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Authors: Arnau Rovira, Nil Veciana, Aina Basté-Miquel, Martí Quevedo, Antonella Locascio, Lynne Yenush, Gabriela Toledo-Ortiz, Pablo Leivar and Elena Monte.
Nature Communications (2024)
Editor's view: Stomata function is essential for photosynthesis and the global carbon and oxygen cycles. Here, the authors report the regulatory framework that establishes rhythmic pore movements to prevent water loss at night and allow CO2 uptake during the day.
Abstract: "Stomata govern the gaseous exchange between the leaf and the external atmosphere, and their function is essential for photosynthesis and the global carbon and oxygen cycles. Rhythmic stomata movements in daily dark/light cycles prevent water loss at night and allow CO2 uptake during the day. How the actors involved are transcriptionally regulated and how this might contribute to rhythmicity is largely unknown. Here, we show that morning stomata opening depends on the previous night period. The transcription factors PHYTOCHROME-INTERACTING FACTORS (PIFs) accumulate at the end of the night and directly induce the guard cell-specific K+ channel KAT1. Remarkably, PIFs and KAT1 are required for blue light-induced stomata opening. Together, our data establish a molecular framework for daily rhythmic stomatal movements under well-watered conditions, whereby PIFs are required for accumulation of KAT1 at night, which upon activation by blue light in the morning leads to the K+ intake driving stomata opening."
Authors: Kalyan Mahapatra, Shubhi Dwivedi, Arpan Mukherjee, Ajar Anupam Pradhan, Kavuri Venkateswara Rao, Deeksha Singh, Lavanya Bhagavatula and Sourav Datta.
Journal of Experimental Botany (2024)
Abstract: "The exogenous light cues and the phytohormone Abscisic acid (ABA) regulate several aspects of plant growth and development. In recent years, the role of the crosstalk between the light and ABA signaling pathways in regulating different physiological processes has become increasingly evident. This includes the regulation of germination and early seedling development, control of stomatal development and conductance, growth and development of roots, buds, branches, and regulation of flowering. Light and ABA signaling cascades have various convergence points at both DNA and protein levels. The molecular crosstalk involves several light signaling factors like HY5, COP1, PIFs and BBXs that integrate with ABA signaling components like the PYL receptors and ABI5. Especially, ABI5 and PIF4 promoters serve as key “hotspots” for the integration of these two pathways. Plants acquired both light and ABA signaling pathways before they colonized land almost 500 million years ago. In this review, we discuss the recent advances in the interplay of light and ABA signaling regulating plant development and provide an overview of the evolution of these two pathways."
Authors: Jingbo Zhang, Xuexue Chen, Yajing Song and Zhizhong Gong.
Journal of Integrative Plant Biology (2024)
One-sentence summary: This review summarizes current knowledge on the molecular mechanisms of stomatal movements mediated by abscisic acid, light, CO2, reactive oxygen species, pathogens, temperature, and other phytohormones, which helps in designing smart crops with higher resilience.
Abstract: "Global climate change-caused drought stress, high temperatures and other extreme weather profoundly impact plant growth and development, restricting sustainable crop production. To cope with various environmental stimuli, plants can optimize the opening and closing of stomata to balance CO2 uptake for photosynthesis and water loss from leaves. Guard cells perceive and integrate various signals to adjust stomatal pores through turgor pressure regulation. Molecular mechanisms and signaling networks underlying the stomatal movements in response to environmental stresses have been extensively studied and elucidated. This review focuses on the molecular mechanisms of stomatal movements mediated by abscisic acid, light, CO2, reactive oxygen species, pathogens, temperature, and other phytohormones. We discussed the significance of elucidating the integrative mechanisms that regulate stomatal movements in helping design smart crops with enhanced water use efficiency and resilience in a climate-changing world."
Authors: Esther Cañibano, Daniela Soto-Gomez, Juan Carlos Oliveros, Clara Bourbousse and Sandra Fonseca.
