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Margaret Ahmad - One of the best experts on this subject based on the ideXlab platform.
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magnetic sensitivity mediated by the arabidopsis blue light receptor Cryptochrome occurs during flavin reoxidation in the dark
Planta, 2019Co-Authors: Marootpong Pooam, Margaret Ahmad, Justin Link, Louisdavid Arthaut, Derek Burdick, Carlos F MartinoAbstract:MAIN CONCLUSION: Arabidopsis Cryptochrome mediates responses to magnetic fields that have been applied in the absence of light, consistent with flavin reoxidation as the primary detection mechanism. Cryptochromes are highly conserved blue-light-absorbing flavoproteins which have been linked to the perception of electromagnetic stimuli in numerous organisms. These include sensing the direction of the earth's magnetic field in migratory birds and the intensity of magnetic fields in insects and plants. When exposed to light, Cryptochromes undergo flavin reduction/reoxidation redox cycles leading to biological activation which generate radical pairs thought to be the basis for magnetic sensitivity. However, the nature of the magnetically sensitive radical pairs and the steps at which they act during the Cryptochrome redox cycle are currently a matter of debate. Here, we investigate the response of Arabidopsis Cryptochrome-1 in vivo to a static magnetic field of 500 μT (10 × earth's field) using both plant growth and light-dependent phosphorylation as an assay. Cryptochrome responses to light were enhanced by the magnetic field, as indicated by increased inhibition of hypocotyl elongation and increased Cryptochrome phosphorylation. However, when light and dark intervals were given intermittently, a plant response to the magnetic field was observed even when the magnetic field was given exclusively during the dark intervals between light exposures. This indicates that the magnetically sensitive reaction step in the Cryptochrome photocycle must occur during flavin reoxidation, and likely involves the formation of reactive oxygen species.
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hy5 is a point of convergence between Cryptochrome and cytokinin signalling pathways in arabidopsis thaliana
Plant Journal, 2007Co-Authors: Margaret Ahmad, Yvette Habricot, Amanda S Condiff, Regis Maldiney, Filip Vandenbussche, Dominique Van Der StraetenAbstract:Summary Blue-light-dependent photomorphogenesis in Arabidopsis is regulated principally by the Cryptochrome flavin-type photoreceptors, which control hypocotyl growth inhibition, cotyledon and leaf expansion, and the expression of light-regulated genes. Interestingly the plant hormone cytokinin induces similar responses when added exogenously to germinating seedlings, suggesting a link between Cryptochrome and cytokinin signalling pathways. In this work we explore the relationship between Cryptochrome and cytokinin signalling pathways in the promotion of photomorphogenesis. The effect of exogenously added cytokinins on hypocotyl growth inhibition occurs in the dark, and is largely independent and additive to that of Cryptochromes in blue light, via distinct signalling pathways. By contrast, cytokinin-dependent stimulation of anthocyanin accumulation occurs only in light, and interacts with the signalling pathway downstream of Cryptochrome 1 (CRY1) at the level of transcript accumulation of anthocyanin biosynthetic genes. Mutants in elongated hypocotyl 5 (hy5), a downstream intermediate in the CRY1 signalling pathway, show a reduced induction of anthocyanin accumulation in blue light by cytokinins, similar to that observed for Cryptochrome (cry1) mutants. Furthermore cytokinins are shown to increase levels of HY5 protein accumulation, suggesting that cytokinins may function by reducing HY5 degradation by COP1 (constitutively photomorphogenic 1). As both Cryptochrome and cytokinin signalling pathways increase HY5 protein levels, and as HY5 binds to the promoters of anthocyanin biosynthetic enzymes to stimulate gene expression, it is concluded that the regulation of HY5 protein stability represents a point of convergence between Cryptochrome and cytokinin signalling pathways.
