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Authors: Xuan Chen, Wei Jiang, Tao Tong, Guang Chen, Fanrong Zeng, Sunghoon Jang, Wei Gao, Zhen Li, Michelle Mak, Fenglin Deng and Zhong-Hua Chen.
Frontiers in Plant Science (2021)
Abstract: "An increase in environmental pollution resulting from toxic heavy metals and metalloids [e.g., cadmium (Cd), arsenic (As), and lead (Pb)] causes serious health risks to humans and animals. Mitigation strategies need to be developed to reduce the accumulation of the toxic elements in plant-derived foods. Natural and genetically-engineered plants with hyper-tolerant and hyper-accumulating capacity of toxic minerals are valuable for phytoremediation. However, the molecular mechanisms of detoxification and accumulation in plants have only been demonstrated in very few plant species such as Arabidopsis and rice. Here, we review the physiological and molecular aspects of jasmonic acid and the jasmonate derivatives (JAs) in response to toxic heavy metals and metalloids. Jasmonates have been identified in, limiting the accumulation and enhancing the tolerance to the toxic elements, by coordinating the ion transport system, the activity of antioxidant enzymes, and the chelating capacity in plants. We also propose the potential involvement of Ca2+ signaling in the stress-induced production of jasmonates. Comparative transcriptomics analyses using the public datasets reveal the key gene families involved in the JA-responsive routes. Furthermore, we show that JAs may function as a fundamental phytohormone that protects plants from heavy metals and metalloids as demonstrated by the evolutionary conservation and diversity of these gene families in a large number of species of the major green plant lineages. Using ATP-Binding Cassette G (ABCG) transporter subfamily of six representative green plant species, we propose that JA transporters in Subgroup 4 of ABCGs may also have roles in heavy metal detoxification. Our paper may provide guidance toward the selection and development of suitable plant and crop species that are tolerant to toxic heavy metals and metalloids."
Authors: Yanlin Liu, Xiaoli Duan, Xiaodi Zhao, Wenlong Ding, Yaowei Wang and Yan Xiong.
Developmental Cell (2021)
Editor's view: Amino acids (AAs) are key nitrogen-containing upstream signals for mammalian TOR activation. Autotrophic plants absorb and convert inorganic nitrogen into AAs. Liu et al. reveal that nitrate, ammonium, and AAs function as separate signals to stimulate the small GTPase ROP2 for TOR activation in Arabidopsis, independent of the nitrogen-assimilation pathway.
Highlights: • Nitrogen is essential for TOR-promoted true leaf growth • NO3−, NH4+, and Gln function as separate upstream signals to activate TOR • AAs generated from plant-specific pathways have the highest potency to activate TOR • NO3−, NH4+, and Gln all stimulate ROP2 to activate TOR
Abstract: "The evolutionarily conserved target-of-rapamycin (TOR) kinase coordinates cellular and organismal growth in all eukaryotes. Amino acids (AAs) are key upstream signals for mammalian TOR activation, but how nitrogen-related nutrients regulate TOR signaling in plants is poorly understood. Here, we discovered that, independent of nitrogen assimilation, nitrate and ammonium function as primary nitrogen signals to activate TOR in the Arabidopsis leaf primordium. We further identified that a total of 15 proteinogenic AAs are also able to activate TOR, and the first AAs generated from plant specific nitrogen assimilation (glutamine), sulfur assimilation (cysteine), and glycolate cycle (glycine), exhibit the highest potency. Interestingly, nitrate, ammonium, and glutamine all activate the small GTPase Rho-related protein from plants 2 (ROP2), and constitutively active ROP2 restores TOR activation under nitrogen-starvation conditions. Our findings suggest that specific evolutionary adaptations of the nitrogen-TOR signaling pathway occurred in plant lineages, and ROP2 can integrate diverse nitrogen and hormone signals for plant TOR activation."
Authors: Pierre-Mathieu Pélissier, Hans Motte and Tom Beeckman.
Plant Physiology (2021)
One-sentence summary: The impact of nutrients, with a particular focus on nitrate and ammonium, on the different steps of lateral root development is reviewed.