bioRxiv (2024)
Abstract: "Driven by cell elongation, hypocotyl growth is tightly controlled by light and responds to external stimuli and endogenous hormonal pathways. Hypocotyls are known to be responsive to the stress signalling hormone abscisic acid (ABA) which effectively inhibits cell elongation, but how this regulation is connected to light responses and other endogenous hormonal pathways has been a subject of limited studies. Here, we show that whereas hypocotyl elongation is sensitive to ABA in light-grown seedlings, the hypocotyl of dark-grown etiolated seedlings is ABA-insensitive. In the dark, hypocotyl sensitivity to ABA is restored in the constitutive photomorphogenic pifq and cop1-4 mutants, suggesting that an active light signalling pathway is necessary for hypocotyl responsiveness to ABA. However, etiolated hypocotyls retain ABA responsiveness, as could be detected by the induction of ABI1 and RD29B transcripts in response to exogenous ABA, suggesting that inhibition of hypocotyl elongation mediated by ABA does not follows the canonical ABA signalling dependent on transcription. Here, using RNA-seq analysis we identified a number of ABA differentially expressed genes (DEGs) that correlate with ABA inhibition of hypocotyl elongation, specifically in dark-grown pifq or light-grown WT plants, and whose expression remains unchanged by ABA treatment in dark-grown WT plants. Among these DEGs we identified a number of genes playing a role in cell elongation directly at the level of the plasma membrane, as SAURs, ion transporters, auxin flux regulators, channels, and cell wall modification enzymes. The use of the auxin transport inhibitor, NPA, revealed that in the light auxin transport impairment renders hypocotyls insensitive to ABA in WT and pifq plants. Thus, in the light, hypocotyl responsiveness to ABA is dependent on auxin transport and independent of PIFs. In the dark, PIFs render hypocotyls insensitive to ABA, perhaps by regulating the expression of a number of ABA DEGs, a mechanism that could allow plants to prioritize the elongation towards light, avoiding to slow-down soil emergence that could be induced by ABA signalling in case of sudden reduction of soil moisture."
Authors: Hong Li, Yangyang Zhou, Xinyan Qin, Jing Peng, Run Han, Yang Lv, Cong Li, Lijuan Qi, Gao-Ping Qu, Li Yang, Yanjie Li, William Terzaghi, Zhen Li, Feng Qin, Zhizhong Gong, Xing Wang Deng and Jigang Li.
PNAS (2023)
Significance: ABA (Abscisic acid) plays a crucial role in modulating plant responses to abiotic stress, and the ABA signaling mechanisms have been extensively investigated. Here, we reconstituted a complete ABA signaling pathway, from hormone perception to ABA-responsive gene expression, in yeast. Employing this system, we evaluated roles of additional components, including phytochromes and RAFs, in regulating ABA signaling. We showed that phyA (phytochrome A) attenuated ABA signaling by directly interacting with key components of the core ABA signaling module. In addition, we revealed that a conserved threonine in the activation loop of RAFs is critical for RAF activation of SnRK2s (sucrose nonfermenting1-related protein kinase 2s). Together, our system may help expedite ABA research by simplifying the complicated ABA signaling pathways in yeast.
Abstract: "Abscisic acid (ABA), a classical plant hormone, plays an essential role in plant adaptation to environmental stresses. The ABA signaling mechanisms have been extensively investigated, and it was shown that the PYR1 (PYRABACTIN RESISTANCE1)/PYL (PYR1-LIKE)/RCAR (REGULATORY COMPONENT OF ABA RECEPTOR) ABA receptors, the PP2C coreceptors, and the SnRK2 protein kinases constitute the core ABA signaling module responsible for ABA perception and initiation of downstream responses. We recently showed that ABA signaling is modulated by light signals, but the underlying molecular mechanisms remain largely obscure. In this study, we established a system in yeast cells that was not only successful in reconstituting a complete ABA signaling pathway, from hormone perception to ABA-responsive gene expression, but also suitable for functionally characterizing the regulatory roles of additional factors of ABA signaling. Using this system, we analyzed the roles of several light signaling components, including the red and far-red light photoreceptors phytochrome A (phyA) and phyB, and the photomorphogenic central repressor COP1, in the regulation of ABA signaling. Our results showed that both phyA and phyB negatively regulated ABA signaling, whereas COP1 positively regulated ABA signaling in yeast cells. Further analyses showed that photoactivated phyA interacted with the ABA coreceptors ABI1 and ABI2 to decrease their interactions with the ABA receptor PYR1. Together, data from our reconstituted yeast ABA signaling system provide evidence that photoactivated photoreceptors attenuate ABA signaling by directly interacting with the key components of the core ABA signaling module, thus conferring enhanced ABA tolerance to light-grown plants."
Authors: Rahul Michael, Shagun Bali, Ritu Godara and Vivek Dogra.
Trends in Plant Science (2023)
Abstract: "Seed thermoinhibition protects emerging seedlings from thermodamage by preventing seed germination at elevated temperatures. It had remained unknown how a seed fine-tunes its germination in response to temperature. Recently, Piskurewicz et al. demonstrated that endosperm phyB senses increased temperature, thereby facilitating PIF3-mediated abscisic acid (ABA) accumulation to inhibit germination and embryo elongation."
