Light signaling

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    HY5 regulates light-responsive transcription of microRNA163 to promote primary root elongation in Arabidopsis seedlings
    Tao Li, Hongmei Lian, Haojie Li, Yufang Xu and Huiyong Zhang
    J Integr Plant Biol 2021, 63 (8): 1437-1450.  
    doi: 10.1111/jipb.13099
    Abstract (Browse 365)  |   Save
    MicroRNAs (miRNAs) play key roles in the post-transcriptional regulation of gene expression in plants. Many miRNAs are responsive to environmental signals. Light is the first environmental signal perceived by plants after emergence from the soil. However, less is known about the roles and regulatory mechanism of miRNAs in response to light signal. Here, using small RNA sequencing, we determined that miR163 is significantly rapidly induced by light signaling in Arabidopsis thaliana seedlings. The light-inducible response of miR163 functions genetically downstream of LONG HYPOCOTYL 5 (HY5), a central positive regulator of photomorphogenesis. HY5 directly binds to the two G/C-hybrid elements in the miR163 promoter with unequal affinity; one of these elements, which is located next to the transcription start site, plays a major role in light-induced expression of miR163. Overexpression of miR163 rescued the defective primary root elongation of hy5 seedlings without affecting lateral root growth, whereas overexpressing of miR163 target PXMT1 inhibited primary root elongation. These findings provide insight into understanding the post-transcriptional regulation of root photomorphogenesis mediated by the HY5-miR163-PXMT1 network.
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    Phytochrome B interacts with SWC6 and ARP6 to regulate H2A.Z deposition and photomorphogensis in Arabidopsis
    Xuxu Wei, Wanting Wang, Peng Xu, Wenxiu Wang, Tongtong Guo, Shuang Kou, Minqing Liu, Yake Niu, Hong‐Quan Yang and Zhilei Mao
    J Integr Plant Biol 2021, 63 (6): 1133-1146.  
    DOI: 10.1111/jipb.13111
    Abstract (Browse 272)  |   Save
    Light serves as a crucial environmental cue which modulates plant growth and development, and which is controlled by multiple photoreceptors including the primary red light photoreceptor, phytochrome B (phyB). The signaling mechanism of phyB involves direct interactions with a group of basic helix-loop-helix (bHLH) transcription factors, PHYTOCHROME-INTERACTING FACTORS (PIFs), and the negative regulators of photomorphogenesis, COP1 and SPAs. H2A.Z is an evolutionarily conserved H2A variant which plays essential roles in transcriptional regulation. The replacement of H2A with H2A.Z is catalyzed by the SWR1 complex. Here, we show that the Pfr form of phyB physically interacts with the SWR1 complex subunits SWC6 and ARP6. phyB and ARP6 co-regulate numerous genes in the same direction, some of which are associated with auxin biosynthesis and response including YUC9, which encodes a rate-limiting enzyme in the tryptophan-dependent auxin biosynthesis pathway. Moreover, phyB and HY5/HYH act to inhibit hypocotyl elongation partially through repression of auxin biosynthesis. Based on our findings and previous studies, we propose that phyB promotes H2A.Z deposition at YUC9 to inhibit its expression through direct phyB-SWC6/ARP6 interactions, leading to repression of auxin biosynthesis, and thus inhibition of hypocotyl elongation in red light.
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    Regulation of cytoskeleton‐associated protein activities: Linking cellular signals to plant cytoskeletal function
    Na Lian, Xinwei Wang, Yanping Jing and Jinxing Lin
    J Integr Plant Biol 2021, 63 (1): 241-250.  
    doi: 10.1111/jipb.13046
    Abstract (Browse 289)  |   Save
    The plant cytoskeleton undergoes dynamic remodeling in response to diverse developmental and environmental cues. Remodeling of the cytoskeleton coordinates growth in plant cells, including trafficking and exocytosis of membrane and wall components during cell expansion, and regulation of hypocotyl elongation in response to light. Cytoskeletal remodeling also has key functions in disease resistance and abiotic stress responses. Many stimuli result in altered activity of cytoskeleton‐associated proteins, microtubule‐associated proteins (MAPs) and actin‐binding proteins (ABPs). MAPs and ABPs are the main players determining the spatiotemporally dynamic nature of the cytoskeleton, functioning in a sensory hub that decodes signals to modulate plant cytoskeletal behavior. Moreover, MAP and ABP activities and levels are precisely regulated during development and environmental responses, but our understanding of this process remains limited. In this review, we summarize the evidence linking multiple signaling pathways, MAP and ABP activities and levels, and cytoskeletal rearrangements in plant cells. We highlight advances in elucidating the multiple mechanisms that regulate MAP and ABP activities and levels, including calcium and calmodulin signaling, ROP GTPase activity, phospholipid signaling, and post‐translational modifications.
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    The C-terminal 17 amino acids of the photoreceptor UVR8 is involved in the fine-tuning of UV-B signaling
    Li Lin, Huaxi Dong, Guoqian Yang and Ruohe Yin
    J Integr Plant Biol 2020, 62 (9): 1327-1340.  
    doi: 10.1111/jipb.12977
    Abstract (Browse 443)  |   Save

