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1.
Plant J ; 102(6): 1266-1280, 2020 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-31975462

RESUMO

Singlet oxygen (1 O2 ) is a by-product of photosynthesis that triggers a signalling pathway leading to stress acclimation or to cell death. By analyzing gene expressions in a 1 O2 -overproducing Arabidopsis mutant (ch1) under different light regimes, we show here that the 1 O2 signalling pathway involves the endoplasmic reticulum (ER)-mediated unfolded protein response (UPR). ch1 plants in low light exhibited a moderate activation of UPR genes, in particular bZIP60, and low concentrations of the UPR-inducer tunicamycin enhanced tolerance to photooxidative stress, together suggesting a role for UPR in plant acclimation to low 1 O2 levels. Exposure of ch1 to high light stress ultimately leading to cell death resulted in a marked upregulation of the two UPR branches (bZIP60/IRE1 and bZIP28/bZIP17). Accordingly, mutational suppression of bZIP60 and bZIP28 increased plant phototolerance, and a strong UPR activation by high tunicamycin concentrations promoted high light-induced cell death. Conversely, light acclimation of ch1 to 1 O2 stress put a limitation in the high light-induced expression of UPR genes, except for the gene encoding the BIP3 chaperone, which was selectively upregulated. BIP3 deletion enhanced Arabidopsis photosensitivity while plants treated with a chemical chaperone exhibited enhanced phototolerance. In conclusion, 1 O2 induces the ER-mediated UPR response that fulfils a dual role in high light stress: a moderate UPR, with selective induction of BIP3, is part of the acclimatory response to 1 O2 , and a strong activation of the whole UPR is associated with cell death.

2.
iScience ; 19: 461-473, 2019 Sep 27.
Artigo em Inglês | MEDLINE | ID: mdl-31437750

RESUMO

ß-Cyclocitral (ß-CC) is a volatile compound deriving from 1O2 oxidation of ß-carotene in plant leaves. ß-CC elicits a retrograde signal, modulating 1O2-responsive genes and enhancing tolerance to photooxidative stress. Here, we show that ß-CC is converted into water-soluble ß-cyclocitric acid (ß-CCA) in leaves. This metabolite is a signal that enhances plant tolerance to drought by a mechanism different from known responses such as stomatal closure, osmotic potential adjustment, and jasmonate signaling. This action of ß-CCA is a conserved mechanism, being observed in various plant species, and it does not fully overlap with the ß-CC-dependent signaling, indicating that ß-CCA induces only a branch of ß-CC signaling. Overexpressing SCARECROW-LIKE14 (SCL14, a regulator of xenobiotic detoxification) increased drought tolerance and potentiated the protective effect of ß-CCA, showing the involvement of the SCL14-dependent detoxification in the phenomenon. ß-CCA is a bioactive apocarotenoid that could potentially be used to protect crop plants against drought.

3.
Commun Biol ; 2: 220, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31240258

RESUMO

Photosynthesis produces organic carbon via a light-driven electron flow from H2O to CO2 that passes through a pool of plastoquinone molecules. These molecules are either present in the photosynthetic thylakoid membranes, participating in photochemistry (photoactive pool), or stored (non-photoactive pool) in thylakoid-attached lipid droplets, the plastoglobules. The photoactive pool acts also as a signal of photosynthetic activity allowing the adaptation to changes in light condition. Here we show that, in Arabidopsis thaliana, proton gradient regulation 6 (PGR6), a predicted atypical kinase located at plastoglobules, is required for plastoquinone homoeostasis, i.e. to maintain the photoactive plastoquinone pool. In a pgr6 mutant, the photoactive pool is depleted and becomes limiting under high light, affecting short-term acclimation and photosynthetic efficiency. In the long term, pgr6 seedlings fail to adapt to high light and develop a conditional variegated leaf phenotype. Therefore, PGR6 activity, by regulating plastoquinone homoeostasis, is required to cope with high light.