Excerpts: "A Swiss team, led by scientists from the University of Geneva (UNIGE), has discovered an internal thermometer of seeds that can delay or even block germination if temperatures are too high for the future seedling. This work could help optimize plant growth in the context of global warming. These results can be read in the journal Nature Communications."
"However, non-dormant seeds can still decide their fate. For example, a non-dormant seed that is suddenly subjected to excessively high temperatures (greater than 28°C) can block germination. This mechanism of repression by temperature (thermo-inhibition) allows a very fine regulation. A variation of only 1 to 2°C can indeed delay the germination of a seed population and thus increase the chances of survival of future seedlings."
""We found that thermo-inhibition in Arabidopsis is not autonomously controlled by the embryo but implemented by the endosperm, revealing a new essential function for this tissue," explains Urszula Piskurewicz, researcher at the Department of Plant Sciences of the UNIGE Faculty of Science and first author of the study. "In other words, in the absence of endosperm, the embryo within the seed would not perceive that the temperatures are too high and would begin its germination, which would be fatal."
Authors: Zsuzsanna Mérai, Fei Xu, Andreas Musilek, Florian Ackerl, Sarhan Khalil, Luz Mayela Soto-Jiménez, Katarina Lalatović, Cornelia Klose, Danuše Tarkowská, Veronika Turečková, Miroslav Strnad and Ortrun Mittelsten Scheid.
Plant Physiology (2023)
Abstract: "The view on the role of light during seed germination stems mainly from studies with Arabidopsis (Arabidopsis thaliana), where light is required to initiate this process. In contrast, white light is a strong inhibitor of germination in other plants, exemplified by accessions of Aethionema arabicum, another member of Brassicaceae. Their seeds respond to light with gene expression changes of key regulators converse to that of Arabidopsis, resulting in opposite hormone regulation and prevention of germination. However, the photoreceptors involved in this process in A. arabicum remain unknown. Here, we screened a mutant collection of A. arabicum and identified koy-1, a mutant that lost light inhibition of germination due to a deletion in the promoter of HEME OXYGENASE 1, the gene for a key enzyme in the biosynthesis of the phytochrome chromophore. koy-1 seeds were unresponsive to red- and far-red light and hyposensitive under white light. Comparison of hormone and gene expression between wild type and koy-1 revealed that very low light fluence stimulates germination, while high irradiance of red and far-red light is inhibitory, indicating a dual role of phytochromes in light-regulated seed germination. The mutation also affects the ratio between the two fruit morphs of A. arabicum, suggesting that light reception via phytochromes can fine-tune several parameters of propagation in adaptation to conditions in the habitat."
Authors: Gaële Lajeunesse, Charles Roussin-Léveillée, Sophie Boutin, Élodie Fortin, Isabelle Laforest-Lapointe and Peter Moffett.
Nature Communications (2023)
Editor's view: Pseudomonas syringae alters plant abscisic acid signaling to close stomata and induce water accumulation in infected tissues. Light and salicylic acid counteract infection by promoting stomatal opening, depriving bacteria of an aqueous environment.
Abstract: "Many plant pathogens induce water-soaked lesions in infected tissues. In the case of Pseudomonas syringae (Pst), water-soaking effectors stimulate abscisic acid (ABA) production and signaling, resulting in stomatal closure. This reduces transpiration, increases water accumulation, and induces an apoplastic microenvironment favorable for bacterial growth. Stomata are sensitive to environmental conditions, including light. Here, we show that a period of darkness is required for water-soaking, and that a constant light regime abrogates stomatal closure by Pst. We find that constant light induces resistance to Pst, and that this effect requires salicylic acid (SA). Constant light did not alter effector-induced accumulation of ABA, but induced greater SA production, promoting stomatal opening despite the presence of ABA. Furthermore, application of a SA analog was sufficient to prevent pathogen-induced stomatal closure and water-soaking. Our results suggest potential approaches for interfering with a common virulence strategy, as well as providing a physiological mechanism by which SA functions in defense against pathogens."
Authors: Vishal Varshney, Abhijit Hazra and Manoj Majee.
Trends in Plant Science (2023)
Abstract: "The complex process of seed germination is impacted heavily by environmental cues, such as light, mediated via photosensory systems and phytochromes. This pathway was discovered a long time ago, but the underlying molecular mechanisms are not fully understood. Li et al. recently showed how ETHYLENE RESPONSE FACTORs (ERFs) modulate phytochrome-mediated regulation of germination."
