Signalisation de l'oxygène singulet et acclimatation des plantes aux contraintes environnementales

En conditions de stress biotiques et abiotiques la production de plusieurs espèces réactives de l’oxygène (ERO) dans différents compartiments spécialisés de la cellule végétale est inévitable. L’oxygène singulet (1O2) a été identifié comme la principale ERO produite dans le chloroplaste au cours d’un stress lumineux. Cette ERO est très réactive et a une durée de vie courte d’environ 3 s dans les tissus biologiques, ce qui amène à penser que l’oxygène singulet agit principalement par cytotoxicité. Cependant, il a été récemment établi que l’oxygène singulet fonctionne aussi comme une molécule signal impliquée dans la signalisation rétrograde chloroplaste-noyau conduisant soit à la mort cellulaire programmée, soit à l’acclimatation. En raison des propriétés particulières de l’oxygène singulet, il est peu probable que cette ERO voyage en dehors du chloroplaste pour induire des changements d’expression de gènes nucléaires. Une possibilité est que l’oxygène singulet agisse via des médiateurs. Nous avons identifié un produit d’oxydation du β-carotène, le dihydroactinidiolide (dhA), comme intermédiaire dans la voie de signalisation de l’oxygène singulet, qui agit d’une manière similaire à un autre produit d’oxydation du β-carotène, le β-cyclocitral, précédemment identifié comme intermédiaire dans la voie de signalisation de l’oxygène singulet. Nous avons aussi mis en évidence le rôle dans la voie de signalisation régulée par le β-cyclocitral de la protéine MBS1 (METHYLENE BLUE SENSITIVITY 1), et montré que la mort cellulaire programmée induite par l’oxygène singulet chez l’Arabidopsis est controllée par une serine-threonine kinase, OXI1 (OXIDATIVE SIGNAL INDUCIBLE 1).During biotic and abiotic stress conditions, the production of several reactive oxygen species (ROS) at different specialized compartments of the cell is inevitable. Singlet oxygen (1O2) was identified to be the predominant ROS produced in the chloroplast during high light stress. This molecule is highly reactive, with a short life time of about 3 µs in biological tissues. Such properties make believe that the predominant effect of 1O2 in plants is cytotoxicity. However, 1O2 has been identified to function as a chloroplast-to-nucleus retrograde signaling molecule, leading to acclimation or programmed cell death (PCD). Cognizant of the properties of 1O2, it is most unlikely to travel directly from the chloroplast to the nucleus to signal changes in nuclear gene expression. One possibility is that 1O2 carries out this signaling function with the help of mediators. We identify a β-carotene oxidation product, dihydroactinidiolide (dhA) as a 1O2 signaling intermediate, which function similarly to the β-carotene oxidation product β-cyclocitral, previously identified to be a mediator of 1O2 plastid-nuclear retrograde signaling in Arabidopsis. We reveal a dependence of the β-cyclocitral-mediated signaling pathway on the MBS1 (METHYLENE BLUE SENSITIVITY 1) protein, and show that Programmed cell death induced by 1O2 is mediated by the serine-threonine kinase, OXI1(OXIDATIVE SIGNAL INDUCIBLE 1)

Dihydroactinidiolide, a high light-induced β-carotene derivative that can regulate gene expression and photoacclimation in <em>Arabidopsis</em>

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Singlet Oxygen-Induced Cell Death in Arabidopsis under High Light Stress is Controlled by OXI1 Kinase

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METHYLENE BLUE SENSITIVITY 1 (MBS1) is required for acclimation of Arabidopsis to singlet oxygen and acts downstream of β‐cyclocitral

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Luminescence imaging of leaf damage induced by lipid peroxidation products and its modulation by β‐cyclocitral

International audienceLipid peroxidation is a primary event associated with oxidative stress in plants. This phenomenon secondarily generates bioactive and/or toxic compounds such as reactive carbonyl species (RCS), phytoprostanes, and phytofurans, as confirmed here in Arabidopsis plants exposed to photo‐oxidative stress conditions. We analyzed the effects of exogenous applications of secondary lipid oxidation products on Arabidopsis plants by luminescence techniques. Oxidative damage to attached leaves was measured by autoluminescence imaging, using a highly sensitive CCD camera, and the activity of the detoxification pathway, dependent on the transcription regulator SCARECROW‐LIKE 14 (SCL14), was monitored with a bioluminescent line expressing the firefly LUCIFERASE (LUC) gene under the control of the ALKENAL REDUCTASE (AER) gene promoter. We identified 4‐hydroxynonenal (HNE), and to a lesser extent 4‐hydroxyhexenal (HHE), as highly reactive compounds that are harmful to leaves and can trigger AER gene expression, contrary to other RCS (pentenal, hexenal) and to isoprostanoids. Although the levels of HNE and other RCS were enhanced in the SCL14‐deficient mutant (scl14), exogenously applied HNE was similarly damaging to this mutant, its wild‐type parent and a SCL14‐overexpressing transgenic line (OE:SCL14). However, strongly boosting the SCL14 detoxification pathway and AER expression by a pre‐treatment of OE:SCL14 with the signaling apocarotenoid β‐cyclocitral canceled the damaging effects of HNE. Conversely, in the scl14 mutant, the effects of β‐cyclocitral and HNE were additive, leading to enhanced leaf damage. These results indicate that the cellular detoxification pathway induced by the low‐toxicity β‐cyclocitral targets highly toxic compounds produced during lipid peroxidation, reminiscent of a safener‐type mode of action