Assuntos
Homeostase/fisiologia , Fotossíntese/fisiologia , Plastoquinona/metabolismo , Adaptação Biológica/fisiologia , Arabidopsis , Luz , Folhas de Planta/crescimento & desenvolvimento , Folhas de Planta/metabolismo , Plantas Geneticamente Modificadas , Plântula/crescimento & desenvolvimento , Plântula/metabolismo
4.
Plant Physiol ; 180(3): 1691-1708, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31123095

RESUMO

Singlet oxygen produced from triplet excited chlorophylls in photosynthesis is a signal molecule that can induce programmed cell death (PCD) through the action of the OXIDATIVE STRESS INDUCIBLE 1 (OXI1) kinase. Here, we identify two negative regulators of light-induced PCD that modulate OXI1 expression: DAD1 and DAD2, homologs of the human antiapoptotic protein DEFENDER AGAINST CELL DEATH. Overexpressing OXI1 in Arabidopsis (Arabidopsis thaliana) increased plant sensitivity to high light and induced early senescence of mature leaves. Both phenomena rely on a marked accumulation of jasmonate and salicylate. DAD1 or DAD2 overexpression decreased OXI1 expression, jasmonate levels, and sensitivity to photooxidative stress. Knock-out mutants of DAD1 or DAD2 exhibited the opposite responses. Exogenous applications of jasmonate upregulated salicylate biosynthesis genes and caused leaf damage in wild-type plants but not in the salicylate biosynthesis mutant Salicylic acid induction-deficient2, indicating that salicylate plays a crucial role in PCD downstream of jasmonate. Treating plants with salicylate upregulated the DAD genes and downregulated OXI1 We conclude that OXI1 and DAD are antagonistic regulators of cell death through modulating jasmonate and salicylate levels. High light-induced PCD thus results from a tight control of the relative activities of these regulating proteins, with DAD exerting a negative feedback control on OXI1 expression.

5.
New Phytol ; 223(4): 1776-1783, 2019 09.
Artigo em Inglês | MEDLINE | ID: mdl-31090944

RESUMO

Stressful environmental conditions lead to the production of reactive oxygen species in the chloroplasts, due to limited photosynthesis and enhanced excitation pressure on the photosystems. Among these reactive species, singlet oxygen (1 O2 ), which is generated at the level of the PSII reaction center, is very reactive, readily oxidizing macromolecules in its immediate surroundings, and it has been identified as the principal cause of photooxidative damage in plant leaves. The two ß-carotene molecules present in the PSII reaction center are prime targets of 1 O2 oxidation, leading to the formation of various oxidized derivatives. Plants have evolved sensing mechanisms for those PSII-generated metabolites, which regulate gene expression, putting in place defense mechanisms and alleviating the effects of PSII-damaging conditions. A new picture is thus emerging which places PSII as a sensor and transducer in plant stress resilience through its capacity to generate signaling metabolites under excess light energy. This review summarizes new advances in the characterization of the apocarotenoids involved in the PSII-mediated stress response and of the pathways elicited by these molecules, among which is the xenobiotic detoxification.


Assuntos
Adaptação Fisiológica , Complexo de Proteína do Fotossistema II/metabolismo , Estresse Fisiológico , beta Caroteno/metabolismo , Oxirredução , Fotossíntese , beta Caroteno/química
6.
Commun Biol ; 2: 159, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31069268

RESUMO

In the last common enzymatic step of tetrapyrrole biosynthesis, prior to the branching point leading to the biosynthesis of heme and chlorophyll, protoporphyrinogen IX (Protogen) is oxidised to protoporphyrin IX (Proto) by protoporphyrinogen IX oxidase (PPX). The absence of thylakoid-localised plastid terminal oxidase 2 (PTOX2) and cytochrome b 6 f complex in the ptox2 petB mutant, results in almost complete reduction of the plastoquinone pool (PQ pool) in light. Here we show that the lack of oxidised PQ impairs PPX function, leading to accumulation and subsequently uncontrolled oxidation of Protogen to non-metabolised Proto. Addition of 3(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) prevents the over-reduction of the PQ pool in ptox2 petB and decreases Proto accumulation. This observation strongly indicates the need of oxidised PQ as the electron acceptor for the PPX reaction in Chlamydomonas reinhardtii. The PPX-PQ pool interaction is proposed to function as a feedback loop between photosynthetic electron transport and chlorophyll biosynthesis.