    Plant UV‐B responses are mediated by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8). In response to UV‐B irradiation, UVR8 homodimers dissociate into monomers that bind to the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1). The interaction of the C27 domain in the C‐terminal tail of UVR8 with the WD40 domain of COP1 is critical for UV‐B signaling. However, the function of the last 17 amino acids (C17) of the C‐terminus of UVR8, which are adjacent to C27, is unknown, although they are largely conserved in land plants. In this study, we established that Arabidopsis thaliana UVR8 C17 binds to full‐length UVR8, but not to COP1, and reduces COP1 binding to the remaining portion of UVR8, including C27. We hypothesized that overexpression of C17 in a wild‐type background would have a dominant negative effect on UVR8 activity; however, C17 overexpression caused strong silencing of endogenous UVR8 , precluding a detailed analysis. We therefore generated YFP‐UVR8N423 transgenic lines, in which C17 was deleted, to examine C17 function indirectly. YFP‐UVR8N423 was more active than YFP‐UVR8, suggesting that C17 inhibits UV‐B signaling by attenuating binding between C27 and COP1. Our study reveals an inhibitory role for UVR8 C17 in fine‐tuning UVR8–COP1 interactions during UV‐B signaling.

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    Photobiology: Light signal transduction and photomorphogenesis
    Hongtao Liu, Rongcheng Lin and Xing Wang Deng
    J Integr Plant Biol 2020, 62 (9): 1267-1269.  
    doi: 10.1111/jipb.13004
    Abstract (Browse 844)  |   Save

    Light is crucial for plants, not only because of photosynthesis, but also because of photomorphogenesis. As one of the most important environmental cues, light influences multiple responses in plants, including seed germination, seedling de‐etiolation, shade avoidance, phototropism, stomata and chloroplast movement, circadian rhythms, and flowering time. In model plant Arabidopsis thaliana, at least five types of photoreceptors are involved in the regulation of overlapping physiological functions essential to plant growth and development. The main photoreceptors include the UV‐B photoreceptor UV RESISTANCE LOCUS 8 (UVR8) (Rizzini et al. 2011), the blue light photoreceptors, known as cryptochromes (CRYs) (Lin 2002); the blue light/UV‐A photoreceptor phototropins (PHOTs) (Briggs and Christie 2002); the LOV‐domain/F‐box proteins ZEITLUPE (ZTL), FLAVIN BINDING, KELCH REPEAT, F‐BOX PROTEIN 1 (FKF), and LOV KELCH PROTEIN2 (LKP2) (Demarsy and Fankhauser 2009); and the red/far‐red light photoreceptors, called phytochromes (PHYs) (Quail 2002). How those photoreceptors transduce respective light signals are fundamental questions in plant biology.

    In this Special Issue, we collected three reviews to summarize the recent progress in light signaling and five articles to show the latest research progress in photobiology from different perspectives and raise exciting new questions for future investigations.

    The review by Yadav et al. (2020) summarized the current developments in light signaling with a major focus on UV‐B‐mediated plant growth regulation. They outlined the perception of far‐red, red, blue, and UV‐B signals and the central regulatory intermediates involved in their downstream signaling pathways. It further focuses on current understanding of the developmental changes shown by plants in response to UV‐B radiation. It also discusses the diverse strategies plants have adapted at molecular, biochemical, and metabolic levels to protect themselves from UV‐B mediated damages.