Authors: Olivier Michaud, Johanna Krahmer, Florian Galbier, Maud Lagier, Vinicius Costa Galvão, Yetkin Çaka Ince, Martine Trevisan, Jana Knerova, Patrick Dickinson, Julian M. Hibberd, Samuel C. Zeeman and Christian Fankhauser.
Plant Physiology (2023)
Abstract: "Leaves of shade-avoiding plants such as Arabidopsis (Arabidopsis thaliana) change their growth pattern and position in response to low red to far-red ratios (LRFRs) encountered in dense plant communities. Under LRFR, transcription factors of the phytochrome interacting factor (PIF) family are de-repressed. PIFs induce auxin production, which is required for promoting leaf hyponasty, thereby favoring access to unfiltered sunlight. Abscisic acid (ABA) has also been implicated in the control of leaf hyponasty, with gene expression patterns suggesting that LRFR regulates the ABA response. Here, we show that LRFR leads to a rapid increase in ABA levels in leaves. Changes in ABA levels depend on PIFs, which regulate the expression of genes encoding isoforms of the enzyme catalyzing a rate-limiting step in ABA biosynthesis. Interestingly, ABA biosynthesis and signaling mutants have more erect leaves than wild-type Arabidopsis under white light but respond less to LRFR. Consistent with this, ABA application decreases leaf angle under white light; however, this response is inhibited under LRFR. Tissue-specific interference with ABA signaling indicates that an ABA response is required in different cell types for LRFR-induced hyponasty. Collectively, our data indicate that LRFR triggers rapid PIF-mediated ABA production. ABA plays a different role in controlling hyponasty under white light than under LRFR. Moreover, ABA exerts its activity in multiple cell types to control leaf position."
Authors: Hongyun Zhao, Yamei Zhang and Yuan Zheng.
Frontiers in Plant Science (2022)
Abstract: "Seed germination is precisely controlled by a variety of signals, among which light signals and the phytohormones abscisic acid (ABA) and gibberellin (GA) play crucial roles. New findings have greatly increased our understanding of the mechanisms by which these three signals regulate seed germination and the close connections between them. Although much work has been devoted to ABA, GA, and light signal interactions, there is still no systematic description of their combination, especially in seed germination. In this review, we integrate ABA, GA, and light signaling in seed germination through the direct and indirect regulation of ABSCISIC ACID INSENSITIVE5 (ABI5), the core transcription factor that represses seed germination in ABA signaling, into our current understanding of the regulatory mechanism of seed germination.
Authors: Muhammad Awais Farooq,Wei Ma, Shuxing Shen and Aixia Gu.
International Journal of Molecular Sciences (2022)
Abstract: "With the burgeoning population of the world, the successful germination of seeds to achieve maximum crop production is very important. Seed germination is a precise balance of phytohormones, light, and temperature that induces endosperm decay. Abscisic acid and gibberellins—mainly with auxins, ethylene, and jasmonic and salicylic acid through interdependent molecular pathways—lead to the rupture of the seed testa, after which the radicle protrudes out and the endosperm provides nutrients according to its growing energy demand. The incident light wavelength and low and supra-optimal temperature modulates phytohormone signaling pathways that induce the synthesis of ROS, which results in the maintenance of seed dormancy and germination. In this review, we have summarized in detail the biochemical and molecular processes occurring in the seed that lead to the germination of the seed. Moreover, an accurate explanation in chronological order of how phytohormones inside the seed act in accordance with the temperature and light signals from outside to degenerate the seed testa for the thriving seed’s germination has also been discussed."
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Authors: Pierre Gautrat, Sanne E. A. Matton, Lisa Oskam, Siddhant S. Shetty, Kyra J. van der Velde and Ronald Pierik.
Journal of Experimental Botany (2024)
Abstract: "Plants growing in dense vegetation stands need to flexibly position their photosynthetic organs to ensure optimal light capture in a competitive environment. They do so through a suite of developmental responses referred to as the shade avoidance syndrome. Belowground, root development is also adjusted in response to aboveground neighbour proximity. Canopies are dynamic and complex environments with heterogeneous light cues in the far-red, red, blue and UV spectrum, which can be perceived with photoreceptors by spatially separated plant tissues. Molecular regulation of plant architecture adjustment via PHYTOCHROME-INTERACTING FACTOR (PIF) transcription factors and growth-related hormones such as auxin, gibberellic acid, brassinosteroids and abscisic acid were historically studied without much attention to spatial or tissue-specific context. Recent developments and technologies have, however, sparked strong interest in spatially explicit understanding of shade avoidance regulation. Other environmental factors such as temperature and nutrient availability interact with the molecular shade avoidance regulation network, often depending on the spatial location of the signals, and the responding organs. Here, we aim to review recent advances in how plants respond to heterogenous light cues and integrate these with other environmental signals."