Abstract: "Lateral roots are important to forage for nutrients due to their ability to increase the uptake area of a root system. Hence, it comes as no surprise that lateral root formation is affected by nutrients or nutrient starvation, and as such contributes to the root system plasticity. Understanding the molecular mechanisms regulating root adaptation dynamics towards nutrient availability is useful to optimize plant nutrient use efficiency. There is at present a profound, though still evolving, knowledge on lateral root pathways. Here, we aimed to review the intersection with nutrient signaling pathways to give an update on the regulation of lateral root development by nutrients, with a particular focus on nitrogen. Remarkably, it is for most nutrients not clear how lateral root formation is controlled. Only for nitrogen, one of the most dominant nutrients in the control of lateral root formation, the crosstalk with multiple key signals determining lateral root development is clearly shown. In this update, we first present a general overview of the current knowledge of how nutrients affect lateral root formation, followed by a deeper discussion on how nitrogen signaling pathways act on different lateral root-mediating mechanisms for which multiple recent studies yield insights."
Authors: Yun-Shil Gho, Min-Yeong Song, Do-Young Bae, Heebak Choi and Ki-Hong Jung.
International Journal of Molecular Sciences (2021)
Abstract: "Auxins play an essential role in regulating plant growth and adaptation to abiotic stresses, such as nutrient stress. Our current understanding of auxins is based almost entirely on the results of research on the eudicot Arabidopsis thaliana, however, the role of the rice PIN-FORMED (PIN) auxin efflux carriers in the regulation of the ammonium-dependent response remains elusive. Here, we analyzed the expression patterns in various organs/tissues and the ammonium-dependent response of rice PIN-family genes (OsPIN genes) via qRT–PCR, and attempted to elucidate the relationship between nitrogen (N) utilization and auxin transporters. To investigate auxin distribution under ammonium-dependent response after N deficiency in rice roots, we used DR5::VENUS reporter lines that retained a highly active synthetic auxin response. Subsequently, we confirmed that ammonium supplementation reduced the DR5::VENUS signal compared with that observed in the N-deficient condition. These results are consistent with the decreased expression patterns of almost all OsPIN genes in the presence of the ammonium-dependent response to N deficiency. Furthermore, the ospin1b mutant showed an insensitive phenotype in the ammonium-dependent response to N deficiency and disturbances in the regulation of several N-assimilation genes. These molecular and physiological findings suggest that auxin is involved in the ammonium assimilation process of rice, which is a model crop plant."
Authors: Snigdha Rai, Prashant Kumar Singh, Samriti Mankotia, Jagannath Swain and Santosh B. Satbhai.
Plant Stress (2021)
Highlights: • Micronutrients are vital for plant growth and development. • The optimal concentration of each element is critical. However, in excess it affects normal physiology of the plant. • Iron is the third most limiting nutrient. • Hormones and small molecules affect Fe uptake. • Crosstalk between different nutrients are poorly understood.
Abstract: "Micronutrients like copper (Cu), manganese (Mn), Iron (Fe), and Zinc (Zn) are essential for plants, and their functions are tightly linked for vital metabolism. The normal concentration range for each of these metals in the plant is narrow, with both deficiencies and excesses causing severe physiological implications. Maintaining an optimum level of these redox-active metals in the plant requires balanced activities of transporters that mediate import into the cell, proper distribution to where it is needed and storage, and use in metalloproteins and metalloenzymes within the cell. Understanding the complexities of interaction between Fe and other micronutrients and how it defines the health of the plants would facilitate improved plant growth strategies on soils with the low/high levels of these metals, with implications for agriculture and phytoremediation. The review briefly discusses the role of these metals in plant and expands on iron homeostasis and its crosstalk with Cu, Zn, and Mn."
Authors: Mohammad Golam Mostofa, Md. Mezanur Rahman, Kien Huu Nguyen, Weiqiang Li, Yasuko Watanabe, Cuong Duy Tran, Minghui Zhang, Misao Itouga, Masayuki Fujita, Lam-Son Phan Tran.