    Transcription regulation is critical for light signaling. B‐box proteins are a class of zinc‐coordinated transcription factors or regulators that not only directly mediate the transcription of target genes, but also interact with various other factors to create a complex regulatory network involved in the precise control of plant growth and development. A group of B‐box proteins (BBXs) function as important players in light‐mediated developmental processes. Song et al. (2020) summarized and highlighted the recent findings concerning the critical regulatory functions of BBXs in photoperiodic flowering, light signal transduction and light‐induced pigment accumulation and their molecular modes of action at the transcriptional and post‐translational levels in plants.

    Seed dormancy is an evolved trait that determines the timing of germination, thereby playing essential roles in ensuring plant survival and agricultural production. Seed dormancy and the subsequent germination are controlled by both the internal cues, mainly hormones and several dormancy proteins, and the environmental signals, including light. Yang et al. (2020b) provided an overview of the molecular mechanism by which seed light signal modulates the induction, maintenance and release of seed dormancy, as well as seed germination, and further summarize/discuss the interaction between light and the internal hormones and dormancy‐specific regulators.

    CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) is a RING finger E3 ubiquitin ligase that acts downstream of the PHYs, CRYs, and UVR8 (Ang and Deng 1994Christie et al. 2012). In response to UV‐B irradiation, UVR8 homodimers dissociate into monomers that bind to the E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1). The interaction of the C27 domain in the C‐terminal tail of UVR8 with the WD40 domain of COP1 is critical for UV‐B signaling. Lin et al. (2020) report an inhibitory role for UVR8 C17 in fine‐tuning UVR8–COP1 interactions during U2020V‐B signaling. They established that Arabidopsis UVR8 C17 binds to full‐length UVR8, but not to COP1, and reduces COP1 binding to the remaining portion of UVR8, including C27.

    Being shaded is a common environmental stress for plants, especially for densely planted crops. Shaded plants display shade avoidance syndrome (SAS): elongated hypocotyls, internodes, and petioles, hyponastic leaves, early flowering and are inhibited in branching. Shade decreases red: far‐red (R:FR) ratios that inactivate phytochrome B (PHYB) and subsequently release phytochrome interaction factors (PIFs). ZTL is a blue light photoreceptor and circadian clock component, which is also involved in floral rhythms and plant defense in Nicotiana attenuata. Zou et al. (2019) show that ZTL may regulate PHYB‐ and the auxin‐mediated signaling pathway, which functions in the SAS of N. attenuata.

    Light regulates the distribution pattern of chloroplasts in photosynthesizing plant cells (Wada et al. 2003). Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic interactions. In leaf palisade cells of Arabidopsis, mitochondria exhibit blue‐light‐dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue‐light receptor phototropins. Islam et al. (2020) further demonstrate that the physical interaction between mitochondria and chloroplasts is cooperatively mediated by phototropin 2‐ and photosynthesis‐dependent signals.

    The phyB photoreceptor plays a major role that inputs light signals to regulate seed dormancy and germination. PIF1 is a key transcription factor repressing phyB‐mediated seed germination, while REVEILLE1 (RVE1) factor functions as a curial regulator in controlling both seed dormancy and germination. Yang et al. (2020a) found that PIF1 physically interacts with RVE1. They formed a transcriptional feedback loop that coordinately inhibits seed germination, providing a mechanistic understanding of how phyB‐mediated light signal is transduced to the seeds.

    The transition to flowering is the most dramatic phase change in flowering plants and is crucial for reproductive success. Plants integrate environmental cues with endogenous signals to regulate flowering time. The amount of FLOWERING LOCUS T (FT), which encodes a mobile stimulus largely determines the flowering time. Liu et al. (2020) demonstrate that ambient temperatures regulate both FT messenger RNA expression and FT protein trafficking to prevent precocious flowering at low temperatures and ensure plant reproductive success under favorable environmental conditions.

    This Special Issue covers a selected range of topics and directions in photobiology. In recent years, significant progress has been made in plant photobiology research, from the understanding of light signal transduction, to novel functions of photoreceptors. Knowledge gained from these studies will be important not only to the understanding of light signal transduction, but also to agricultural efforts for better crop yield and performance.