Assuntos
Proteínas de Algas/genética , Chlamydomonas reinhardtii/enzimologia , Clorofila/biossíntese , Regulação da Expressão Gênica de Plantas , Plastoquinona/metabolismo , Protoporfirinogênio Oxidase/genética , Proteínas de Algas/metabolismo , Chlamydomonas reinhardtii/efeitos dos fármacos , Chlamydomonas reinhardtii/genética , Complexo Citocromos b6f/genética , Complexo Citocromos b6f/metabolismo , Diurona/farmacologia , Transporte de Elétrons , Retroalimentação Fisiológica , Herbicidas/farmacologia , Oxirredução , Fotossíntese/efeitos dos fármacos , Fotossíntese/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Plastídeos/efeitos dos fármacos , Plastídeos/enzimologia , Plastídeos/genética , Protoporfirinogênio Oxidase/metabolismo , Protoporfirinas/metabolismo
7.
J Exp Bot ; 70(6): 1875-1889, 2019 03 27.
Artigo em Inglês | MEDLINE | ID: mdl-30785184

RESUMO

Numerous proteins require a metallic co-factor for their function. In plastids, the maturation of iron-sulfur (Fe-S) proteins necessitates a complex assembly machinery. In this study, we focused on Arabidopsis thaliana NFU1, NFU2, and NFU3, which participate in the final steps of the maturation process. According to the strong photosynthetic defects observed in high chlorophyll fluorescence 101 (hcf101), nfu2, and nfu3 plants, we determined that NFU2 and NFU3, but not NFU1, act immediately upstream of HCF101 for the maturation of [Fe4S4]-containing photosystem I subunits. An additional function of NFU2 in the maturation of the [Fe2S2] cluster of a dihydroxyacid dehydratase was obvious from the accumulation of precursors of the branched-chain amino acid synthesis pathway in roots of nfu2 plants and from the rescue of the primary root growth defect by supplying branched-chain amino acids. The absence of NFU3 in roots precluded any compensation. Overall, unlike their eukaryotic and prokaryotic counterparts, which are specific to [Fe4S4] proteins, NFU2 and NFU3 contribute to the maturation of both [Fe2S2] and [Fe4S4] proteins, either as a relay in conjunction with other proteins such as HCF101 or by directly delivering Fe-S clusters to client proteins. Considering the low number of Fe-S cluster transfer proteins relative to final acceptors, additional targets probably await identification.

8.
Plant Cell ; 30(10): 2495-2511, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-30262551

RESUMO

When exposed to unfavorable environmental conditions, plants can absorb light energy in excess of their photosynthetic capacities, with the surplus energy leading to the production of reactive oxygen species and photooxidative stress. Subsequent lipid peroxidation generates toxic reactive carbonyl species whose accumulation culminates in cell death. ß-Cyclocitral, an oxidized by-product of ß-carotene generated in the chloroplasts, mediates a protective retrograde response that lowers the levels of toxic peroxides and carbonyls, limiting damage to intracellular components. In this study, we elucidate the molecular mechanism induced by ß-cyclocitral in Arabidopsis thaliana and show that the xenobiotic detoxification response is involved in the tolerance to excess light energy. The involvement of the xenobiotic response suggests a possible origin for this pathway. Furthermore, we establish the hierarchical structure of this pathway that is mediated by the ß-cyclocitral-inducible GRAS protein SCARECROW LIKE14 (SCL14) and involves ANAC102 as a pivotal component upstream of other ANAC transcription factors and of many enzymes of the xenobiotic detoxification response. Finally, the SCL14-dependent protective mechanism is also involved in the low sensitivity of young leaf tissues to high-light stress.


Assuntos
Aldeídos/metabolismo , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Diterpenos/metabolismo , Estresse Fisiológico/fisiologia , Arabidopsis/efeitos dos fármacos , Proteínas de Arabidopsis/genética , Regulação da Expressão Gênica de Plantas , Inativação Metabólica , Luz , Mutação , Folhas de Planta/fisiologia , Plantas Geneticamente Modificadas , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Xenobióticos/farmacologia
9.
Plant J ; 2018 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-29901834