Authors: Xiaofeng Luo, Yujia Dai, Baoshan Xian, Jiahui Xu, Ranran Zhang, Muhammad Saad Rehmani, Chuan Zheng, Xiaoting Zhao, Kaitao Mao, Xiaotong Ren, Shaowei Wei, Lei Wang, Juan He, Weiming Tan, Junbo Du, Weiguo Liu, Shu Yuan and Kai Shu.
Journal of Integrative Plant Biology (2024)
Abstract: "Transcriptional regulation plays a key role in the control of seed dormancy, and many transcription factors (TFs) have been documented. However, the mechanisms underlying the interactions between different TFs within a transcriptional complex regulating seed dormancy remain largely unknown. Here, we showed that TF PHYTOCHROME-INTERACTING FACTOR4 (PIF4) physically interacted with the abscisic acid (ABA) signaling responsive TF ABSCISIC ACID INSENSITIVE4 (ABI4) to act as a transcriptional complex to promote ABA biosynthesis and signaling, finally deepening primary seed dormancy. Both pif4 and abi4 single mutants exhibited a decreased primary seed dormancy phenotype, with a synergistic effect in the pif4/abi4 double mutant. PIF4 binds to ABI4 to form a heterodimer, and ABI4 stabilizes PIF4 at the protein level, whereas PIF4 does not affect the protein stabilization of ABI4. Subsequently, both TFs independently and synergistically promoted the expression of ABI4 and NCED6, a key gene for ABA anabolism. The genetic evidence is also consistent with the phenotypic, physiological and biochemical analysis results. Altogether, this study revealed a transcriptional regulatory cascade in which the PIF4–ABI4 transcriptional activator complex synergistically enhanced seed dormancy by facilitating ABA biosynthesis and signaling."
Authors: Seoyeon Cha, Wang Ki Min and Hak Soo Seo
Communications Biology (2024)
One-sentence summary: Arabidopsis E3 ubiquitin ligase CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) suppresses the activity of plasma membrane H+-ATPase, thereby maintaining proper pH profiles of the guard cells and subsequent stomatal responses.
Abstract: "Plants rely on precise regulation of their stomatal pores to effectively carry out photosynthesis while managing water status. The Arabidopsis CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1), a critical light signaling repressor, is known to repress stomatal opening, but the exact cellular mechanisms remain unknown. Here, we show that COP1 regulates stomatal movement by controlling the pH levels in guard cells. cop1-4 mutants have larger stomatal apertures and disrupted pH dynamics within guard cells, characterized by increased vacuolar and cytosolic pH and reduced apoplastic pH, leading to abnormal stomatal responses. The altered pH profiles are attributed to the increased plasma membrane (PM) H+-ATPase activity of cop1-4 mutants. Moreover, cop1-4 mutants resist to growth defect caused by alkali stress posed on roots. Overall, our study highlights the crucial role of COP1 in maintaining pH homeostasis of guard cells by regulating PM H+-ATPase activity, and demonstrates how proton movement affects stomatal movement and plant growth."
Authors: Yanna Xu, Congjun You, Changbin Xu, Chaofan Zhang, Xiaoli Hu, Xiaolong Li, Haijie Ma, Jinli Gong and Xuepeng Sun.
Postharvest Biology and Technology (2024)
Highlights: • Skin coloration of tomato fruit responds differentially to red and blue light. • Both lights promote biosynthesis of carotenoids and phytohormones. • Gene modules associated with carotenoid and hormone metabolism were identified. • Transcription factors as key regulators of the modules were uncovered. • A working model was proposed to depict the light regulation of fruit coloration.
Abstract: "Understanding how light regulates pigment composition and accumulation is crucial for postharvest management of fruit quality and nutritional value. In this study, we investigated the influence of light quality, specifically the blue and red lights, on coloration of tomato fruit. We show that both lights expedite the progress of skin coloration in tomato fruit by promoting chlorophyll degradation, stimulating carotenoid biosynthesis, accelerating plastid conversion, and enhancing plant hormone (i.e., abscisic acid and ethylene) biosynthesis. However, red light shows higher efficiency in inducing color transition compared with blue light. Gene expression network analysis unraveled several modules that are associated with carotenoid metabolism and hormone biosynthesis in response to light treatments, among which the transcription factors including WRKY20, MYB12, ARR11, NAC16, bHLH46, ZNF69, and MYB58 were identified as potential key regulators. Collectively, our data provide new threads on the regulation of fruit coloration by light quality and highlight the potential utility of red LED treatment to improve the color and quality of tomato fruit."