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light induced electron transfer in arabidopsis Cryptochrome 1 correlates with in vivo function
Journal of Biological Chemistry, 2005Co-Authors: Anke Zeugner, Nadia Bakrim, Baldissera Giovani, Martin Byrdin, Klaus Brettel, Jean-pierre Bouly, Margaret AhmadAbstract:Abstract Cryptochromes are blue light-activated photoreceptors found in multiple organisms with significant similarity to photolyases, a class of light-dependent DNA repair enzymes. Unlike photolyases, Cryptochromes do not repair DNA and instead mediate blue light-dependent developmental, growth, and/or circadian responses by an as yet unknown mechanism of action. It has recently been shown that Arabidopsis Cryptochrome-1 retains photolyase-like photoreduction of its flavin cofactor FAD by intraprotein electron transfer from tryptophan and tyrosine residues. Here we demonstrate that substitution of two conserved tryptophans that are constituents of the flavin-reducing electron transfer chain in Escherichia coli photolyase impairs light-induced electron transfer in the Arabidopsis Cryptochrome-1 photoreceptor in vitro. Furthermore, we show that these substitutions result in marked reduction of light-activated autophosphorylation of Cryptochrome-1 in vitro and of its photoreceptor function in vivo, consistent with biological relevance of the electron transfer reaction. These data support the possibility that light-induced flavin reduction via the tryptophan chain is the primary step in the signaling pathway of plant Cryptochrome.
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light induced electron transfer in a Cryptochrome blue light photoreceptor
Nature Structural & Molecular Biology, 2003Co-Authors: Margaret Ahmad, Baldissera Giovani, Martin Byrdin, Klaus BrettelAbstract:Cryptochromes are flavoproteins implicated in multiple blue light–dependent signaling pathways regulating, for example, photomorphogenesis in plants or circadian clocks in animals. Using transient absorption spectroscopy, it is demonstrated that the primary light reactions in isolated Arabidopsis thaliana Cryptochrome-1 involve intraprotein electron transfer from tryptophan and tyrosine residues to the excited flavin adenine dinucleotide cofactor. *Note: The version of this paper initially published online was incorrectly labeled as an 'Article'; the correct category should be 'Brief Communication'. We apologize for any inconvenience this may have caused. This mistake has been corrected in the HTML and print version of the paper.
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Cryptochrome blue light photoreceptors of arabidopsis implicated in phototropism
Nature, 1998Co-Authors: Margaret Ahmad, Jose A Jarillo, Olga Smirnova, Anthony R CashmoreAbstract:Phototropism — bending towards the light — is one of the best known plant tropic responses1,2. Despite being reported by Darwin and others3,4 over a century ago to be specifically under the control of blue light, the photoreceptors mediating phototropism have remained unknown. We have characterized a blue-light photoreceptor from Arabidopsis, named CRY1 for Cryptochrome 1 (ref. 5); this photoreceptor is a flavoprotein that mediates numerous blue-light-dependent responses6. In Arabidopsis, HY4 (the gene encoding CRY1) is a member of a small gene family that also encodes a related photoreceptor, CRY2 (refs 7, 8), which shares considerable functional overlap with CRY1 (ref. 9). Here we report that mutant plants lacking both the CRY1 and the CRY2 blue-light photoreceptors are deficient in the phototropic response. Transgenic Arabidopsis plants overexpressing CRY1 or CRY2 show enhanced phototropic curvature. We conclude that Cryptochrome is one of the photoreceptors mediating phototropism in plants.
Jorge J. Casal - One of the best experts on this subject based on the ideXlab platform.