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    Induction of γ-aminobutyric acid plays a positive role to Arabidopsis resistance against Pseudomonas syringae
    Xiangxiong Deng, Xuwen Xu, Yu Liu, Yan Zhang, Liuyi Yang, Shuqun Zhang and Juan Xu
    J Integr Plant Biol 2020, 62 (11): 1797-1812.  
    doi: 10.1111/jipb.12974
    Abstract (Browse 369)  |   Save

    Gamma‐aminobutyric acid (GABA) is an important metabolite which functions in plant growth, development, and stress responses. However, its role in plant defense and how it is regulated are largely unknown. Here, we report a detailed analysis of GABA induction during the resistance response to Pseudomonas syringae in Arabidopsis thaliana. While searching for the mechanism underlying the pathogen‐responsive mitogen‐activated protein kinase (MPK)3/MPK6 signaling cascade in plant immunity, we found that activation of MPK3/MPK6 greatly induced GABA biosynthesis, which is dependent on the glutamate decarboxylase genes GAD1 and GAD4. Inoculation with Pseudomonas syringae pv tomato DC3000 (Pst) and Pst‐avrRpt2 expressing the avrRpt2 effector gene induced GAD1 and GAD4 gene expression and increased the levels of GABA. Genetic evidence revealed that GAD1, GAD2, and GAD4 play important roles in both GABA biosynthesis and plant resistance in response to Pst‐avrRpt2 infection. The gad1/2/4 triple and gad1/2/4/5 quadruple mutants, in which the GABA levels were extremely low, were more susceptible to both Pst and Pst‐avrRpt2. Functional loss of MPK3/MPK6, or their upstream MKK4/MKK5, or their downstream substrate WRKY33 suppressed the induction of GAD1 and GAD4 expression after Pst‐avrRpt2 treatment. Our findings shed light on both the regulation and role of GABA in the plant immunity to a bacterial pathogen.

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    FKF1 F-box protein promotes flowering in part by negatively regulating DELLA protein stability under long-day photoperiod in Arabidopsis
    Jindong Yan, Xinmei Li, Bingjie Zeng, Ming Zhong, Jiaxin Yang, Piao Yang, Xin Li, Chongsheng He, Jianzhong Lin, Xuanming Liu and Xiaoying Zhao
    J Integr Plant Biol 2020, 62 (11): 1717-1740.  
    doi: 10.1111/jipb.12971
    Abstract (Browse 408)  |   Save

    FLAVIN‐BINDING KELCH REPEAT F‐BOX 1 (FKF1) encodes an F‐box protein that regulates photoperiod flowering in Arabidopsis under long‐day conditions (LDs). Gibberellin (GA) is also important for regulating flowering under LDs. However, how FKF1 and the GA pathway work in concert in regulating flowering is not fully understood. Here, we showed that the mutation of FKF1 could cause accumulation of DELLA proteins, which are crucial repressors in GA signaling pathway, thereby reducing plant sensitivity to GA in flowering. Both in vitro and in vivo biochemical analyses demonstrated that FKF1 directly interacted with DELLA proteins. Furthermore, we showed that FKF1 promoted ubiquitination and degradation of DELLA proteins. Analysis of genetic data revealed that FKF1 acted partially through DELLAs to regulate flowering under LDs. In addition, DELLAs exerted a negative feedback on FKF1 expression. Collectively, these findings demonstrate that FKF1 promotes flowering partially by negatively regulating DELLA protein stability under LDs, and suggesting a potential mechanism linking the FKF1 to the GA signaling DELLA proteins.

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    PIF1 and RVE1 form a transcriptional feedback loop to control light-mediated seed germination in Arabidopsis
    Liwen Yang, Zhimin Jiang, Yanjun Jing and Rongcheng Lin
    J Integr Plant Biol 2020, 62 (9): 1372-1384.  
    doi: 10.1111/jipb.12938
    Abstract (Browse 384)  |   Save