Authors: Miguel Ezquerro, Esteban Burbano-Erazo and Manuel Rodriguez-Concepcion.
Plant Physiology (2023)
One-sentence summary: The main flux-controlling step of the carotenoid pathway in tomato is catalyzed by a small family of enzymes that differentially contribute to the biosynthesis of carotenoids and derived hormones.
Abstract: "Carotenoids are plastidial isoprenoids required for photosynthesis and phytohormone production in all plants. In tomato (Solanum lycopersicum), carotenoids also provide color to flowers and ripe fruit. Phytoene synthase (PSY) catalyzes the first and main flux-controlling step of the carotenoid pathway. Three genes encoding PSY isoforms are present in tomato, PSY1 to PSY3. Mutants have shown that PSY1 is the isoform providing carotenoids for fruit pigmentation, but it is dispensable in photosynthetic tissues. No mutants are available for PSY2 or PSY3, but their expression profiles suggest a main role for PSY2 in leaves and PSY3 in roots. To further investigate isoform specialization with genetic tools, we created gene-edited lines defective in PSY1 and PSY2 in the MicroTom background. The albino phenotype of lines lacking both PSY1 and PSY2 confirmed that PSY3 does not contribute to carotenoid biosynthesis in shoot tissues. Our work further showed that carotenoid production in tomato shoots relies on both PSY1 and PSY2 but with different contributions in different tissues. PSY2 is the main isoform for carotenoid biosynthesis in leaf chloroplasts, but PSY1 is also important in response to high light. PSY2 also contributes to carotenoid production in flower petals and, to a lesser extent, fruit chromoplasts. Most interestingly, our results demonstrate that fruit growth is controlled by abscisic acid (ABA) specifically produced in the pericarp from PSY1-derived carotenoid precursors, whereas PSY2 is the main isoform associated with ABA synthesis in seeds and salt-stressed roots."
Authors: Yanyan Wang, Yuqin Xiao, Yueting Sun, Xiang Zhang, Bingyang Du, Maihemuti Turupu, Qisheng Yao, Shilin Gai, Shi Tong, Jing Huang and Tianhong Li.
Plant Physiology (2023)
Abstract: "Anthocyanin production in bicolored sweet cherry (Prunus avium cv. Rainier) fruit is induced by light exposure, leading to red coloration. The phytohormone abscisic acid (ABA) is essential for this process, but the regulatory relationships that link light and ABA with anthocyanin-associated coloration are currently unclear. In this study, we determined that light treatment of bicolored sweet cherry fruit increased anthocyanin accumulation and induced ABA production and that ABA participates in light-modulated anthocyanin accumulation in bicolored sweet cherry. Two B-box (BBX) genes, PavBBX6/9, were highly induced by light and ABA treatments, as was anthocyanin accumulation. The ectopic expression of PavBBX6 or PavBBX9 in Arabidopsis (Arabidopsis thaliana) increased anthocyanin biosynthesis and ABA accumulation. Overexpressing PavBBX6 or PavBBX9 in sweet cherry calli also enhanced light-induced anthocyanin biosynthesis and ABA accumulation. Additionally, transient overexpression of PavBBX6 or PavBBX9 in sweet cherry peel increased anthocyanin and ABA contents, whereas silencing either gene had the opposite effects. PavBBX6 and PavBBX9 directly bound to the G-box elements in the promoter of UDP glucose-flavonoid-3-O-glycosyltransferase (PavUFGT), a key gene for anthocyanin biosynthesis, and 9-cis-epoxycarotenoid dioxygenase 1 (PavNCED1), a key gene for ABA biosynthesis, and enhanced their activities. These results suggest that PavBBX6 and PavBBX9 positively regulate light-induced anthocyanin and ABA biosynthesis by promoting PavUFGT and PavNCED1 expression, respectively. Our study provides insights into the relationship between the light-induced ABA biosynthetic pathway and anthocyanin accumulation in bicolored sweet cherry fruit."
Authors: Urszula Piskurewicz, Maria Sentandreu, Mayumi Iwasaki, Gaëtan Glauser and Luis Lopez-Molina.
Nature Communications (2023)
Editor's view: Piskurewicz et al. show that seed thermoinhibition is controlled by endospermic phytochrome B (phyB). High temperature decreases endospermic phyB signaling, which promotes DELLA- and PIF-mediated endospermic ABA release that blocks germination.