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in arabidopsis low blue light enhances phototropism by releasing Cryptochrome 1 mediated inhibition of pif4 expression
bioRxiv, 2020Co-Authors: Alessandra Boccaccini, Jorge J. Casal, Anupama Goyal, Elizabeth Karayekov, Martina Legris, Johanna Krahmer, Teva Vernoux, Laure Allenbachpetrolati, Carlos GalvanampudiaAbstract:Abstract Shade-avoiding plants including Arabidopsis thaliana display a number of growth responses elicited by shade cues including elongation of stem-like structures and repositioning of leaves. Shade also promotes phototropism of de-etiolated seedlings through repression of phytochrome B (phyB) presumably to enhance capture of unfiltered sunlight. Light cues indicative of shade include a reduction in the blue and red portions of the solar spectrum and a low red to far-red ratio. Here we show that in Arabidopsis seedlings both low blue and a low red to far-red ratio are required to rapidly enhance phototropism. However, prolonged low blue treatments through reduced Cryptochrome 1 (cry1) activation are sufficient to promote phototropism. The enhanced phototropic response of cry1 mutants in the lab and in response to natural canopies depends on PHYTOCHROME INTERACTING FACTORs (PIFs). In favorable light conditions, cry1 limits the expression of PIF4 while in low blue light PIF4 expression increases, which contributes to phototropic enhancement. The analysis of a quantitative DII auxin reporter indicates that low blue light leads to enhanced auxin levels in the hypocotyl and, upon phototropic stimulation, a steeper auxin gradient across the hypocotyl. We conclude that phototropic enhancement by canopy shade results from the combined activities of phytochrome B and cry1 that converge on PIF regulation. ONE SENTENCE SUMMARY The persistent depletion of blue light in natural canopy shade relieves the inhibitory effect of Cryptochrome 1 on PIF4, enhancing phototropism in de-etiolated Arabidopsis seedlings. Financial support This work was supported by the University of Lausanne and a grant from the Swiss National Science foundation (n° 310030B_179558 to C.F.); Human Frontier Science Program organization (HFSP) Grant RPG0054-2013, ANR-12-BSV6-0005 grant (AuxiFlo) to T.V.; The University of Buenos Aires (Grant 20020100100437 to J. J. C.), and Agencia Nacional de Promocion Cientifica y Tecnologica of Argentina (Grant PICT-2018-01695 to J. J. C.). Alessandra Boccaccini and Martina Legris are funded by Marie Curie fellowships H2020-MSCA-IF-2017 grants CRoSh 796283 and Flat-Leaf 796443 respectively.
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Photoreceptor-mediated kin recognition in plants
New Phytologist, 2015Co-Authors: María A. Crepy, Jorge J. CasalAbstract:Although cooperative interactions among kin have been established in a variety of biological systems, their occurrence in plants remains controversial. Plants of Arabidopsis thaliana were grown in rows of either a single or multiple accessions. Plants recognized kin neighbours and horizontally reoriented leaf growth, a response not observed when plants were grown with nonkin. Plant kin recognition involved the perception of the vertical red/far-red light and blue light profiles. Disruption of the light profiles, mutations at the PHYTOCHROME B, Cryptochrome 1 or 2, or PHOTOTROPIN 1 or 2 photoreceptor genes or mutations at the TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 gene required for auxin (growth hormone) synthesis impaired the response. The leaf-position response increases plant self-shading, decreases mutual shading between neighbours and increases fitness. Light signals from neighbours are known to shape a more competitive plant body. Here we show that photosensory receptors mediate cooperative rather than competitive interactions among kin neighbours by reducing the competition for local pools of resources.
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hierarchical coupling of phytochromes and Cryptochromes reconciles stability and light modulation of arabidopsis development
Development, 2001Co-Authors: Maria Agustina Mazzella, Pablo D Cerdan, Roberto J Staneloni, Jorge J. CasalAbstract:In plants, development is a continuing process that takes place under strong fluctuations of the light environment. Here we show that in Arabidopsis thaliana plants grown under intense white light, coupling of the photoreceptor Cryptochrome 2 to developmental processes is broader than previously appreciated. Compared to the wild type, the cry2 mutant showed reduced activity of a Lhcb1*2 promoter fused to a reporter, and delayed flowering. The cry2 mutation also reduced the inhibition of hypocotyl growth, the unfolding of the cotyledons, the rate of leaf production during the vegetative phase, and the pace of development after transition to the reproductive stage; but these effects were obvious only in the absence of Cryptochrome 1 and in some cases phytochrome A and/or phytochrome B. Complementary, the cry2 mutation uncovered novel roles for Cryptochrome 1 and phytochrome A. The activity of the Lhcb1*2 promoter was higher in the cry1 cry2 mutant than in the cry2 mutant, suggesting that cry1 could be involved in blue-light repression of photosynthetic genes. Surprisingly, the phyA cry1 cry2 triple mutant flowered earlier and showed better response to photoperiod than the cry1 cry2 double mutant, indicating that phyA is involved in light repression of flowering. Growth and development were severely impaired in the quadruple phyA phyB cry1 cry2 mutant. We propose that stability and light modulation of development are achieved by simultaneous coupling of phytochrome A, phytochrome B, Cryptochrome 1 and Cryptochrome 2 to developmental processes, in combination with context-dependent hierarchy of their relative activities.
