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Tatsuya Sakai - One of the best experts on this subject based on the ideXlab platform.
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Low-fluence blue light-induced phosphorylation of Zmphot1 mediates the first positive Phototropism.
Journal of experimental botany, 2019Co-Authors: Hiromi Suzuki, Tomokazu Koshiba, Chiharu Fujita, Yoshio Yamauchi, Taro Kimura, Toshiaki Isobe, Tatsuya Sakai, Masato Taoka, Takashi OkamotoAbstract:Phototropin1 (phot1) perceives low- to high-fluence blue light stimuli and mediates both the first and second positive Phototropisms. High-fluence blue light is known to induce autophosphorylation of phot1, leading to the second positive Phototropism. However, the phosphorylation status of phot1 by low-fluence blue light that induces the first positive Phototropism had not been observed. Here, we conducted a phosphoproteomic analysis of maize coleoptiles to investigate the fluence-dependent phosphorylation status of Zmphot1. High-fluence blue light induced phosphorylation of Zmphot1 at several sites. Notably, low-fluence blue light significantly increased the phosphorylation level of Ser291 in Zmphot1. Furthermore, Ser291-phosphorylated and Ser369Ser376-diphosphorylated peptides were found to be more abundant in the low-fluence blue light-irradiated sides than in the shaded sides of coleoptiles. The roles of these phosphorylation events in Phototropism were explored by heterologous expression of ZmPHOT1 in the Arabidopsis thaliana phot1phot2 mutant. The first positive Phototropism was restored in wild-type ZmPHOT1-expressing plants; however, plants expressing S291A-ZmPHOT1 or S369AS376A-ZmPHOT1 showed significantly reduced complementation rates. All transgenic plants tested in this study exhibited a normal second positive Phototropism. These findings provide the first indication that low-fluence blue light induces phosphorylation of Zmphot1 and that this induced phosphorylation is crucial for the first positive Phototropism.
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Deetiolation Enhances Phototropism by Modulating NON-PHOTOTROPIC HYPOCOTYL3 Phosphorylation Status.
Plant physiology, 2019Co-Authors: Stuart Sullivan, Eros Kharshiing, Tatsuya Sakai, Janet Laird, John M. ChristieAbstract:Phototropin (phot) receptor kinases play important roles in promoting plant growth by controlling light-capturing processes, such as Phototropism. Phototropism is mediated through the action of NON-PHOTOTROPIC HYPOCOTYL3 (NPH3), which is dephosphorylated following phot activation. However, the functional significance of this early signaling event remains unclear. Here, we show that the onset of Phototropism in dark-grown (etiolated) seedlings of Arabidopsis (Arabidopsis thaliana) and tomato (Solanum lycopersicum) is enhanced by greening (deetiolation). Red and blue light were equally effective in promoting Phototropism in Arabidopsis, consistent with our observations that deetiolation by phytochrome or cryptochrome was sufficient to enhance Phototropism. Increased responsiveness did not result from an enhanced sensitivity to the phytohormone auxin, nor does it involve the phot-interacting protein, ROOT Phototropism2. Instead, deetiolated seedlings showed attenuated levels of NPH3 dephosphorylation and diminished relocalization of NPH3 from the plasma membrane during Phototropism. Likewise, etiolated seedlings that lack the PHYTOCHROME-INTERACTING FACTORS (PIFs) PIF1, PIF3, PIF4, and PIF5 displayed reduced NPH3 dephosphorylation and enhanced Phototropism, consistent with their constitutive photomorphogenic phenotype in darkness. Phototropic enhancement could also be achieved in etiolated seedlings by lowering the light intensity to diminish NPH3 dephosphorylation. Thus, Phototropism is enhanced following deetiolation through the modulation of a phosphorylation rheostat, which in turn sustains the activity of NPH3. We propose that this dynamic mode of regulation enables young seedlings to maximize their establishment under changing light conditions, depending on their photoautotrophic capacity.
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Roles of AGCVIII Kinases in the Hypocotyl Phototropism of Arabidopsis Seedlings.