Journal of Hazardous Materials (2021)
Highlights: • Strigolactones (SLs)’ mechanisms underpinning arsenic-stress tolerance in rice are unknown. • SL-deficient d10 and d17 rice mutants accumulated higher amount of arsenic in roots than WT. • SL deficiency increased oxidative stress and membrane damage in arsenate-treated d10 and d17 roots. • SL-functions in arsenate-stress tolerance are linked to GSH-assisted vacuolar-sequestration of arsenic in roots. • WT roots maintained better redox status and antioxidant system than d10 and d17 roots under arsenate-stress.
Abstract: "We explored genetic evidence for strigolactones’ role in rice tolerance to arsenate-stress. Comparative analyses of roots of wild-type (WT) and strigolactone-deficient mutants d10 and d17 in response to sodium arsenate (Na2AsO4) revealed differential growth inhibition [WT (11.28%) vs. d10 (19.76%) and d17 (18.03%)], biomass reduction [(WT (33.65%) vs. d10 (74.86%) and d17 (60.65%)] and membrane damage (WT < d10 and d17) at 250 μM Na2AsO4. Microscopic and biochemical analyses showed that roots of WT accumulated lower levels of arsenic and oxidative stress indicators like reactive oxygen species, malondialdehyde and hydrogen peroxide than those of strigolactone-deficient mutants. qRT-PCR data indicated lower expression levels of genes (OsPT1, OsPT2, OsPT4 and OsPT8) encoding phosphate-transporters in WT roots than mutant roots, explaining the decreased arsenate and phosphate uptake by WT roots. Increased levels of glutathione and OsPCS1 and OsABCC1 transcripts indicated an efficient vacuolar-sequestration of arsenic in WT roots. Furthermore, higher activities (transcript levels) of SOD (OsCuZnSOD1 and OsCuZnSOD2), APX (OsAPX1 and OsAPX2) and CAT (OsCATA) corresponded to lower oxidative damage in WT roots compared with strigolactone-mutant roots. Collectively, these results highlight that strigolactones are involved in arsenic-stress mitigation by regulating arsenate-uptake, glutathione-biosynthesis, vacuolar-sequestration of arsenic and antioxidant defense responses in rice roots."
Authors: Nabila M. Gomez Mansur, Liliana B. Pena, Adrián E. Bossio, Dalia M. Lewi, Ailin Y. Beznec, Eduardo Blumwald, Vicent Arbona, Aurelio Gómez‐Cadenas, María P. Benavides and Susana M. Gallego.
Physiologia Plantarum (2021)
Abstract: "Cadmium is one of the most important contaminants and it induces severe plant growth restriction. In this study, we analyzed the metabolic changes associated with root growth restriction caused by cadmium in the early seminal root apex of wheat. Our study included two genotypes: the commercial variety ProINTA Federal (WT) and the PSARK::IPT (IPT) line which exhibit high‐grade yield performance under water deficit. Root tips of seedlings grown for 72 h without or with 10 μM CdCl2 (Cd‐WT and Cd‐IPT) were compared. Root length reduction was more severe in Cd‐WT than Cd‐IPT. Cd decreased superoxide dismutase activity in both lines and increased catalase activity only in the WT. In Cd‐IPT, ascorbate and guaiacol peroxidase activities raised compared to Cd‐WT. The hormonal homeostasis was altered by the metal, with significant decreases in abscisic acid, jasmonic acid, 12‐oxophytodienoic acid, gibberellins GA20 and GA7 levels. Increases in flavonoids and phenylamides were also found. Root growth impairment was not associated with a decrease in expansin (EXP) transcripts. On the contrary, TaEXPB8 expression increased in the WT treated by Cd. Our findings suggest that the line expressing the PSARK::IPT construction increased the homeostatic range to cope with Cd stress, which is visible by a lesser reduction of the root elongation compared to WT plants. The decline of root growth produced by Cd was associated with hormonal imbalance at the root apex level. We hypothesize that activation of phenolic secondary metabolism could enhance antioxidant defenses and contribute to cell wall reinforcement to deal with Cd toxicity."
