ClpP1 depletion (23), 0 h and either 2 h or 8 h after rapamycin addition (23), 0 h and 6 h after transfer to dark anoxic conditions (47), conditions with 20 M Fe supplementation and conditions with either 1 M or 0.25 M Fe supplementation (48), the presence and absence of Cu (49), and the presence and absence of Zn (50). The list of upregulated transcripts (that met these cutoffs) from each data set was then compared to the list of transcripts that increased in abundance (using the same cutoffs) in the CRR1 strain after Ni 2ϩ addition.…”

Section: Methodsmentioning

confidence: 99%

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

et al. 2015

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Autophagy is an intracellular self-degradation pathway by which eukaryotic cells recycle their own material in response to specific stress conditions. Exposure to high concentrations of metals causes cell damage, although the effect of metal stress on autophagy has not been explored in photosynthetic organisms. In this study, we investigated the effect of metal excess on autophagy in the model unicellular green alga Chlamydomonas reinhardtii. We show in cells treated with nickel an upregulation of ATG8 that is independent of CRR1, a global regulator of copper signaling in Chlamydomonas. A similar effect on ATG8 was observed with copper and cobalt but not with cadmium or mercury ions. Transcriptome sequencing data revealed an increase in the abundance of the protein degradation machinery, including that responsible for autophagy, and a substantial overlap of that increased abundance with the hydrogen peroxide response in cells treated with nickel ions. Thus, our results indicate that metal stress triggers autophagy in Chlamydomonas and suggest that excess nickel may cause oxidative damage, which in turn activates degradative pathways, including autophagy, to clear impaired components and recover cellular homeostasis. Eukaryotic cells are able to degrade and recycle their own material when they are exposed to nutrient starvation or other adverse conditions through a catabolic pathway known as macroautophagy or autophagy. This process is characterized by the formation of double-membrane vesicles termed autophagosomes that engulf and deliver cytosolic components to the vacuole/lysosome for degradation (1-4). The primary function of autophagy is to recycle cytoplasmic material as well as to clear damaged organelles or toxic cellular components generated during stress in order to maintain cellular homeostasis. In higher eukaryotes, autophagy has also been implicated in cell differentiation, development and cell death, and several human pathologies, such as cancer and neurodegenerative diseases (5, 6).Autophagy is mediated by highly conserved autophagy-related (ATG) genes, which have been described in organisms ranging from yeasts to mammals. Some ATG proteins are required for the formation of the autophagosome and constitute the core autophagy machinery (4,7,8). This group of proteins includes the ATG8 and ATG12 ubiquitin-like systems required for vesicle expansion. The ATG8 protein has been widely used to monitor autophagy in many systems (9) because, unlike other ATG proteins, this protein firmly binds to the autophagosome membrane through a covalent bond to phosphatidylethanolamine (PE). Most of the core ATG proteins are conserved in land plants (10-12) and in evolutionarily distant algae, including freshwater species, such as the model green alga Chlamydomonas reinhardtii (herein referred to as Chlamydomonas) (13) and marine species (14). Our current knowledge about autophagy in algae is still limited compared to our knowledge about autophagy in other eukaryotes, but recent studies, mainly performed in Chlamydomon...

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Phosphoprotein SAK1 is a regulator of acclimation to singlet oxygen in Chlamydomonas reinhardtii

Cited by 45 publications

References 80 publications

Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress‐induced response via the VTC2 gene encoding GDP‐l‐galactose phosphorylase

Regulation of ascorbate biosynthesis in green algae has evolved to enable rapid stress‐induced response via the VTC2 gene encoding GDP‐l‐galactose phosphorylase

Chlamydomonas reinhardtii responding to high light: a role for 2‐propenal (acrolein)

Activation of Autophagy by Metals in Chlamydomonas reinhardtii

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