Plant & cell physiology, 2018Co-Authors: Ken Haga, Taro Kimura, Lena Frank, Claus Schwechheimer, Tatsuya SakaiAbstract:Regulation of protein function by phosphorylation and dephosphorylation is an important mechanism in many cellular events. The phototropin blue-light photoreceptors, plant-specific AGCVIII kinases, are essential for phototropic responses. Members of the D6 PROTEIN KINASE (D6PK) family, representing a subfamily of the AGCVIII kinases, also contribute to phototropic responses, suggesting that possibly further AGCVIII kinases may potentially control Phototropism. The present study investigates the functional roles of Arabidopsis (Arabidopsis thaliana) AGCVIII kinases in hypocotyl Phototropism. We demonstrate that D6PK family kinases are not only required for the second but also for the first positive Phototropism. In addition, we find that a previously uncharacterized AGCVIII protein, AGC1-12, is involved in the first positive Phototropism and gravitropism. AGC1-12 phosphorylates serine residues in the cytoplasmic loop of PIN-FORMED 1 (PIN1) and shares phosphosite preferences with D6PK. Our work strongly suggests that the D6PK family and AGC1-12 are critical components for both hypocotyl Phototropism and gravitropism, and that these kinases control tropic responses mainly through regulation of PIN-mediated auxin transport by protein phosphorylation.
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Asymmetric Auxin Distribution is Not Required to Establish Root Phototropism in Arabidopsis.
Plant & cell physiology, 2018Co-Authors: Taro Kimura, Ken Haga, Yasushi Shimizu-mitao, Yumiko Takebayashi, Hiroyuki Kasahara, Ken-ichiro Hayashi, Tatsuo Kakimoto, Tatsuya SakaiAbstract:An asymmetric auxin distribution pattern is assumed to underlie the tropic responses of seed plants. It is unclear, however, whether this pattern is required for root negative Phototropism. We here demonstrate that asymmetric auxin distribution is not required to establish root Phototropism in Arabidopsis. Our detailed analyses of auxin reporter genes indicate that auxin accumulates on the irradiated side of roots in response to an incidental gravitropic stimulus caused by phototropic bending. Further, an agravitropic mutant showed a suppression of this accumulation with an enhancement of the phototropic response. In this context, our pharmacological and genetic analyses revealed that both polar auxin transport and auxin biosynthesis are critical for the establishment of root gravitropism, but not for root Phototropism, and that defects in these processes actually enhance phototropic responses in roots. The auxin response factor double mutant arf7 arf19 and the auxin receptor mutant tir1 showed a slight reduction in phototropic curvatures in roots, suggesting that the transcriptional regulation by some specific ARF proteins and their regulators is at least partly involved in root Phototropism. However, the auxin antagonist PEO-IAA [α-(phenylethyl-2-one)-indole-3-acetic acid] suppressed root gravitropism and enhanced root Phototropism, suggesting that the TIR1/AFB auxin receptors and ARF transcriptional factors play minor roles in root Phototropism. Taken together, we conclude from our current data that the phototropic response in Arabidopsis roots is induced by an unknown mechanism that does not require asymmetric auxin distribution and that the Cholodny-Went hypothesis probably does not apply to root Phototropism.
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arabidopsis root Phototropism2 contributes to the adaptation to high intensity light in phototropic responses
The Plant Cell, 2015Co-Authors: Ken Haga, Tomoko Tsuchidamayama, Mizuki Yamada, Tatsuya SakaiAbstract:Living organisms adapt to changing light environments via mechanisms that enhance photosensitivity under darkness and attenuate photosensitivity under bright light conditions. In hypocotyl Phototropism, phototropin1 (phot1) blue light photoreceptors mediate both the pulse light-induced, first positive Phototropism and the continuous light-induced, second positive Phototropism, suggesting the existence of a mechanism that alters their photosensitivity. Here, we show that light induction of ROOT Phototropism2 (RPT2) underlies photosensory adaptation in hypocotyl Phototropism of Arabidopsis thaliana. rpt2 loss-of-function mutants exhibited increased photosensitivity to very low fluence blue light but were insensitive to low fluence blue light. Expression of RPT2 prior to phototropic stimulation in etiolated seedlings reduced photosensitivity during first positive Phototropism and accelerated second positive Phototropism. Our microscopy and biochemical analyses indicated that blue light irradiation causes dephosphorylation of NONPHOTOTROPIC HYPOCOTYL3 (NPH3) proteins and mediates their release from the plasma membrane. These phenomena correlate closely with the desensitization of phot1 signaling during the transition period from first positive Phototropism to second positive Phototropism. RPT2 modulated the phosphorylation of NPH3 and promoted reconstruction of the phot1-NPH3 complex on the plasma membrane. We conclude that photosensitivity is increased in the absence of RPT2 and that this results in the desensitization of phot1. Light-mediated induction of RPT2 then reduces the photosensitivity of phot1, which is required for second positive Phototropism under bright light conditions.