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interactive signalling by phytochromes and Cryptochromes generates de etiolation homeostasis in arabidopsis thaliana
Plant Cell and Environment, 2001Co-Authors: Maria Agustina Mazzella, Jorge J. CasalAbstract:ABSTRACT Single, double, triple and quadruple mutants of phyA , phyB , cry1 and cry2 were exposed to different sunlight irra-diances and photoperiods to investigate the roll played byphytochrome A, phytochrome B, Cryptochrome 1 and cryp-tochrome 2 during de-etiolation of Arabidopsis thaliana seedlings under natural radiation. Even the quadruplemutant retained some hypocotyl-growth inhibition by sun-light. Hypocotyl length was strongly affected by interac-tions among photoreceptors. Double phyA phyB , phyAcry1 , and cry1 cry2 mutants were taller than expected fromthe additive action of single mutations. Some of theseredundant interactions required the presence of phy-tochromes A and/or B. Interactions among photoreceptorsresulted in a 44% reduction of the response to irradianceand a 70% reduction of the response to photoperiod. Thecomplex network of interactions among photoreceptors isproposed to buffer de-etiolation against changes in irradi-ance and photoperiod, i.e light fluctuations not related tothe positions of the shoot above or below soil level
Klaus Brettel - One of the best experts on this subject based on the ideXlab platform.
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atp binding turns plant Cryptochrome into an efficient natural photoswitch
Scientific Reports, 2015Co-Authors: Pavel Muller, Veronique Balland, Kenichi Hitomi, Thorsten Ritz, Jean-pierre Bouly, Elizabeth D. Getzoff, Klaus BrettelAbstract:Cryptochromes are flavoproteins that drive diverse developmental light-responses in plants and participate in the circadian clock in animals. Plant Cryptochromes have found application as photoswitches in optogenetics. We have studied effects of pH and ATP on the functionally relevant photoreduction of the oxidized FAD cofactor to the semi-reduced FADH ? radical in isolated Arabidopsis Cryptochrome 1 by transient absorption spectroscopy on nanosecond to millisecond timescales. In the absence of ATP, the yield of light-induced radicals strongly decreased with increasing pH from 6.5 to 8.5. With ATP present, these yields were significantly higher and virtually pH-independent up to pH 9. Analysis of our data in light of the crystallographic structure suggests that ATP-binding shifts the pK a of aspartic acid D396, the putative proton donor to FAD? 2 , from ,7.4 to .9, and favours a reaction pathway yielding long-lived aspartate D396 2. Its negative charge could trigger conformational changes necessary for signal transduction.
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light induced electron transfer in arabidopsis Cryptochrome 1 correlates with in vivo function
Journal of Biological Chemistry, 2005Co-Authors: Anke Zeugner, Nadia Bakrim, Baldissera Giovani, Martin Byrdin, Klaus Brettel, Jean-pierre Bouly, Margaret AhmadAbstract:Abstract Cryptochromes are blue light-activated photoreceptors found in multiple organisms with significant similarity to photolyases, a class of light-dependent DNA repair enzymes. Unlike photolyases, Cryptochromes do not repair DNA and instead mediate blue light-dependent developmental, growth, and/or circadian responses by an as yet unknown mechanism of action. It has recently been shown that Arabidopsis Cryptochrome-1 retains photolyase-like photoreduction of its flavin cofactor FAD by intraprotein electron transfer from tryptophan and tyrosine residues. Here we demonstrate that substitution of two conserved tryptophans that are constituents of the flavin-reducing electron transfer chain in Escherichia coli photolyase impairs light-induced electron transfer in the Arabidopsis Cryptochrome-1 photoreceptor in vitro. Furthermore, we show that these substitutions result in marked reduction of light-activated autophosphorylation of Cryptochrome-1 in vitro and of its photoreceptor function in vivo, consistent with biological relevance of the electron transfer reaction. These data support the possibility that light-induced flavin reduction via the tryptophan chain is the primary step in the signaling pathway of plant Cryptochrome.