Authors: Peng Wang, Roxane Snijders, Wouter Kohlen, Jieyu Liu, Ton Bisseling and Erik Limpens.
bioRxiv (2021)
Abstract: "To acquire sufficient mineral nutrients such as phosphate (Pi) from the soil, most plants engage in a symbiosis with arbuscular mycorrhizal (AM) fungi. Attracted by plant-secreted strigolactones, the fungi colonize the roots and form highly-branched hyphal structures called arbuscules inside inner cortex cells. It is essential that the host plant controls the different steps of this interaction to maintain its symbiotic nature. However, how plants sense the amount of Pi obtained from the fungus and how this determines the arbuscule lifetime is far from understood. Here, we show that Medicago truncatula SPX-domain containing proteins SPX1 and SPX3 regulate root phosphate starvation responses as well as fungal colonization and arbuscule degradation. SPX1 and SPX3 are induced upon phosphate starvation but become restricted to arbuscule-containing cells upon establishment of the symbiosis. Under Pi-limiting conditions they facilitate the expression of the strigolactone biosynthesis gene DWARF27, which correlates with increased fungal branching by root exudates and increased root colonization. Later, in the arbuscule-containing cells SPX1 and SPX3 redundantly control the timely degradation of arbuscules. This regulation does not seem to involve direct interactions with known transcriptional regulators of arbuscule degradation. We propose a model where SPX1 and SPX3 control arbuscule degeneration in a Pi-dependent manner via a yet-to-identify negative regulator."
Authors: Huwei Sun, Xiaoli Guo, Xuejiao Qi, Fan Feng, Xiaonan Xie, Yali Zhang and Quanzhi Zhao.
The Plant Journal (2021)
Abstract: "Nitrogen (N) is an essential major nutrient for food crops. Although ammonium (NH4+) is the primary N source of rice, nitrate (NO3‐) can also be absorbed and utilized. Rice responds to NO3‐ application by altering its root morphology, such as root elongation. Strigolactones (SLs) are important modulators of root length. However, the roles of SLs and their downstream genes in NO3‐‐induced root elongation remain unclear. Here, the levels of total N and SL (4‐deoxyorobanchol), and the responses of seminal root (SR) lengths to NH4+ and NO3‐ were investigated in rice plants. NO3‐‐promoted SR elongation, possibly due to short‐term signal perception and long‐term nutrient function. Compared with NH4+ condition, higher SL signalling/levels and less D53 protein were recorded in roots of NO3‐‐treated rice plants. In contrast to wild‐type (WT) plants, SR lengths of d mutants were less responsive to NO3‐ condition, and application of rac‐GR24 (SL analogue) restored SR length in d10 (SL‐biosynthesis mutant) but not in d3,d14 and d53 (SL‐responsive mutants), suggesting that higher SL signalling/levels participated in NO3‐‐induced root elongation. D53 interacted with SPL17, and inhibited SPL17‐mediated transactivation from PIN1b promoter. Mutation of SPL14/17 and PIN1b caused insensitivity of root elongation response to NO3‐ and rac‐GR24 applications. Therefore, we presented that perception of SLs by D14 led to degradation of D53 via the proteasome system, which released the suppression of SPL14/17‐modulated the transcription of PIN1b, and resulted in root elongation under NO3‐ supply."
Authors: Yupu Huang, Sheliang Wang, Lei Shi and Fangsen Xu.