Abstract: "Seed thermoinhibition, the repression of germination under high temperatures, prevents seedling establishment under potentially fatal conditions. Thermoinhibition is relevant for phenology and agriculture, particularly in a warming globe. The temperature sensing mechanisms and signaling pathways sustaining thermoinhibition are unknown. Here we show that thermoinhibition in Arabidopsis thaliana is not autonomously controlled by the embryo but is rather implemented by the endosperm. High temperature is sensed through endospermic phyB by accelerating its reversion from the active signaling Pfr form into the inactive Pr form, as previously described in seedlings. This leads to thermoinhibition mediated by PIFs, mainly PIF1, PIF3 and PIF5. Endospermic PIF3 represses the expression of the endospermic ABA catabolic gene CYP707A1 and promotes endospermic ABA accumulation and release towards the embryo to block its growth. Furthermore, endospermic ABA represses embryonic PIF3 accumulation that would otherwise promote embryonic growth. Hence, under high temperatures PIF3 exerts opposite growth responses in the endosperm and embryo."
Authors: Jiakai Liao, Ban Deng, Qixin Yang, Yu Li, Yuxiang Zhang, Jiajing Cong, Xiaqin Wang, Markus V. Kohnen, Zhong-Jian Liu, Meng-Zhu Lu, Deshu Lin, Lianfeng Gu and Bobin Liu.
New Phytologist (2023)
Abstract: "The acquisition of dormancy capabilities has enabled plants to survive in adverse terrestrial environmental conditions. Dormancy accumulation and release is coupled with light signaling, which is well studied in Arabidopsis, but it is unclear in the distant nonvascular relative. We study the characteristics and function on dormancy regulation of a blue light receptor cryptochrome in Marchantia polymorpha (MpCRY). Here, we identified MpCRY via bioinformatics and mutant complement analysis. The biochemical characteristics were assessed by multiple protein-binding assays. The function of MpCRY in gemma dormancy was clarified by overexpression and mutation of MpCRY, and its mechanism was analyzed via RNA sequencing and quantitative PCR analyses coupled with hormone treatment. We found that the unique MpCRY protein in M. polymorpha undergoes both blue light-promoted interaction with itself (self-interaction) and blue light-dependent phosphorylation. MpCRY has the specific characteristics of blue light-induced nuclear localization and degradation. We further demonstrated that MpCRY transcriptionally represses abscisic acid (ABA) signaling-related gene expression to suppress gemma dormancy, which is dependent on blue light signaling. Our findings indicate that MpCRY possesses specific biochemical and molecular characteristics, and modulates ABA signaling under blue light conditions to regulate gemma dormancy in M. polymorpha.
Authors: Yuqiu Wang, Yangyang Fan, De Fan, Xiaoli Zhou, Yuntong Jiao, Xing Wang Deng and Danmeng Zhu.
The Plant Cell (2023)
Abstract: "Light is a major environmental factor for seed germination. Red-light-activated phytochrome B (phyB) promotes seed germination by modulating the dynamic balance of two phytohormones, gibberellic acid (GA) and abscisic acid (ABA). How phyB modulates ABA biosynthesis after perceiving a light signal is not yet well understood. Here, we identified the noncoding RNA HIDDEN TREASURE 1 (HID1) as a repressor of ABA biosynthesis acting downstream of phyB during Arabidopsis thaliana seed germination. Loss of HID1 function led to delayed phyB-dependent seed germination. Photo-activated phyB promoted the accumulation of HID1 in the radicle within 48 hours of imbibition. Our transcriptomics analysis showed that HID1 and phyB co-regulate the transcription of a common set of genes involved in ABA and GA metabolism. Through a forward genetic screen, we identified three ABA biosynthesis genes, ABA DEFICIENT 1 (ABA1), ABA2, and ABA3, as suppressors of HID1. We further demonstrated that HID1 directly inhibits the transcription of 9-CIS-EPOXYCAROTENOID DIOXYGENASE (NCED9), a gene encoding a key rate-limiting enzyme of ABA biosynthesis. HID1 interacts with ARABIDOPSIS TRITHORAX-RELATED7 (ATXR7), an H3K4me3 methyltransferase, inhibiting its occupancy and H3K4me3 modification at the NCED9 locus. Our study reveals a nuclear mechanism of phyB signaling transmitted through HID1 to control the internal homeostasis of ABA and GA, which gradually optimizes the transcriptional network during seed germination."
Authors: Yadukrishnan Premachandran and José Manuel Ugalde.