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light induced electron transfer in a Cryptochrome blue light photoreceptor
Nature Structural & Molecular Biology, 2003Co-Authors: Margaret Ahmad, Baldissera Giovani, Martin Byrdin, Klaus BrettelAbstract:Cryptochromes are flavoproteins implicated in multiple blue light–dependent signaling pathways regulating, for example, photomorphogenesis in plants or circadian clocks in animals. Using transient absorption spectroscopy, it is demonstrated that the primary light reactions in isolated Arabidopsis thaliana Cryptochrome-1 involve intraprotein electron transfer from tryptophan and tyrosine residues to the excited flavin adenine dinucleotide cofactor. *Note: The version of this paper initially published online was incorrectly labeled as an 'Article'; the correct category should be 'Brief Communication'. We apologize for any inconvenience this may have caused. This mistake has been corrected in the HTML and print version of the paper.
Suleyman I Allakhverdiev - One of the best experts on this subject based on the ideXlab platform.
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impact of high irradiance and uv b on the photosynthetic activity pro antioxidant balance and expression of light activated genes in arabidopsis thaliana hy4 mutants grown under blue light
Plant Physiology and Biochemistry, 2021Co-Authors: Vladimir D Kreslavski, Aleksandra Yu Khudyakova, G N Shirshikova, Pavel P Pashkovskiy, Vladimir V Kuznetsov, Valeria V Strokina, Tamara I Balakhnina, A A Kosobryukhov, Suleyman I AllakhverdievAbstract:Abstract The impacts of high-intensity light (HIL) (4 h) and UV-B radiation (1 h) on the photosynthetic activity, content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes (ascorbate peroxidase (APX) and guaiacol-dependent peroxidase (GPX)), content of thiobarbituric acid reactive substances (TBARs), expression of some light-regulated genes in 25-day-old wild type (WT) and the Cryptochrome 1 (Cry1) hy4 mutant of A. thaliana Col-0 plants grown under blue light (BL) were studied. HIL and UV-B treatments led to decreases in the photosynthetic rate (Pn), photochemical activity of PSII (FV/FM) and PSII performance index (PIABS) of WT and mutant plants grown under high-intensity BL (HBL) and moderate intensity BL (MBL). However, in HBL plants, the decrease in the photosynthetic activity in hy4 plants was significantly greater than that in WT plants. In addition, hy4 HBL plants demonstrated lowered UAP and carotenoid contents as well as lower activity of APX and GPX enzymes. The difference in the decline in the photosynthetic activity of WT and hy4 plants grown at MBL in response to HIL was nonsignificant, while that in response to UV-B was small. We assume that the deficiency in Cryptochrome 1 under HIL irradiation disrupts the interaction between HY5 and HFR1 transcription factors and photoreceptors, which affects the transcription of light-induced genes, such as CAB1, PSY and PAL1 linked to carotenoid and flavonoid biosynthesis. It was concluded that PA stress resistance in WT and hy4 plants depends on the light intensity and reduced stress resistance of hy4 at HBL, is likely linked to low UAP and carotenoid contents as well as lowered APX and GPX enzyme activities in hy4 mutants.