Christian Fankhauser - One of the best experts on this subject based on the ideXlab platform.
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Low Blue Light Enhances Phototropism by Releasing Cryptochrome1-Mediated Inhibition of PIF4 Expression.
Plant Physiology, 2020Co-Authors: Alessandra Boccaccini, Anupama Goyal, Elizabeth Karayekov, Martina Legris, Johanna Krahmer, Laure Allenbach-petrolati, Carlos Galvan-ampudia, Teva Vernoux, Jorge Casal, Christian FankhauserAbstract:Shade-avoiding plants, including Arabidopsis (Arabidopsis thaliana), display a number of growth responses, such as elongation of stem-like structures and repositioning of leaves, elicited by shade cues, including a reduction in the blue and red portions of the solar spectrum and a low-red to far-red ratio. Shade also promotes Phototropism of de-etiolated seedlings through repression of phytochrome B, presumably to enhance capture of unfiltered sunlight. Here we show that both low blue light and a low-red to far-red light ratio are required to rapidly enhance Phototropism in Arabidopsis seedlings. However, prolonged low blue light treatments are sufficient to promote Phototropism through reduced cryptochrome1 (cry1) activation. 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 quantitative DII-Venus, an auxin signaling reporter, indicates that low blue light leads to enhanced auxin signaling in the hypocotyl and, upon phototropic stimulation, a steeper auxin signaling 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.
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A phosphorylation switch turns a positive regulator of Phototropism into an inhibitor of the process.
Nature communications, 2018Co-Authors: Paolo Schumacher, Martine Trevisan, Emilie Demarsy, Patrice Waridel, Laure Allenbach Petrolati, Christian FankhauserAbstract:Phototropins are light-activated protein kinases, which contribute to photosynthesis optimization both through enhancement of photon absorption when light is limiting and avoidance responses in high light. This duality is in part endowed by the presence of phototropins with different photosensitivity (phot1 and phot2). Here we show that phot1, which senses low light to promote positive Phototropism (growth towards the light), also limits the response in high light. This response depends in part on phot1-mediated phosphorylation of Phytochrome Kinase Substrate 4 (PKS4). This light-regulated phosphorylation switch changes PKS4 from a Phototropism enhancer in low light to a factor limiting the process in high light. In such conditions phot1 and PKS4 phosphorylation prevent phototropic responses to shallow light gradients and limit Phototropism in a natural high light environment. Hence, by modifying PKS4 activity in high light the phot1-PKS4 regulon enables appropriate physiological adaptations over a range of light intensities.
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Shade Promotes Phototropism through Phytochrome B-Controlled Auxin Production.
Current biology : CB, 2016Co-Authors: Anupama Goyal, Jorge J. Casal, Elizabeth Karayekov, Vinicius Costa Galvão, Hong Ren, Christian FankhauserAbstract:Phototropism is an asymmetric growth response enabling plants to optimally position their organs. In flowering plants, the phototropin (phot) blue light receptors are essential to detect light gradients. In etiolated seedlings, the phototropic response is enhanced by the red/far-red (R/FR)-sensing phytochromes (phy) with a predominant function of phyA. In this study, we analyzed the influence of the phytochromes on Phototropism in green (de-etiolated) Arabidopsis seedlings. Our experiments in the laboratory and outdoors revealed that, in open environments (high R/FR ratio), phyB inhibits Phototropism. In contrast, under foliar shade, where access to direct sunlight becomes important, the phototropic response was strong. phyB modulates Phototropism, depending on the R/FR ratio, by controlling the activity of three basic-helix-loop-helix (bHLH) transcription factors of the PHYTOCHROME INTERACTING FACTORs (PIFs) family. Promotion of Phototropism depends on PIF-mediated induction of several members of the YUCCA gene family, leading to auxin production in the cotyledons. Our study identifies PIFs and YUCCAs as novel molecular players promoting Phototropism in photoautotrophic, but not etiolated, seedlings. Moreover, our findings reveal fundamental differences in the phytochrome-Phototropism crosstalk in etiolated versus green seedlings. We propose that in natural conditions where the light environment is not homogeneous, the uncovered phytochrome-phototropin co-action is important for plants to adapt their growth strategy to optimize photosynthetic light capture.