Plant Physiology (2023)
Excerpt: "Shade avoidance is a remarkable example of the plasticity exhibited by plants in response to environmental signals. Shade avoiding plants need to perform an array of morphogenic adjustments upon the sensing of changes in light quality. Such changes in light are perceived as a decrease in the ratio of red to far-red (R/FR) wavelengths caused, for example, by neighboring plants competing for light (Ballaré and Pierik, 2017). One of the signature responses to low R/FR (LRFR) involves upward repositioning of leaves to maximize light capture, known as hyponasty. Although the pivotal function of auxin in regulating LRFR-induced hyponasty has been well studied (Michaud et al., 2017; Pantazopoulou et al., 2017), knowledge on the role of other phytohormones in this phenomenon is scarce. In this issue of Plant Physiology, Michaud et al. (2022) report that abscisic acid (ABA) plays a crucial role in mediating LRFR-induced hyponasty. They demonstrate that exposure to LRFR rapidly increases the biosynthesis of ABA, which is necessary for the upward movement of leaves in the proximity of competing neighbors."
Authors: Songbei Ying, Wenjun Yang, Ping Li, Yulan Hu, Shiyan Lu, Yun Zhou, Jinling Huang, John T. Hancock and Xiangyang Hu.
EMBO reports (2022)
Synopsis: High temperature and photoreceptor phytochrome B antagonistically modulate the S-nitrosylation level of HFR1 to coordinate seed germination. High temperature (HT) stimulates the S-nitrosylation of HFR1 at C164 and its degradation, thereby releasing PIF1 to induce SOMNUS (SOM) expression and seed dormancy. Active phyB antagonizes HT-induced S-nitrosylation and degradation of HFR1 by increasing S-nitrosoglutathione reductase (GSNOR) activity. Substituting cysteine-164 of HFR1 with serine (HFR1C164S) abolishes the HT-induced S-nitrosylation of HFR1 and decreases its degradation, ultimately suppressing SOM expression to enhance seed thermotolerance.
Abstract: "Light and ambient high temperature (HT) have opposite effects on seed germination. Light induces seed germination through activating the photoreceptor phytochrome B (phyB), resulting in the stabilization of the transcription factor HFR1, which in turn sequesters the suppressor PIF1. HT suppresses seed germination and triggers protein S-nitrosylation. Here, we find that HT suppresses seed germination by inducing the S-nitrosylation of HFR1 at C164, resulting in its degradation, the release of PIF1, and the activation of PIF1-targeted SOMNUS (SOM) expression to alter gibberellin (GA) and abscisic acid (ABA) metabolism. Active phyB (phyBY276H) antagonizes HFR1 S-nitrosylation and degradation by increasing S-nitrosoglutathione reductase (GSNOR) activity. In line with this, substituting cysteine-164 of HFR1 with serine (HFR1C164S) abolishes the S-nitrosylation of HFR1 and decreases the HT-induced degradation of HFR1. Taken together, our study suggests that HT and phyB antagonistically modulate the S-nitrosylation level of HFR1 to coordinate seed germination, and provides the possibility to enhance seed thermotolerance through gene-editing of HFR1."
Authors: Qian Li, Luyan Zhou, Yanan Chen, Ning Xiao, Dongping Zhang, Mengjiao Zhang, Wenguo Wang, Changquan Zhang, Anning Zhang, Hua Li, Jianmin Chen and Yong Gao.
The Plant Cell (2022)
Abstract: "Stomata are crucial valves coordinating the fixation of carbon dioxide by photosynthesis and water loss through leaf transpiration. Phytochrome interacting factors (PIFs) are negative regulators of red light responses that belong to the basic helix-loop-helix (bHLH) family of transcription factors. Here, we show that the rice (Oryza sativa) PIF family gene OsPIL15 acts as a negative regulator of stomatal aperture to control transpiration in rice. OsPIL15 reduces stomatal aperture by activating rice ABSCISIC ACID INSENSITIVE 5 (OsABI5), which encodes a critical positive regulator of abscisic acid (ABA) signaling in rice. Moreover, OsPIL15 interacts with the NIGT1/HRS1/HHO family transcription factor rice HRS1 HOMOLOG 3 (OsHHO3) to possibly enhance the regulation of stomatal aperture. Notably, we discovered that the maize (Zea mays) PIF family genes ZmPIF1 and ZmPIF3, which are homologous to OsPIL15, are also involved in the regulation of stomatal aperture in maize, indicating that PIF-mediated regulation of stomatal aperture may be conserved in the plant lineage. Our findings explain the molecular mechanism by which PIFs play a role in red-light-mediated stomatal opening, and demonstrate that PIFs regulate stomatal aperture by coordinating the red light and ABA signaling pathways."
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