RESUMO

Prenylquinols (tocochromanols and plastoquinols) serve as efficient physical and chemical quenchers of singlet oxygen (1 O2 ) formed during high light stress in higher plants. Although quenching of 1 O2 by prenylquinols has been previously studied, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is limited in vivo. In the present study, the role of plastoquinol-9 (PQH2 -9) in chemical quenching of 1 O2 was studied in Arabidopsis thaliana lines overexpressing the SOLANESYL DIPHOSPHATE SYNTHASE 1 gene (SPS1oex) involved in PQH2 -9 and plastochromanol-8 biosynthesis. In this work, direct evidence for chemical quenching of 1 O2 by plastoquinols and their oxidation products is presented, which is obtained by microscopic techniques in vivo. Chemical quenching of 1 O2 was associated with consumption of PQH2 -9 and formation of its various oxidized forms. Oxidation of PQH2 -9 by 1 O2 leads to plastoquinone-9 (PQ-9), which is subsequently oxidized to hydroxyplastoquinone-9 [PQ(OH)-9]. We provide here evidence that oxidation of PQ(OH)-9 by 1 O2 results in the formation of trihydroxyplastoquinone-9 [PQ(OH)3 -9]. It is concluded here that PQH2 -9 serves as an efficient 1 O2 chemical quencher in Arabidopsis, and PQ(OH)3 -9 can be considered as a natural product of 1 O2 reaction with PQ(OH)-9. The understanding of the mechanisms underlying 1 O2 chemical quenching provides information on the role of plastoquinols and their oxidation products in the response of plants to photooxidative stress.

10.
Plant Cell Environ ; 41(10): 2299-2312, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29749622

RESUMO

The capacity of a Quercus pubescens forest to resist recurrent drought was assessed on an in situ experimental platform through the measurement of a large set of traits (ecophysiological and metabolic) studied under natural drought (ND) and amplified drought (AD) induced by partial rain exclusion. This study was performed during the third and fourth years of AD, which correspond to conditions of moderate AD in 2014 and harsher AD in 2015, respectively. Although water potential (Ψ) and net photosynthesis (Pn) were noticeably reduced under AD in 2015 compared to ND, trees showed similar growth and no oxidative stress. The absence of oxidative damage could be due to a strong accumulation of α-tocopherol, suggesting that this compound is a major component of the Q. pubescens antioxidant system. Other antioxidants were rather stable under AD in 2014, but slight changes started to be observed in 2015 (carotenoids and isoprene) due to harsher conditions. Our results indicate that Q. pubescens could be able to cope with AD, for at least 4 years, likely due to its antioxidant system. However, growth decrease was observed during the fifth year (2016) of AD, suggesting that this resistance could be threatened over longer periods of recurrent drought.


Assuntos
Quercus/metabolismo , Mudança Climática , Desidratação , Secas , Região do Mediterrâneo , Estresse Oxidativo , Fotossíntese , Quercus/fisiologia , Fatores de Tempo
11.
Plant Cell Environ ; 41(10): 2277-2287, 2018 10.
Artigo em Inglês | MEDLINE | ID: mdl-29601642

RESUMO

The Arabidopsis vte1 mutant is devoid of tocopherol and plastochromanol (PC-8). When exposed to excess light energy, vte1 produced more singlet oxygen (1 O2 ) and suffered from extensive oxidative damage compared with the wild type. Here, we show that overexpressing the solanesyl diphosphate synthase 1 (SPS1) gene in vte1 induced a marked accumulation of total plastoquinone (PQ-9) and rendered the vte1 SPS1oex plants tolerant to photooxidative stress, indicating that PQ-9 can replace tocopherol and PC-8 in photoprotection. High total PQ-9 levels were associated with a noticeable decrease in 1 O2 production and higher levels of Hydroxyplastoquinone (PQ-C), a 1 O2 -specific PQ-9 oxidation product. The extra PQ-9 molecules in the vte1 SPS1oex plants were stored in the plastoglobules and the chloroplast envelopes, rather than in the thylakoid membranes, whereas PQ-C was found almost exclusively in the thylakoid membranes. Upon exposure of wild-type plants to high light, the thylakoid PQ-9 pool decreased, whereas the extrathylakoid pool remained unchanged. In vte1 and vte1 SPS1oex plants, the PQ-9 losses in high light were strongly amplified, affecting also the extrathylakoid pool, and PQ-C was found in high amounts in the thylakoids. We conclude that the thylakoid PQ-9 pool acts as a 1 O2 scavenger and is replenished from the extrathylakoid stock.