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repressor of ultraviolet b photomorphogenesis function allows efficient phototropin mediated ultraviolet b Phototropism in etiolated seedlings
Plant Science, 2016Co-Authors: Lucas Vanhaelewyn, Christian Fankhauser, Paolo Schumacher, Dirk Poelman, Dominique Van Der Straeten, Filip VandenbusscheAbstract:Ultraviolet B (UV-B) light is a part of the solar radiation which has significant effects on plant morphology, even at low doses. In Arabidopsis, many of these morphological changes have been attributed to a specific UV-B receptor, UV resistance locus 8 (UVR8). Recent findings showed that next to phototropin regulated Phototropism, UVR8 mediated signaling is able of inducing directional bending towards UV-B light in etiolated seedlings of Arabidopsis, in a phototropin independent manner. In this study, kinetic analysis of phototropic bending was used to evaluate the relative contribution of each of these pathways in UV-B mediated Phototropism. Diminishing UV-B light intensity favors the importance of phototropins. Molecular and genetic analyses suggest that UV-B is capable of inducing phototropin signaling relying on phototropin kinase activity and regulation of NPH3. Moreover, enhanced UVR8 responses in the UV-B hypersensitive rup1rup2 mutants interferes with the fast phototropin mediated Phototropism. Together the data suggest that phototropins are the most important receptors for UV-B induced Phototropism in etiolated seedlings, and a RUP mediated negative feedback pathway prevents UVR8 signaling to interfere with the phototropin dependent response.
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reduced Phototropism in pks mutants may be due to altered auxin regulated gene expression or reduced lateral auxin transport
Plant Journal, 2014Co-Authors: Chitose Kami, Kotaro T. Yamamoto, Claus Schwechheimer, Laure Allenbach, Melina Zourelidou, Karin Ljung, Frederic Schutz, Erika Isono, Masaaki K Watahiki, Christian FankhauserAbstract:Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers Phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated Phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on Phototropism is unknown; here we show that PKS proteins play a role at the interface between development and Phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.
Roger P. Hangarter - One of the best experts on this subject based on the ideXlab platform.
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the arabidopsis phytochrome kinase substrate2 protein is a phototropin signaling element that regulates leaf flattening and leaf positioning
Plant Physiology, 2010Co-Authors: Matthieu De Carbonnel, Patricia Lariguet, Isabelle Schepens, Roger P. Hangarter, Phillip A Davis, Rob M G Roelfsema, Shinichiro Inoue, Markus Geisler, Kenichiro Shimazaki, Christian FankhauserAbstract:In Arabidopsis (Arabidopsis thaliana), the blue light photoreceptor phototropins (phot1 and phot2) fine-tune the photosynthetic status of the plant by controlling several important adaptive processes in response to environmental light variations. These processes include stem and petiole Phototropism (leaf positioning), leaf flattening, stomatal opening, and chloroplast movements. The PHYTOCHROME KINASE SUBSTRATE (PKS) protein family comprises four members in Arabidopsis (PKS1-PKS4). PKS1 is a novel phot1 signaling element during Phototropism, as it interacts with phot1 and the important signaling element NONPHOTOTROPIC HYPOCOTYL3 (NPH3) and is required for normal phot1-mediated Phototropism. In this study, we have analyzed more globally the role of three PKS members (PKS1, PKS2, and PKS4). Systematic analysis of mutants reveals that PKS2 (and to a lesser extent PKS1) act in the same subset of phototropin-controlled responses as NPH3, namely leaf flattening and positioning. PKS1, PKS2, and NPH3 coimmunoprecipitate with both phot1-green fluorescent protein and phot2-green fluorescent protein in leaf extracts. Genetic experiments position PKS2 within phot1 and phot2 pathways controlling leaf positioning and leaf flattening, respectively. NPH3 can act in both phot1 and phot2 pathways, and synergistic interactions observed between pks2 and nph3 mutants suggest complementary roles of PKS2 and NPH3 during phototropin signaling. Finally, several observations further suggest that PKS2 may regulate leaf flattening and positioning by controlling auxin homeostasis. Together with previous findings, our results indicate that the PKS proteins represent an important family of phototropin signaling proteins.