    The phytochrome B (phyB) photoreceptor plays a major role that inputs light signals to regulate seed dormancy and germination. PHYTOCHROME‐INTERACTING FACTOR1 (PIF1) is a key transcription factor repressing phyB‐mediated seed germination, while REVEILLE1 (RVE1) factor functions as a curial regulator in controlling both seed dormancy and germination. However, the relationship between the PIF1‐ and RVE1‐modulated signaling pathways remains mostly unknown. Here, we find that PIF1 physically interacts with RVE1. Genetic analysis indicates that RVE1 inhibition on seed germination requires PIF1; reciprocally, the repressive effect of PIF1 is partially dependent on RVE1. Strikingly, PIF1 and RVE1 directly bind to the promoter and activate the expression of each other. Furthermore, PIF1 and RVE1 coordinately regulate the transcription of many downstream genes involved in abscisic acid and gibberellin pathways. Moreover, PIF1 enhances the DNA‐binding ability and transcriptional repression activity of RVE1 in regulating GIBBERELLIN 3‐OXIDASE2, and RVE1 promotes PIF1's DNA‐binding ability in modulating ABSCISIC ACID‐INSENSITIVE3 expression. Thus, this study demonstrates that PIF1 and RVE1 form a transcriptional feedback loop that coordinately inhibits seed germination, providing a mechanistic understanding of how phyB‐mediated light signal is transduced to the seeds.

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    B-box proteins: Pivotal players in light-mediated development in plants
    Zhaoqing Song, Yeting Bian, Jiujie Liu, Yuting Sun and Dongqing Xu
    J Integr Plant Biol 2020, 62 (9): 1293-1309.  
    doi: 10.1111/jipb.12935
    Abstract (Browse 385)  |   Save

    Light signals mediate a number of physiological and developmental processes in plants, such as flowering, photomorphogenesis, and pigment accumulation. Emerging evidence has revealed that a group of B‐box proteins (BBXs) function as central players in these light‐mediated developmental processes. B‐box proteins are a class of zinc‐coordinated transcription factors or regulators that not only directly mediate the transcription of target genes but also interact with various other factors to create a complex regulatory network involved in the precise control of plant growth and development. This review summarizes and highlights the recent findings concerning the critical regulatory functions of BBXs in photoperiodic flowering, light signal transduction and light‐induced pigment accumulation and their molecular modes of action at the transcriptional and post‐translational levels in plants

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    Light signaling and UV-B-mediated plant growth regulation
    Arpita Yadav, Deeksha Singh, Maneesh Lingwan, Premachandran Yadukrishnan, Shyam Kumar Masakapalli and Sourav Datta
    J Integr Plant Biol 2020, 62 (9): 1270-1292.  
    doi: 10.1111/jipb.12932
    Abstract (Browse 373)  |   Save

    Light plays an important role in plants’ growth and development throughout their life cycle. Plants alter their morphological features in response to light cues of varying intensity and quality. Dedicated photoreceptors help plants to perceive light signals of different wavelengths. Activated photoreceptors stimulate the downstream signaling cascades that lead to extensive gene expression changes responsible for physiological and developmental responses. Proteins such as ELONGATED HYPOCOTYL5 (HY5) and CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1) act as important factors which modulate light‐regulated gene expression, especially during seedling development. These factors function as central regulatory intermediates not only in red, far‐red, and blue light pathways but also in the UV‐B signaling pathway. UV‐B radiation makes up only a minor fraction of sunlight, yet it imparts many positive and negative effects on plant growth. Studies on UV‐B perception, signaling, and response in plants has considerably surged in recent times. Plants have developed different strategies to use UV‐B as a developmental cue as well as to withstand high doses of UV‐B radiation. Plants’ responses to UV‐B are an integration of its cross‐talks with both environmental factors and phytohormones. This review outlines the current developments in light signaling with a major focus on UV‐B‐mediated plant growth regulation.

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    Phototropin- and photosynthesis-dependent mitochondrial positioning in Arabidopsis thaliana mesophyll cells
    Md Sayeedul Islam, Toan Van Nguyen, Wataru Sakamoto and Shingo Takagi
    J Integr Plant Biol 2020, 62 (9): 1352-1371.  
    doi: 10.1111/jipb.12910
    Abstract (Browse 298)  |   Save