Assuntos
Depuradores de Radicais Livres/metabolismo , Plastoquinona/metabolismo , Oxigênio Singlete/metabolismo , Tilacoides/metabolismo , Alquil e Aril Transferases/metabolismo , Proteínas de Arabidopsis/metabolismo , Clorofila/metabolismo , Cloroplastos/metabolismo , Cromatografia Líquida de Alta Pressão , Espectroscopia de Ressonância de Spin Eletrônica , Luz , Peroxidação de Lipídeos , Estresse Oxidativo/efeitos da radiação
12.
Plant Cell ; 30(1): 196-208, 2018 01.
Artigo em Inglês | MEDLINE | ID: mdl-29233855

RESUMO

Light utilization is finely tuned in photosynthetic organisms to prevent cellular damage. The dissipation of excess absorbed light energy, a process termed nonphotochemical quenching (NPQ), plays an important role in photoprotection. Little is known about the sustained or slowly reversible form(s) of NPQ and whether they are photoprotective, in part due to the lack of mutants. The Arabidopsis thaliana suppressor of quenching1 (soq1) mutant exhibits enhanced sustained NPQ, which we term qH. To identify molecular players involved in qH, we screened for suppressors of soq1 and isolated mutants affecting either chlorophyllide a oxygenase or the chloroplastic lipocalin, now renamed plastid lipocalin (LCNP). Analysis of the mutants confirmed that qH is localized to the peripheral antenna (LHCII) of photosystem II and demonstrated that LCNP is required for qH, either directly (by forming NPQ sites) or indirectly (by modifying the LHCII membrane environment). qH operates under stress conditions such as cold and high light and is photoprotective, as it reduces lipid peroxidation levels. We propose that, under stress conditions, LCNP protects the thylakoid membrane by enabling sustained NPQ in LHCII, thereby preventing singlet oxygen stress.


Assuntos
Arabidopsis/metabolismo , Lipocalinas/metabolismo , Processos Fotoquímicos , Plastídeos/metabolismo , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/metabolismo , Clorofila/metabolismo , Temperatura Baixa , Genes de Plantas , Genes Supressores , Testes Genéticos , Luz , Mutação/genética , Oxigenases/metabolismo , Processos Fotoquímicos/efeitos da radiação , Plastídeos/efeitos da radiação , Tiorredoxinas/metabolismo , Sequenciamento Completo do Genoma
13.
Plant Physiol ; 175(3): 1381-1394, 2017 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-28916593

RESUMO

Carnosic acid, a phenolic diterpene specific to the Lamiaceae family, is highly abundant in rosemary (Rosmarinus officinalis). Despite numerous industrial and medicinal/pharmaceutical applications of its antioxidative features, this compound in planta and its antioxidant mechanism have received little attention, except a few studies of rosemary plants under natural conditions. In vitro analyses, using high-performance liquid chromatography-ultraviolet and luminescence imaging, revealed that carnosic acid and its major oxidized derivative, carnosol, protect lipids from oxidation. Both compounds preserved linolenic acid and monogalactosyldiacylglycerol from singlet oxygen and from hydroxyl radical. When applied exogenously, they were both able to protect thylakoid membranes prepared from Arabidopsis (Arabidopsis thaliana) leaves against lipid peroxidation. Different levels of carnosic acid and carnosol in two contrasting rosemary varieties correlated with tolerance to lipid peroxidation. Upon reactive oxygen species (ROS) oxidation of lipids, carnosic acid was consumed and oxidized into various derivatives, including into carnosol, while carnosol resisted, suggesting that carnosic acid is a chemical quencher of ROS. The antioxidative function of carnosol relies on another mechanism, occurring directly in the lipid oxidation process. Under oxidative conditions that did not involve ROS generation, carnosol inhibited lipid peroxidation, contrary to carnosic acid. Using spin probes and electron paramagnetic resonance detection, we confirmed that carnosic acid, rather than carnosol, is a ROS quencher. Various oxidized derivatives of carnosic acid were detected in rosemary leaves in low light, indicating chronic oxidation of this compound, and accumulated in plants exposed to stress conditions, in parallel with a loss of carnosic acid, confirming that chemical quenching of ROS by carnosic acid takes place in planta.