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Phototropism bending towards enlightenment
The Plant Cell, 2006Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:Research on Phototropism has had far-reaching consequences in the field of plant biology, from helping to refute the ancient misconception of plant insensitivity to the environment to the discovery of the plant hormone auxin and the identification of the phototropin photoreceptors. In this essay, we
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a brassinosteroid hypersensitive mutant of bak1 indicates that a convergence of photomorphogenic and hormonal signaling modulates Phototropism
Plant Physiology, 2005Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:The phototropic response of Arabidopsis (Arabidopsis thaliana) is induced by the phototropin photoreceptors and modulated by the cryptochrome and phytochrome photoreceptors. Downstream of these photoreceptors, asymmetric lateral redistribution of auxin underlies the differential growth, which results in Phototropism. Historical physiological evidence and recent analysis of hormone-induced gene expression demonstrate that auxin and brassinosteroid signaling function interdependently. Similarly, in this study we report evidence that interactions between brassinosteroids and auxin signaling modulate phototropic responsiveness. We found that elongated, a previously identified photomorphogenesis mutant, enhances high-light Phototropism and represents a unique allele of BAK1/SERK3, a receptor kinase implicated in brassinosteroid perception. Altogether, our results support the hypothesis that phototropic responsiveness is modulated by inputs that influence control of auxin response factor-mediated transcription.
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phytochrome modulation of blue light induced Phototropism
Plant Cell and Environment, 2004Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:Red light enhances hypocotyl Phototropism toward unilateral blue light through a phytochrome-mediated response. This study demonstrates how the phytochromes modulate blue-light-induced Phototropism in the absence of a red light pre-treatment. It was found that phytochromes A, B, and D have conditionally overlapping functions in the promotion of blue-light-induced Phototropism. Under very low blue light intensities (0.01 µmol m−2 s−1) phyA activity is necessary for the progression of a normal phototropic response, whereas above 1.0 µmol m−1 s−2 phyB and phyD have functional redundancy with phyA to promote Phototropism. PhyA also contributes to attenuation of Phototropism under high fluence rates of unilateral blue light, which was previously shown to be dependent on the phototropins and cryptochromes. From these results, it appears that phytochromes are required to develop a robust phototropic response under low fluence rates, whereas under high irradiances where Phototropism may be less important, phyA suppresses Phototropism.
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second positive Phototropism results from coordinated co action of the phototropins and cryptochromes
Plant Physiology, 2003Co-Authors: Craig W Whippo, Roger P. HangarterAbstract:Phototropism and hypocotyl growth inhibition are modulated by the coaction of different blue-light photoreceptors and their signaling pathways. How seedlings integrate the activities of the different blue-light photoreceptors to coordinate these hypocotyl growth responses is still unclear. We have used time-lapse imaging and a nontraditional mathematical approach to conduct a detailed examination of Phototropism in wild-type Arabidopsis and various blue-light photoreceptor mutants. Our results indicate that high fluence rates of blue light (100 μmol m – 2 s – 1 ) attenuate Phototropism through the coaction of the phototropin and cryptochrome blue-light photoreceptors. In contrast, we also demonstrate that phototropins and cryptochromes function together to enhance Phototropism under low fluence rates ( – 2 s – 1 ) of blue light. Based on our results, we hypothesize that phototropins and cryptochromes regulate Phototropism by coordinating the balance between stimulation and inhibition of growth of the hypocotyl depending on the fluence rate of blue light.
Ken Haga - One of the best experts on this subject based on the ideXlab platform.
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Physiological Characterization of Phototropism in Arabidopsis Seedlings.
Methods in molecular biology (Clifton N.J.), 2019Co-Authors: Ken Haga, Taro KimuraAbstract:To date, many mutants have been isolated from dicot plants, including Arabidopsis thaliana, and the physiological roles of the isolated genes have been identified. Molecular genetic analyses have usually been conducted in the model plant Arabidopsis to identify blue-light photoreceptors and key signaling components in phototropic responses. Despite these investigations, several molecular mechanisms involved in Phototropism remain unknown, possibly because detailed physiological analyses have not been conducted properly in the isolated mutants. This chapter describes an approach for the detailed investigation of hypocotyl and root Phototropism in Arabidopsis seedlings. The information provided here is expected to facilitate the analysis of phototropic responses in other plant species.
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Roles of AGCVIII Kinases in the Hypocotyl Phototropism of Arabidopsis Seedlings.