Journal of Experimental Botany (2021)
Abstract: "Boron (B) is an essential micronutrient for plant growth and development. Jasmonic acid (JA) plays pivotal roles in plant growth. However, the underlying molecular mechanism of JA involvement in B-deficiency-induced root growth inhibition is yet to be explored. In this study, we investigated the response of JA to B deficiency and the mechanism of JAR1-dependent JA signaling in root growth inhibition under B deficiency. B deficiency enhanced JA signaling in roots, and root growth inhibition was partially restored by JA biosynthesis inhibition. jar1-1 (jasmonate-resistant 1, JAR1) mutant, mutants of coronatine-insensitive 1 (coi1-2) and myc2 defective in JA signaling showed insensitivity to B deficiency. Ethylene-overproduction mutant eto1 and ethylene-insensitive mutant etr1 showed sensitivity and insensitivity to B deficiency, respectively, suggesting that ethylene is involved in the inhibition of primary root growth under B deficiency. Furthermore, after a declined in EIN3 protein levels, which may contribute to root growth, ethylene signaling was weakened in the jar1-1 mutant root under B deficiency. Under B deficiency, B concentrations were increased in the roots and shoots of the jar1-1 mutant, owing to the large root system and its activity. Therefore, our findings revealed that JA, which is involved in the inhibition of root growth under B deficiency, is regulated by JAR1 activated JA and ethylene signaling pathways."
Authors: Laura Ravazzolo, Stéphanie Boutet-Mercey, François Perreau, Cristian Forestan, Serena Varotto, Benedetto Ruperti and Silvia Quaggiotti.
Plant and Cell Physiology (2021)
Abstract: "In maize, nitrate regulates root development thanks to the coordinated action of many players. In this study, the involvement of SLs and auxin as putative components of the nitrate regulation of lateral root was investigated. To this aim, the endogenous SL content of maize root in response to nitrate was assessed by LC-MS/MS and measurements of lateral root density in the presence of analogues or inhibitors of auxin and strigolactones were performed. Furthermore, an untargeted RNA-seq based approach was used to better characterize the participation of auxin and strigolactones to the transcriptional signature of maize root response to nitrate. Our results suggested that N deprivation induces zealactone and carlactonoic acid biosynthesis in root, to a higher extent if compared to P-deprived roots. Moreover, data on lateral root density led to hypothesise that the induction of LR development early occurring upon nitrate supply involves the inhibition of SL biosynthesis, but that the downstream target of SL shutdown, beside auxin, includes also additional unknown players. Furthermore, RNA-seq results provided a set of putative markers for the auxin- or SL-dependent action of nitrate, meanwhile allowing to identify also novel components of the molecular regulation of maize root response to nitrate. Globally the existence of at least four different pathways was hypothesised, one dependent on auxin, a second one mediated by SLs, a third deriving from the SL-auxin interplay and one last attributable to nitrate itself through further downstream signals. Further work will be necessary to better assess the reliability of the model proposed."
Authors: Cheng-Wei Qiu, Can Zhang, Nian-Hong Wang, Weihua Mao and Feibo Wu.
Environmental Pollution (2021)
Highlights: • External strigolactone GR24 significantly alleviates Cd-toxicity in barley. • GR24 reduced Cd content, improved photosynthesis performance and uptake of Zn, Cu, Mn and Fe. • GR24 alleviated Cd-induced oxidative stress, induced AsA/GSH, and activities of AsA-GSH cycle. • GR24 mitigated the Cd-induced depression of NO and NOS in Cd-sensitive genotype. • NO and AsA-GSH cycle involved in GR24-induced Cd tolerance in barley.
Abstract: "Cadmium (Cd) in the food chain poses a serious hazard to human health. Therefore, a greenhouse hydroponic experiment was conducted to examine the potential of exogenously strigolactone GR24 in lessening Cd toxicity and to investigate its physiological mechanisms in the two barley genotypes, W6nk2 (Cd-sensitive) and Zhenong8 (Cd-tolerant). Exogenous application of 1 μM GR24 (strigol analogue) reduced the suppression of growth caused by 10 μM Cd, lowered plant Cd contents, increased the contents of other nutrient elements, protected chlorophyll, sustained photosynthesis, and markedly reduced Cd-induced H2O2 and malondialdehyde accumulation in barley. Furthermore, exogenous GR24 markedly increased NO contents and nitric oxide synthase activity in the Cd-sensitive genotype, W6nk2, effectively alleviating the Cd-induced repression of the activities of superoxide dismutase and peroxidase, increasing reduced glutathione (GSH) and ascorbic acid (AsA) pools and activities of AsA-GSH cycle including ascorbate peroxidase, glutathione peroxidase, glutathione reductase, dehydroascorbate reductase and monodehydroascorbate reductase. The findings of the present study indicate that GR24 could be a candidate for Cd detoxification by decreasing Cd contents, balancing nutrient elements, and protecting barley plants from toxic oxidation via indirectly eliminating reactive oxygen species (ROS), consequently contributing to reducing the potential risk of Cd pollution."