Assuntos
Abietanos/farmacologia , Antioxidantes/farmacologia , Rosmarinus/metabolismo , Membranas Intracelulares/efeitos dos fármacos , Membranas Intracelulares/metabolismo , Peroxidação de Lipídeos/efeitos dos fármacos , Lipídeos/química , Oxirredução , Folhas de Planta/efeitos dos fármacos , Folhas de Planta/metabolismo , Folhas de Planta/ultraestrutura , Espécies Reativas de Oxigênio/metabolismo , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismo , Tilacoides/ultraestrutura , Fatores de Tempo , alfa-Tocoferol/farmacologia
14.
Plant Cell Physiol ; 58(5): 925-933, 2017 05 01.
Artigo em Inglês | MEDLINE | ID: mdl-28371855

RESUMO

Storage of seeds is accompanied by loss of germination and oxidation of storage and membrane lipids. A lipidomic analysis revealed that during natural and artificial aging of Arabidopsis seeds, levels of several diacylglycerols and free fatty acids, such as linoleic acid and linolenic acid as well as free oxidized fatty acids and oxygenated triacylglycerols, increased. Lipids can be oxidized by enzymatic or non-enzymatic processes. In the enzymatic pathway, lipoxygenases (LOXs) catalyze the first oxygenation step of polyunsaturated fatty acids. Analysis of lipid levels in mutants with defects in the two 9-LOX genes revealed that the strong increase in free 9-hydroxy- and 9-keto-fatty acids is dependent on LOX1 but not LOX5. Fatty acid oxidation correlated with an aging-induced decrease of germination, raising the question of whether these oxylipins negatively regulate germination. However, seeds of the lox1 mutant were only slightly more tolerant to aging, indicating that 9-LOX products contribute to but are not the major cause of loss of germination during aging. In contrast to free oxidized fatty acids, accumulation of oxygenated triacylglycerols upon accelerated aging was mainly based on non-enzymatic oxidation of seed storage lipids.


Assuntos
Arabidopsis/metabolismo , Sementes/enzimologia , Sementes/metabolismo , Arabidopsis/enzimologia , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Metabolismo dos Lipídeos/genética , Metabolismo dos Lipídeos/fisiologia , Lipoxigenase/genética , Lipoxigenase/metabolismo , Oxirredução , Sementes/fisiologia
15.
Plant Cell Environ ; 40(2): 216-226, 2017 02.
Artigo em Inglês | MEDLINE | ID: mdl-27813110

RESUMO

Singlet oxygen (1 O2 ) signalling in plants is essential to trigger both acclimatory mechanisms and programmed cell death under high light stress. However, because of its chemical features, 1 O2 requires mediators, and the players involved in this pathway are largely unknown. The ß-carotene oxidation product, ß-cyclocitral, is one such mediator. Produced in the chloroplast, ß-cyclocitral induces changes in nuclear gene expression leading to photoacclimation. Recently, the METHYLENE BLUE SENSITIVITY protein MBS has been identified as a key player in 1 O2 signalling leading to tolerance to high light. Here, we provide evidence that MBS1 is essential for acclimation to 1 O2 and cross-talks with ß-cyclocitral to mediate transfer of the 1 O2 signal to the nucleus, leading to photoacclimation. The presented results position MBS1 downstream of ß-cyclocitral in 1 O2 signalling and suggest an additional role for MBS1 in the regulation of plant growth and development under chronic 1 O2 production.


Assuntos
Aclimatação , Aldeídos/farmacologia , Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Diterpenos/farmacologia , Oxigênio Singlete/farmacologia , Aclimatação/efeitos da radiação , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Arabidopsis/efeitos da radiação , Proteínas de Arabidopsis/genética , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Proteínas de Fluorescência Verde/metabolismo , Luz , Mutação/genética , Fenótipo , Fotossíntese/efeitos da radiação , Folhas de Planta/fisiologia , Folhas de Planta/efeitos da radiação , Estresse Fisiológico/efeitos da radiação
16.
Plant Cell ; 28(7): 1616-39, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-27354555