Plant & cell physiology, 2018Co-Authors: Ken Haga, Taro Kimura, Lena Frank, Claus Schwechheimer, Tatsuya SakaiAbstract:Regulation of protein function by phosphorylation and dephosphorylation is an important mechanism in many cellular events. The phototropin blue-light photoreceptors, plant-specific AGCVIII kinases, are essential for phototropic responses. Members of the D6 PROTEIN KINASE (D6PK) family, representing a subfamily of the AGCVIII kinases, also contribute to phototropic responses, suggesting that possibly further AGCVIII kinases may potentially control Phototropism. The present study investigates the functional roles of Arabidopsis (Arabidopsis thaliana) AGCVIII kinases in hypocotyl Phototropism. We demonstrate that D6PK family kinases are not only required for the second but also for the first positive Phototropism. In addition, we find that a previously uncharacterized AGCVIII protein, AGC1-12, is involved in the first positive Phototropism and gravitropism. AGC1-12 phosphorylates serine residues in the cytoplasmic loop of PIN-FORMED 1 (PIN1) and shares phosphosite preferences with D6PK. Our work strongly suggests that the D6PK family and AGC1-12 are critical components for both hypocotyl Phototropism and gravitropism, and that these kinases control tropic responses mainly through regulation of PIN-mediated auxin transport by protein phosphorylation.
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Asymmetric Auxin Distribution is Not Required to Establish Root Phototropism in Arabidopsis.
Plant & cell physiology, 2018Co-Authors: Taro Kimura, Ken Haga, Yasushi Shimizu-mitao, Yumiko Takebayashi, Hiroyuki Kasahara, Ken-ichiro Hayashi, Tatsuo Kakimoto, Tatsuya SakaiAbstract:An asymmetric auxin distribution pattern is assumed to underlie the tropic responses of seed plants. It is unclear, however, whether this pattern is required for root negative Phototropism. We here demonstrate that asymmetric auxin distribution is not required to establish root Phototropism in Arabidopsis. Our detailed analyses of auxin reporter genes indicate that auxin accumulates on the irradiated side of roots in response to an incidental gravitropic stimulus caused by phototropic bending. Further, an agravitropic mutant showed a suppression of this accumulation with an enhancement of the phototropic response. In this context, our pharmacological and genetic analyses revealed that both polar auxin transport and auxin biosynthesis are critical for the establishment of root gravitropism, but not for root Phototropism, and that defects in these processes actually enhance phototropic responses in roots. The auxin response factor double mutant arf7 arf19 and the auxin receptor mutant tir1 showed a slight reduction in phototropic curvatures in roots, suggesting that the transcriptional regulation by some specific ARF proteins and their regulators is at least partly involved in root Phototropism. However, the auxin antagonist PEO-IAA [α-(phenylethyl-2-one)-indole-3-acetic acid] suppressed root gravitropism and enhanced root Phototropism, suggesting that the TIR1/AFB auxin receptors and ARF transcriptional factors play minor roles in root Phototropism. Taken together, we conclude from our current data that the phototropic response in Arabidopsis roots is induced by an unknown mechanism that does not require asymmetric auxin distribution and that the Cholodny-Went hypothesis probably does not apply to root Phototropism.
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arabidopsis root Phototropism2 contributes to the adaptation to high intensity light in phototropic responses
The Plant Cell, 2015Co-Authors: Ken Haga, Tomoko Tsuchidamayama, Mizuki Yamada, Tatsuya SakaiAbstract:Living organisms adapt to changing light environments via mechanisms that enhance photosensitivity under darkness and attenuate photosensitivity under bright light conditions. In hypocotyl Phototropism, phototropin1 (phot1) blue light photoreceptors mediate both the pulse light-induced, first positive Phototropism and the continuous light-induced, second positive Phototropism, suggesting the existence of a mechanism that alters their photosensitivity. Here, we show that light induction of ROOT Phototropism2 (RPT2) underlies photosensory adaptation in hypocotyl Phototropism of Arabidopsis thaliana. rpt2 loss-of-function mutants exhibited increased photosensitivity to very low fluence blue light but were insensitive to low fluence blue light. Expression of RPT2 prior to phototropic stimulation in etiolated seedlings reduced photosensitivity during first positive Phototropism and accelerated second positive Phototropism. Our microscopy and biochemical analyses indicated that blue light irradiation causes dephosphorylation of NONPHOTOTROPIC HYPOCOTYL3 (NPH3) proteins and mediates their release from the plasma membrane. These phenomena correlate closely with the desensitization of phot1 signaling during the transition period from first positive Phototropism to second positive Phototropism. RPT2 modulated the phosphorylation of NPH3 and promoted reconstruction of the phot1-NPH3 complex on the plasma membrane. We conclude that photosensitivity is increased in the absence of RPT2 and that this results in the desensitization of phot1. Light-mediated induction of RPT2 then reduces the photosensitivity of phot1, which is required for second positive Phototropism under bright light conditions.