Authors: Tianli Tu, Shuangshuang Zheng, Panrong Ren, Xianwen Meng, Jiuhai Zhao, Qian Chen and Chuanyou Li.
Plant Physiology (2021)
Abstract: "Interactions between plant hormones and environmental signals are important for the maintenance of root growth plasticity under ever-changing environmental conditions. Here, we demonstrate that arsenate (AsV), the most prevalent form of arsenic (As) in nature, restrains elongation of the primary root through transcriptional regulation of local auxin biosynthesis genes in the root tips of Arabidopsis (Arabidopsis thaliana) plants. The ANTHRANILATE SYNTHASE ALPHA SUBUNIT 1 (ASA1) and BETA SUBUNIT 1 (ASB1) genes encode enzymes that catalyze the conversion of chorismate to anthranilate (ANT) via the tryptophan-dependent auxin biosynthesis pathway. Our results showed that AsV upregulates ASA1 and ASB1 expression in root tips, and ASA1- and ASB1-mediated auxin biosynthesis is involved in AsV-induced root growth inhibition. Further investigation confirmed that AsV activates cytokinin signaling by stabilizing the type-B ARABIDOPSIS RESPONSE REGULATOR1 (ARR1) protein, which directly promotes the transcription of ASA1 and ASB1 genes by binding to their promoters. Genetic analysis revealed that ASA1 and ASB1 are epistatic to ARR1 in the AsV-induced inhibition of primary root elongation. Overall, the results of this study illustrate a molecular framework that explains AsV-induced root growth inhibition via crosstalk between two major plant growth regulators, auxin and cytokinin."
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Authors: Fanmiao Wang, Hideki Yoshida and Makoto Matsuoka.
Plant and Cell Physiology (2021)
Abstract: "Traditional breeding for high-yielding crops has mainly relied on the widespread cultivation of gibberellin (GA)-deficient semi-dwarf varieties, as dwarfism increases lodging resistance and allows for high nitrogen use, resulting in high grain yield. Although the adoption of semi-dwarf varieties in rice and wheat breeding brought big success to the “Green Revolution” in the 20th century, it consequently increased the demand for nitrogen-based fertilizer, which causes severe threat to ecosystems and sustainable agriculture. In order to make the “Green Revolution” truly green, it is necessary to develop new varieties with high nitrogen-use efficiency (NUE). Under this demand, research on NUE, mainly for rice, has made great strides in the last decade. This mini-review focuses on three aspects of recent epoch-making findings on rice breeding for high NUE. The first one on “NUE genes related to GA signaling” shows how promising it is to improve NUE in semi-dwarf Green Revolution Varieties. The second aspect centers around the nitrate transporter1.1B, NRT1.1B; studies have revealed a nutrient signaling pathway through the discovery of the nitrate-NRT1.1B-SPX4-NLP3 cascade. The last one is based on the recent finding that the Teosinte branched1, Cycloidea, Proliferating cell factor (TCP)-domain protein 19 underlies the genomic basis of geographical adaptation to soil nitrogen; OsTCP19 regulates the expression of a key transacting factor, DLT/SMOS2, which participates in the signaling of four different phytohormones, GA, auxin, brassinosteroid and strigolactone. Collectively, these breakthrough findings represent a significant step towards breeding high NUE rice in the future."
Authors: Poonam Kanwar, Dibin Baby and Petra Bauer.