    Mitochondria are frequently observed in the vicinity of chloroplasts in photosynthesizing cells, and this association is considered necessary for their metabolic interactions. We previously reported that, in leaf palisade cells of Arabidopsis thaliana, mitochondria exhibit blue‐light‐dependent redistribution together with chloroplasts, which conduct accumulation and avoidance responses under the control of blue‐light receptor phototropins. In this study, precise motility analyses by fluorescent microscopy revealed that the individual mitochondria in palisade cells, labeled with green fluorescent protein, exhibit typical stop‐and‐go movement. When exposed to blue light, the velocity of moving mitochondria increased in 30 min, whereas after 4 h, the frequency of stoppage of mitochondrial movement markedly increased. Using different mutant plants, we concluded that the presence of both phototropin1 and phototropin2 is necessary for the early acceleration of mitochondrial movement. On the contrary, the late enhancement of stoppage of mitochondrial movement occurs only in the presence of phototropin2 and only when intact photosynthesis takes place. A plasma‐membrane ghost assay suggested that the stopped mitochondria are firmly adhered to chloroplasts. These results indicate that the physical interaction between mitochondria and chloroplasts is cooperatively mediated by phototropin2‐ and photosynthesis‐dependent signals. The present study might add novel regulatory mechanism for light‐dependent plant organelle interactions.

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    COP9 signalosome: Discovery, conservation, activity, and function
    Nanxun Qin, Dongqing Xu, Jigang Li and Xingwang Deng
    J Integr Plant Biol 2020, 62 (1): 90-103.  
    doi: 10.1111/jipb.12903
    Abstract (Browse 396)  |   Save

    The COP9 signalosome (CSN) is a conserved protein complex, typically composed of eight subunits (designated as CSN1 to CSN8) in higher eukaryotes such as plants and animals, but of fewer subunits in some lower eukaryotes such as yeasts. The CSN complex is originally identified in plants from a genetic screen for mutants that mimic light‐induced photomorphogenic development when grown in the dark. The CSN complex regulates the activity of cullin‐RING ligase (CRL) families of E3 ubiquitin ligase complexes, and play critical roles in regulating gene expression, cell proliferation, and cell cycle. This review aims to summarize the discovery, composition, structure, and function of CSN in the regulation of plant development in response to external (light and temperature) and internal cues (phytohormones).

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    ZEITLUPE is required for shade avoidance in the wild tobacco Nicotiana attenuata
    Yong Zou, Ran Li and Ian T. Baldwin
    J Integr Plant Biol 2020, 62 (9): 1341-1351.  
    doi: 10.1111/jipb.12880
    Abstract (Browse 336)  |   Save

    Being shaded is a common environmental stress for plants, especially for densely planted crops. Shade decreases red: far‐red (R:FR) ratios that inactivate phytochrome B (PHYB) and subsequently release p̱hytochrome i̱nteraction f̱actors (PIFs). Shaded plants display elongated hypocotyls, internodes, and petioles, hyponastic leaves, early flowering and are inhibited in branching: traits collectively called the shade avoidance syndrome (SAS). ZEITLUPE (ZTL) is a circadian clock component and blue light photoreceptor, which is also involved in floral rhythms and plant defense in Nicotiana attenuata. ztl mutants are hypersensitive to red light and ZTL physically interacts with PHYB, suggesting the involvement of ZTL in R:FR light signaling. Here, we show that N. attenuata ZTL‐silenced plants display a phenotype opposite to that of the SAS under normal light. After simulated shade, the normally induced transcript levels of the SAS marker gene, ATHB2 are attenuated in ZTL‐silenced plants. The auxin signaling pathway, known to be involved in SAS, was also significantly attenuated. Furthermore, NaZTL directly interacts with NaPHYBs, and regulates the transcript levels of PHYBs, PIF3a, PIF7 and PIF8 under shade. Our results suggest that ZTL may regulate PHYB‐ and the auxin‐mediated signaling pathway, which functions in the SAS of N. attenuata.

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    A defect in the PINOID serine/threonine kinase affects leaf shape in cucumber
    Jennifer Mach
    J Integr Plant Biol 2019, 61 (9): 966-967.  
    doi: 10.1111/jipb.12860
    Abstract (Browse 268)  |   Save

    Leaf shape has important implications for optimizing plant architecture for grain crops and horticultural crops. Examination of the cucumber (Cucumis sativus L.) round leaf (rl) mutant by Song et al. (2019) revealed that the PINOID protein kinase affects leaf shape by altering auxin biosynthesis, transport, and signaling.