RESUMO

The circadian clock helps plants measure daylength and adapt to changes in the day-night rhythm. We found that changes in the light-dark regime triggered stress responses, eventually leading to cell death, in leaves of Arabidopsis thaliana plants with reduced cytokinin levels or defective cytokinin signaling. Prolonged light treatment followed by a dark period induced stress and cell death marker genes while reducing photosynthetic efficiency. This response, called circadian stress, is also characterized by altered expression of clock and clock output genes. In particular, this treatment strongly reduced the expression of CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY). Intriguingly, similar changes in gene expression and cell death were observed in clock mutants lacking proper CCA1 and LHY function. Circadian stress caused strong changes in reactive oxygen species- and jasmonic acid (JA)-related gene expression. The activation of the JA pathway, involving the accumulation of JA metabolites, was crucial for the induction of cell death, since the cell death phenotype was strongly reduced in the jasmonate resistant1 mutant background. We propose that adaptation to circadian stress regimes requires a normal cytokinin status which, acting primarily through the AHK3 receptor, supports circadian clock function to guard against the detrimental effects of circadian stress.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Morte Celular/fisiologia , Relógios Circadianos/fisiologia , Ciclopentanos/metabolismo , Citocininas/metabolismo , Oxilipinas/metabolismo , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Morte Celular/genética , Relógios Circadianos/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Regulação da Expressão Gênica de Plantas/genética , Regulação da Expressão Gênica de Plantas/fisiologia , Luz , Espécies Reativas de Oxigênio/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo
17.
Plant Physiol ; 171(3): 1734-49, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-27288360

RESUMO

Distinct ROS signaling pathways initiated by singlet oxygen ((1)O2) or superoxide and hydrogen peroxide have been attributed to either cell death or acclimation, respectively. Recent studies have revealed that more complex antagonistic and synergistic relationships exist within and between these pathways. As specific chloroplastic ROS signals are difficult to study, rapid systemic signaling experiments using localized high light (HL) stress or ROS treatments were used in this study to uncouple signals required for direct HL and ROS perception and distal systemic acquired acclimation (SAA). A qPCR approach was chosen to determine local perception and distal signal reception. Analysis of a thylakoidal ascorbate peroxidase mutant (tapx), the (1)O2-retrograde signaling double mutant (ex1/ex2), and an apoplastic signaling double mutant (rbohD/F) revealed that tAPX and EXECUTER 1 are required for both HL and systemic acclimation stress perception. Apoplastic membrane-localized RBOHs were required for systemic spread of the signal but not for local signal induction in directly stressed tissues. Endogenous ROS treatments revealed a very strong systemic response induced by a localized 1 h induction of (1)O2 using the conditional flu mutant. A qPCR time course of (1)O2 induced systemic marker genes in directly and indirectly connected leaves revealed a direct vascular connection component of both immediate and longer term SAA signaling responses. These results reveal the importance of an EXECUTER-dependent (1)O2 retrograde signal for both local and long distance RBOH-dependent acclimation signaling that is distinct from other HL signaling pathways, and that direct vascular connections have a role in spatial-temporal SAA induction.


Assuntos
Aclimatação/fisiologia , Arabidopsis/fisiologia , Oxigênio Singlete/metabolismo , Aldeídos/metabolismo , Antocianinas/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Ascorbato Peroxidases/genética , Ascorbato Peroxidases/metabolismo , Diterpenos/metabolismo , Regulação da Expressão Gênica de Plantas , Luz , Mutação , Folhas de Planta/fisiologia , Plantas Geneticamente Modificadas , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo
18.
Plant Physiol ; 170(3): 1757-71, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26747288

RESUMO

Studies of the singlet oxygen ((1)O2)-overproducing flu and chlorina1 (ch1) mutants of Arabidopsis (Arabidopsis thaliana) have shown that (1)O2-induced changes in gene expression can lead to either programmed cell death (PCD) or acclimation. A transcriptomic analysis of the ch1 mutant has allowed the identification of genes whose expression is specifically affected by each phenomenon. One such gene is OXIDATIVE SIGNAL INDUCIBLE1 (OXI1) encoding an AGC kinase that was noticeably induced by excess light energy and (1)O2 stress conditions leading to cell death. Photo-induced oxidative damage and cell death were drastically reduced in the OXI1 null mutant (oxi1) and in the double mutant ch1*oxi1 compared with the wild type and the ch1 single mutant, respectively. This occurred without any changes in the production rate of (1)O2 but was cancelled by exogenous applications of the phytohormone jasmonate. OXI1-mediated (1)O2 signaling appeared to operate through a different pathway from the previously characterized OXI1-dependent response to pathogens and H2O2 and was found to be independent of the EXECUTER proteins. In high-light-stressed plants, the oxi1 mutation was associated with reduced jasmonate levels and with the up-regulation of genes encoding negative regulators of jasmonate signaling and PCD. Our results show that OXI1 is a new regulator of (1)O2-induced PCD, likely acting upstream of jasmonate.