Plant Biology (2021)
Abstract: "Osmotic stresses like salinity and drought have deleterious effects on uptake and translocation of essential mineral nutrients. Iron (Fe) is an important micronutrient that regulates many processes in plants. Plants have adopted various molecular and physiological strategies for Fe acquisition from soil and transport to and within plants. Dynamic Fe signaling in plants tightly regulates iron uptake and homeostasis. This way, Fe nutrition is adjusted to growth and stress conditions, and Fe deficiency‐regulated transcription factors such as FER‐LIKE IRON DEFICIENCY‐INDUCED TRANSCRIPTION FACTOR (FIT) act as regulatory hubs in these responses. Here, we review and analyze the expression of the various components of the Fe signaling during osmotic stresses. We discuss common players in the Fe and osmotic stress signaling. Furthermore, this review focuses on exploring a novel and exciting direct connection of regulatory mechanisms of Fe intake and acquisition with ABA‐mediated environmental stress cues like salt/drought. We propose a model how environmental stress affects Fe uptake and acquisition and vice versa at molecular‐physiological level in plants."
Authors: Yi-Ran Ren, Qiang Zhao, Yu-Ying Yang, Rui Zhang, Xiao-Fei Wang, Tian-En Zhang, Chun-Xiang You, He-Qiang Huo and Yu-Jin Hao.
Plant Physiology (2021)
One-sentence summary: The BTB-TAZ protein interacts with and promotes ubiquitination and degradation of DELLA protein, thus regulating plant growth in response to nitrate.
Abstract: "Nitrate acts as a vital signal molecule in the modulation of plant growth and development. The phytohormones gibberellin (GA) is also involved in this process. However, the exact molecular mechanism of how nitrate and GA signaling pathway work together in regulating plant growth remains poorly understood. In this study, we found that a nitrate-responsive BTB/TAZ protein MdBT2 participates in regulating nitrate-induced plant growth in apple (Malus × domestica). Yeast two-hybridization, protein pull-down, and bimolecular fluorescence complementation (BiFC) assays showed that MdBT2 interacts with a DELLA protein MdRGL3a, which is required for the ubiquitination and degradation of MdRGL3a proteins via a 26S proteasome-dependent pathway. Furthermore, heterologous expression of MdBT2 partially rescued growth inhibition caused by overexpression of MdRGL3a in Arabidopsis. Taken together, our findings indicate that MdBT2 promotes nitrate-induced plant growth partially through reducing the abundance of the DELLA protein MdRGL3a."
Authors: Daisuke Takagi, Keiki Ishiyama, Mao Suganami, Tomokazu Ushijima, Takeshi Fujii, Youshi Tazoe, Michio Kawasaki, Ko Noguchi and Amane Makino.
bioRxiv (2021)
Abstract: "Despite the essentiality of Mn in terrestrial plants, its excessive accumulation in plant tissues causes growth defects, known as Mn toxicity. Mn toxicity can be divided into apoplastic and symplastic types depending on its onset. For growth defects, symplastic rather than apoplastic Mn toxicity is hypothesised to be more critical. However, details of the relationship between growth defects and symplastic Mn toxicity remains elusive. In this study, we aimed to elucidate the molecular mechanisms of symplastic Mn toxicity in rice plants. We found that under excess Mn conditions, CO2 assimilation was inhibited by stomatal closure, and both carbon anabolic and catabolic activities were decreased. In addition to stomatal dysfunction, stomatal and leaf anatomical development were also altered by excess Mn accumulation. Furthermore, the indole acetic acid (IAA) concentration was decreased, and auxin-responsive gene expression analyses showed IAA-deficient symptoms in leaves due to excess Mn accumulation. These results suggest that excessive Mn accumulation causes IAA deficiency, and low IAA concentrations suppress plant growth by suppressing stomatal opening and leaf anatomical development for efficient CO2 assimilation in leaves."
Authors: Liaoliao Ye, Peizhi Yang, Yinwei Zeng, Chun Li, Ni Jian, Ruihua Wang, Siyuan Huang, Rongchen Yang, Long Wei, Haiyan Zhao, Qingsong Zheng, Huiling Gao and Jinlong Liu.