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PINOID AGC Kinases are Necessary for Phytochrome-Mediated Enhancement of Hypocotyl Phototropism in Arabidopsis
Plant physiology, 2014Co-Authors: Ken Haga, Ken-ichiro Hayashi, Tatsuya SakaiAbstract:Several members of the AGCVIII kinase subfamily, which includes PINOID (PID), PID2, and WAVY ROOT GROWTH (WAG) proteins, have previously been shown to phosphorylate PIN-FORMED (PIN) auxin transporters and control the auxin flow in plants. PID has been proposed as a key component of the phototropin signaling pathway that induces phototropic responses, although the responses were not significantly impaired in the pid single and pid wag1 wag2 triple mutants. This raises questions about the functional roles of the PID family in phototropic responses. Here, we investigated hypocotyl Phototropism in the pid pid2 wag1 wag2 quadruple mutant in detail to clarify the roles of the PID family in Arabidopsis (Arabidopsis thaliana). The pid quadruple mutants exhibited moderate responses in continuous light-induced Phototropism with a decrease in growth rates of hypocotyls and normal responses in pulse-induced Phototropism. However, they showed serious defects in enhancements of pulse-induced phototropic curvatures and lateral fluorescent auxin transport by red light pretreatment. Red light pretreatment significantly reduced the expression level of PID, and the constitutive expression of PID prevented pulse-induced Phototropism, irrespective of red light pretreatment. This suggests that the PID family plays a significant role in phytochrome-mediated phototropic enhancement but not the phototropin signaling pathway. Red light treatment enhanced the intracellular accumulation of PIN proteins in response to the vesicle-trafficking inhibitor brefeldin A in addition to increasing their expression levels. Taken together, these results suggest that red light preirradiation enhances phototropic curvatures by up-regulation of PIN proteins, which are not being phosphorylated by the PID family.
Kotaro T. Yamamoto - One of the best experts on this subject based on the ideXlab platform.
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Phototropism in gametophytic shoots of the moss Physcomitrella patens.
Plant signaling & behavior, 2015Co-Authors: Liang Bao, Kotaro T. Yamamoto, Tomomichi FujitaAbstract:Shoot Phototropism enables plants to position their photosynthetic organs in favorable light conditions and thus benefits growth and metabolism in land plants. To understand the evolution of this response, we established an experimental system to study Phototropism in gametophores of the moss Physcomitrella patens. The phototropic response of gametophores occurs slowly; a clear response takes place more than 24 hours after the onset of unilateral light irradiation, likely due to the slow growth rate of gametophores. We also found that red and far-red light can induce Phototropism, with blue light being less effective. These results suggest that plants used a broad range of light wavelengths as phototropic signals during the early evolution of land plants.
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negative Phototropism is seen in arabidopsis inflorescences when auxin signaling is reduced to a minimal level by an aux iaa dominant mutation axr2
Plant Signaling & Behavior, 2015Co-Authors: Atsuko Sato, Shu Sasaki, Jun Matsuzaki, Kotaro T. YamamotoAbstract:Inflorescences of a dominant mutant of Arabidopsis Aux/IAA7, axr2, showed negative Phototropism with a similar fluence response curve to the positive Phototropism of wild-type stems. Application of a synthetic auxin, NAA, and an inhibitor of polar auxin transport, NPA, increased and decreased respectively the magnitude of the phototropic response in the wild type, while in axr2 application of NAA reduced the negative phototropic response and NPA had no effect. Decapitation of the apex induced a small negative Phototropism in wild-type stems, and had no effect in axr2 plants. Inflorescences of the double mutants of auxin transporters, pgp1 pgp19, showed no phototropic response, while decapitation resulted in a negative phototropic response. These results suggest that negative Phototropism can occur when the level of auxin or of auxin signaling is reduced to a minimal level, and that in plant axial organs the default phototropic response to unilateral blue light may be negative. Expression of axr2 protein by an endodermis-specific promoter resulted in agravitropism of inflorescences in a similar way to that of axr2, but Phototropism was normal, confirming that the endodermis does not play a critical role in Phototropism.