Assuntos
Apoptose/genética , Proteínas de Arabidopsis/genética , Arabidopsis/genética , Regulação da Expressão Gênica de Plantas/genética , Proteínas Serina-Treonina Quinases/genética , Oxigênio Singlete/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Ciclopentanos/farmacologia , Perfilação da Expressão Gênica/métodos , Regulação da Expressão Gênica de Plantas/efeitos dos fármacos , Regulação da Expressão Gênica de Plantas/efeitos da radiação , Luz , Modelos Genéticos , Mutação , Análise de Sequência com Séries de Oligonucleotídeos , Oxilipinas/farmacologia , Complexo de Proteína do Fotossistema II/genética , Complexo de Proteína do Fotossistema II/metabolismo , Reguladores de Crescimento de Planta/farmacologia , Proteínas Serina-Treonina Quinases/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/genética , Transdução de Sinais/efeitos da radiação
19.
Sci Rep ; 5: 10919, 2015 Jun 03.
Artigo em Inglês | MEDLINE | ID: mdl-26039552

RESUMO

Plastoquinone-9 is known as a photosynthetic electron carrier to which has also been attributed a role in the regulation of gene expression and enzyme activities via its redox state. Here, we show that it acts also as an antioxidant in plant leaves, playing a central photoprotective role. When Arabidopsis plants were suddenly exposed to excess light energy, a rapid consumption of plastoquinone-9 occurred, followed by a progressive increase in concentration during the acclimation phase. By overexpressing the plastoquinone-9 biosynthesis gene SPS1 (solanesyl diphosphate synthase 1) in Arabidopsis, we succeeded in generating plants that specifically accumulate plastoquinone-9 and its derivative plastochromanol-8. The SPS1-overexpressing lines were much more resistant to photooxidative stress than the wild type, showing marked decreases in leaf bleaching, lipid peroxidation and PSII photoinhibition under excess light. Comparison of the SPS1 overexpressors with other prenyl quinone mutants indicated that the enhanced phototolerance of the former plants is directly related to their increased capacities for plastoquinone-9 biosynthesis.


Assuntos
Adaptação Biológica , Luz , Estresse Oxidativo , Fotossíntese , Fenômenos Fisiológicos Vegetais , Plastoquinona/metabolismo , Arabidopsis/fisiologia , Arabidopsis/efeitos da radiação , Vias Biossintéticas , Regulação da Expressão Gênica de Plantas , Mutação , Fenótipo , Folhas de Planta/metabolismo
20.
Front Plant Sci ; 6: 39, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25699067

RESUMO

The production of reactive oxygen species (ROS) is an unavoidable consequence of oxygenic photosynthesis. Singlet oxygen ((1)O2) is a highly reactive species to which has been attributed a major destructive role during the execution of ROS-induced cell death in photosynthetic tissues exposed to excess light. The study of the specific biological activity of (1)O2 in plants has been hindered by its high reactivity and short lifetime, the concurrent production of other ROS under photooxidative stress, and limited in vivo detection methods. However, during the last 15 years, the isolation and characterization of two (1)O2-overproducing mutants in Arabidopsis thaliana, flu and ch1, has allowed the identification of genetically controlled (1)O2 cell death pathways and a (1)O2 acclimation pathway that are triggered at sub-cytotoxic concentrations of (1)O2. The study of flu has revealed the control of cell death by the plastid proteins EXECUTER (EX)1 and EX2. In ch1, oxidized derivatives of ß-carotene, such as ß-cyclocitral and dihydroactinidiolide, have been identified as important upstream messengers in the (1)O2 signaling pathway that leads to stress acclimation. In both the flu and ch1 mutants, phytohormones act as important promoters or inhibitors of cell death. In particular, jasmonate has emerged as a key player in the decision between acclimation and cell death in response to (1)O2. Although the flu and ch1 mutants show many similarities, especially regarding their gene expression profiles, key differences, such as EXECUTER-independent cell death in ch1, have also been observed and will need further investigation to be fully understood.

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