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impact of uv b radiation on the photosystem ii activity pro antioxidant balance and expression of light activated genes in arabidopsis thaliana hy4 mutants grown under light of different spectral composition
Journal of Photochemistry and Photobiology B-biology, 2019Co-Authors: Aleksandra Yu Khudyakova, Vladimir D Kreslavski, Aleksandr N Shmarev, Valery Yu Lyubimov, G N Shirshikova, Pavel P Pashkovskiy, Vladimir V Kuznetsov, Suleyman I AllakhverdievAbstract:Abstract The effect of UV-B irradiation on the photosystem II (PSII) activity, the content of photosynthetic and UV-absorbing pigments (UAPs), activity of antioxidant enzymes such as catalase (CAT) and peroxidase (POD), as well as H2O2 content in 25-day-old wild type (WT) and the Cryptochrome 1 (Cry1) mutant hy4 of Arabidopsis thaliana Col-0 plants was studied. In addition, expression of photoreceptor genes Cry1, Cry2 and UVR8, photomorphogenetic gene COP1 and transcription factors genes HY5, HYH, the gene of chlorophyll-binding protein of the PSII CAB1 as well as the flavonoid biosynthesis genes CHS, PAL and thylakoid ascorbate peroxidase gene tAPX was examined. It has been shown that UV-B leads to a decrease in the photochemical activity of PSII (FV/FM) and the PSII performance index (PIABS) of WT plants grown on white (WL) and red (RL) light and also hy4 mutants grown on WL, RL and blue light (BL). In plants grown on BL and WL, the decrease in the PSII photochemical activity was significantly greater in hy4 compared to WT. The PSII of WT plants grown in BL was resistant to UV-B. The UAPs content of hy4 grown on BL and WL was lower than that in WT. The POD and CAT activities of WT grown in BL were significantly higher than in the mutant. In WT and hy4 plants grown in RL, a noticeable difference in these enzymes activity was not found. In both types of plants grown in BL and RL, the expression of photomorphogenetic genes HYH, HY5 markedly increased after UV-B treatment but the expression of the UV-B photoreceptor gene UVR8 was reduced in hy4 grown in BL and RL. It is assumed that reduced resistance of PSII in hy4 plants grown in BL and WL can be associated with low UAPs content as well as lowered POD and CAT activities. In addition, we suggest the lowered expression of UVR8 and COP1 genes caused by Cry1 deficiency leads to a shift of balance of oxidants and antioxidants towards oxidants.
Baldissera Giovani - One of the best experts on this subject based on the ideXlab platform.
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light induced electron transfer in arabidopsis Cryptochrome 1 correlates with in vivo function
Journal of Biological Chemistry, 2005Co-Authors: Anke Zeugner, Nadia Bakrim, Baldissera Giovani, Martin Byrdin, Klaus Brettel, Jean-pierre Bouly, Margaret AhmadAbstract:Abstract Cryptochromes are blue light-activated photoreceptors found in multiple organisms with significant similarity to photolyases, a class of light-dependent DNA repair enzymes. Unlike photolyases, Cryptochromes do not repair DNA and instead mediate blue light-dependent developmental, growth, and/or circadian responses by an as yet unknown mechanism of action. It has recently been shown that Arabidopsis Cryptochrome-1 retains photolyase-like photoreduction of its flavin cofactor FAD by intraprotein electron transfer from tryptophan and tyrosine residues. Here we demonstrate that substitution of two conserved tryptophans that are constituents of the flavin-reducing electron transfer chain in Escherichia coli photolyase impairs light-induced electron transfer in the Arabidopsis Cryptochrome-1 photoreceptor in vitro. Furthermore, we show that these substitutions result in marked reduction of light-activated autophosphorylation of Cryptochrome-1 in vitro and of its photoreceptor function in vivo, consistent with biological relevance of the electron transfer reaction. These data support the possibility that light-induced flavin reduction via the tryptophan chain is the primary step in the signaling pathway of plant Cryptochrome.
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light induced electron transfer in a Cryptochrome blue light photoreceptor
Nature Structural & Molecular Biology, 2003Co-Authors: Margaret Ahmad, Baldissera Giovani, Martin Byrdin, Klaus BrettelAbstract:Cryptochromes are flavoproteins implicated in multiple blue light–dependent signaling pathways regulating, for example, photomorphogenesis in plants or circadian clocks in animals. Using transient absorption spectroscopy, it is demonstrated that the primary light reactions in isolated Arabidopsis thaliana Cryptochrome-1 involve intraprotein electron transfer from tryptophan and tyrosine residues to the excited flavin adenine dinucleotide cofactor. *Note: The version of this paper initially published online was incorrectly labeled as an 'Article'; the correct category should be 'Brief Communication'. We apologize for any inconvenience this may have caused. This mistake has been corrected in the HTML and print version of the paper.