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negative Phototropism is seen in arabidopsis inflorescences when auxin signaling is reduced to a minimal level by an aux iaa dominant mutation axr2
Plant Signaling & Behavior, 2015Co-Authors: Atsuko Sato, Shu Sasaki, Jun Matsuzaki, Kotaro T. YamamotoAbstract:Inflorescences of a dominant mutant of Arabidopsis Aux/IAA7, axr2, showed negative Phototropism with a similar fluence response curve to the positive Phototropism of wild-type stems. Application of a synthetic auxin, NAA, and an inhibitor of polar auxin transport, NPA, increased and decreased respectively the magnitude of the phototropic response in the wild type, while in axr2 application of NAA reduced the negative phototropic response and NPA had no effect. Decapitation of the apex induced a small negative Phototropism in wild-type stems, and had no effect in axr2 plants. Inflorescences of the double mutants of auxin transporters, pgp1 pgp19, showed no phototropic response, while decapitation resulted in a negative phototropic response. These results suggest that negative Phototropism can occur when the level of auxin or of auxin signaling is reduced to a minimal level, and that in plant axial organs the default phototropic response to unilateral blue light may be negative. Expression of axr2 protein b...
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light dependent gravitropism and negative Phototropism of inflorescence stems in a dominant aux iaa mutant of arabidopsis thaliana axr2
Journal of Plant Research, 2014Co-Authors: Atsuko Sato, Shu Sasaki, Jun Matsuzaki, Kotaro T. YamamotoAbstract:Gravitropism and Phototropism of the primary inflorescence stems were examined in a dominant Aux/IAA mutant of Arabidopsis, axr2/iaa7, which did not display either tropism in hypocotyls. axr2-1 stems completely lacked gravitropism in the dark but slowly regained it in light condition. Though wild-type stems showed positive Phototropism, axr2 stems displayed negative Phototropism with essentially the same light fluence-response curve as the wild type (WT). Application of 1-naphthaleneacetic acid-containing lanolin to the stem tips enhanced the positive Phototropism of WT, and reduced the negative Phototropism of axr2. Decapitation of stems caused a small negative Phototropism in WT, but did not affect the negative Phototropism of axr2. p-glycoprotein 1 (pgp1) pgp19 double mutants showed no Phototropism, while decapitated double mutants exhibited negative Phototropism. Expression of auxin-responsive IAA14/SLR, IAA19/MSG2 and SAUR50 genes was reduced in axr2 and pgp1 pgp19 stems relative to that of WT. These suggest that the phototropic response of stem is proportional to the auxin supply from the shoot apex, and that negative Phototropism may be a basal response to unilateral blue-light irradiation when the levels of auxin or auxin signaling are reduced to the minimal level in the primary stems. In contrast, all of these treatments reduced or did not affect gravitropism in wild-type or axr2 stems. Tropic responses of the transgenic lines that expressed axr2-1 protein by the endodermis-specific promoter suggest that AXR2-dependent auxin response in the endodermis plays a more crucial role in gravitropism than in Phototropism in stems but no significant roles in either tropism in hypocotyls.
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reduced Phototropism in pks mutants may be due to altered auxin regulated gene expression or reduced lateral auxin transport
Plant Journal, 2014Co-Authors: Chitose Kami, Kotaro T. Yamamoto, Claus Schwechheimer, Laure Allenbach, Melina Zourelidou, Karin Ljung, Frederic Schutz, Erika Isono, Masaaki K Watahiki, Christian FankhauserAbstract:Phototropism allows plants to orient their photosynthetic organs towards the light. In Arabidopsis, phototropins 1 and 2 sense directional blue light such that phot1 triggers Phototropism in response to low fluence rates, while both phot1 and phot2 mediate this response under higher light conditions. Phototropism results from asymmetric growth in the hypocotyl elongation zone that depends on an auxin gradient across the embryonic stem. How phototropin activation leads to this growth response is still poorly understood. Members of the phytochrome kinase substrate (PKS) family may act early in this pathway, because PKS1, PKS2 and PKS4 are needed for a normal phototropic response and they associate with phot1 in vivo. Here we show that PKS proteins are needed both for phot1- and phot2-mediated Phototropism. The phototropic response is conditioned by the developmental asymmetry of dicotyledonous seedlings, such that there is a faster growth reorientation when cotyledons face away from the light compared with seedlings whose cotyledons face the light. The molecular basis for this developmental effect on Phototropism is unknown; here we show that PKS proteins play a role at the interface between development and Phototropism. Moreover, we present evidence for a role of PKS genes in hypocotyl gravi-reorientation that is independent of photoreceptors. pks mutants have normal levels of auxin and normal polar auxin transport, however they show altered expression patterns of auxin marker genes. This situation suggests that PKS proteins are involved in auxin signaling and/or lateral auxin redistribution.