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    Coordination of light, circadian clock with temperature: The potential mechanisms regulating chilling tolerance in rice
    Xuedan Lu, Yan Zhou, Fan Fan, JunHua Peng and Jian Zhang
    J Integr Plant Biol 2020, 62 (6): 737-760.  
    doi: 10.1111/jipb.12852
    Abstract (Browse 437)  |   Save

    Rice (Oryza sativa L.) is a major staple food crop for over half of the world's population. As a crop species originated from the subtropics, rice production is hampered by chilling stress. The genetic mechanisms of rice responses to chilling stress have attracted much attention, focusing on chilling‐related gene mining and functional analyses. Plants have evolved sophisticated regulatory systems to respond to chilling stress in coordination with light signaling pathway and internal circadian clock. However, in rice, information about light‐signaling pathways and circadian clock regulation and their roles in chilling tolerance remains elusive. Further investigation into the regulatory network of chilling tolerance in rice is needed, as knowledge of the interaction between temperature, light, and circadian clock dynamics is limited. Here, based on phenotypic analysis of transgenic and mutant rice lines, we delineate the relevant genes with important regulatory roles in chilling tolerance. In addition, we discuss the potential coordination mechanism among temperature, light, and circadian clock in regulating chilling response and tolerance of rice, and provide perspectives for the ongoing chilling signaling network research in rice.

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    Photoexcited phytochrome B interacts with brassinazole resistant 1 to repress brassinosteroid signaling in Arabidopsis
    Huixue Dong, Jie Liu, Guanhua He, Pan Liu, Jiaqiang Sun
    J Integr Plant Biol 2020, 62 (5): 652-667.  
    DOI: 10.1111/jipb.12822
    Abstract (Browse 385)  |   Save

    Photoreceptor phytochrome B (phyB) mediates a variety of light responses in plants. To further elucidate the molecular mechanisms of phyB‐regulated hypocotyl elongation, we performed firefly luciferase complementation imaging (LCI) screening for phyB‐interacting transcription factors (TFs). LCI assays showed that phyB possibly interacts with brassinazoleresistant 1 (BZR1), BZR2, AUXIN RESPONSE FACTOR 6 (ARF6), and several WRKY DNA‐binding TFs in a red light‐dependent manner. Furthermore, biochemical assays demonstrated that photoexcited phyB specifically interacts with non‐phosphorylated BZR1, the physiologically active form of a master TF in brassinosteroid (BR) signaling, and this interaction can be competitively interfered by phytochrome‐interacting factor 4. Furthermore, we showed that phyB can directly interact with the DNA‐binding domain of BZR1 and affect the enrichment of BZR1 on the chromatin of target genes. Moreover, our genetic evidence and RNA‐seq analysis demonstrated that phyB negatively regulates BR signaling. Together, we revealed that photoexcited phyB directly interacts with the TF BZR1 to repress BR signaling in Arabidopsis.

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    Cryptochrome‐mediated hypocotyl phototropism was regulated antagonistically by gibberellic acid and sucrose in Arabidopsis
    Qing-Ping Zhao, Jin-Dong Zhu, Nan-Nan Li, Xiao-Nan Wang, Xiang Zhao and Xiao Zhang
    J Integr Plant Biol 2020, 62 (5): 614-630.  
    doi: 10.1111/jipb.12813
    Abstract (Browse 346)  |   Save

    Both phototropins (phot1 and phot2) and cryptochromes (cry1 and cry2) were proven as the Arabidopsis thaliana blue light receptors. Phototropins predominately function in photomovement, and cryptochromes play a role in photomorphogenesis. Although cryptochromes have been proposed to serve as positive modulators of phototropic responses, the underlying mechanism remains unknown. Here, we report that depleting sucrose from the medium or adding gibberellic acids (GAs) can partially restore the defects in phototropic curvature of the phot1 phot2 double mutants under high‐intensity blue light; this restoration does not occur in phot1 phot2 cry1 cry2 quadruple mutants and nph3 (nonphototropic hypocotyl 3) mutants which were impaired phototropic response in sucrose‐containing medium. These results indicate that GAs and sucrose antagonistically regulate hypocotyl phototropism in a cryptochromes dependent manner, but it showed a crosstalk with phototropin signaling on NPH3. Furthermore, cryptochromes activation by blue light inhibit GAs synthesis, thus stabilizing DELLAs to block hypocotyl growth, which result in the higher GAs content in the shade side than the lit side of hypocotyl to support the asymmetric growth of hypocotyl. Through modulation of the abundance of DELLAs by sucrose depletion or added GAs, it revealed that cryptochromes have a function in mediating phototropic curvature.

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