Journal of Hazardous Materials (2021)
Highlights: • Appropriate rhizobia strains are essential to reduce As accumulation in legumes. • As accumulation in plants can be decreased by nitrogen and NRT3.1 mutation. • The contents of As negatively correlated with nitrogen levels in Rhizobium symbionts. • ABA and linalool can regulate the accumulation of As in plants. • Rhizobia symbiosis modulates As accumulation via NRT3.1 regulated by ABA and linalool.
Abstract: "Arsenic (As) contamination is a worldwide problem and threatens human health. Here, we found that Rhizobium symbiosis can improve the tolerance to arsenate [As(V)], and a wild type R. meliloti Rm5038 symbiosis can significantly decrease the accumulation of As in Medicago truncatula shoots. The As content in plants could be decreased by nitrogen and the mutation of nitrate transporter NRT3.1. The expression of M. truncatula NRT3.1-like gene NRT3.1L1 could reverse the As(V)-tolerance phenotype of the Arabidopsis nrt3.1 mutant. Rm5038 symbiosis significantly increased the level of nitrogen in the shoot and reduced the expression of NRT3.1Ls in plants afflicted by As(V). The genetic analyses of aba2–1, pyr1/pyl1/2/4/5/8, and abi1–2/abi2–2/hab1–1/pp2ca-1 mutants revealed that abscisic acid (ABA) signaling regulates the tolerance of plants to As(V). ABA and linalool could promote the expression of NRT3.1Ls, however, their root biosynthesis was inhibited by ammonium, the first form of nitrogen fixed by Rhizobium symbiosis. Moreover, ABA and linalool may also control As and nitrate accumulation in Rhizobium symbionts via signaling pathways other than ammonia and NRT3.1Ls. Thus, Rhizobium symbiosis modulates the accumulation of As in plants via nitrogen and NRT3.1Ls regulated by ABA and linalool, which provides novel approaches to reduce As accumulation in legume crops."
Authors: Fanny Bellegarde and Hitoshi Sakakibara.
Plant and Cell Physiology (2021)
Excerpts: "In this issue, Ravazzolo et al. (2021) sought to investigate the putative interaction between SL and the auxin pathway for LR development in response to nitrate availability in maize. They first analyzed how nitrate starvation impacts SL concentration in the roots. They showed that nitrogen-deficiency strongly induced SL biosynthesis, especially zealactone (already demonstrated in the exudate) and its precursor carlactonoic acid. To obtain insight into the role of SL in LR initiation under different nitrate conditions, they analyzed the effect of either an analog or inhibitor of auxin and SL on lateral root density (Fig. 1) and expression of ZmCCD8 and ZmWBC33, and showed that repression of the ZmCCD8 by nitrate provision is auxin-independent while the repression of both ZmWBC33 and SL exudation appears to be auxin-dependent."
"By comparing diverse treatments and conditions (either alone or in combination), Ravazzolo et al. (2021) have deepened our knowledge of SL regulation by nitrate variation and provide new evidence for SL and auxin crosstalk in nitrate-dependent RSA regulation. Although the molecular link between SL and auxin in LR formation is still unclear, the identification of novel markers permitting distinction of the four independent pathways should prove to be useful tools in future investigations."
Authors: Jorge J. Casal and José M. Estevez.
Cold Spring Harbor Perspectives in Biology (2021)
Abstract: "Plant fitness depends on the adequate morphological adjustment to the prevailing conditions of the environment. Therefore, plants sense environmental cues through their life cycle, including the presence of full darkness, light, or shade, the range of ambient temperatures, the direction of light and gravity vectors, and the presence of water and mineral nutrients (such as nitrate and phosphate) in the soil. The environmental information impinges on different aspects of the auxin system such as auxin synthesis, degradation, transport, perception, and downstream transcriptional regulation to modulate organ growth. Although a single environmental cue can affect several of these points, the relative impacts differ significantly among the various growth processes and cues. While stability in the generation of precise auxin gradients serves to guide the basic developmental pattern, dynamic changes in the auxin system fine-tune body shape to optimize the capture of environmental resources."
Authors: Mengmeng Hou, Daxia Wu, Ying Li, Wenqing Tao, Ling Chao and Yali Zhang.
Plant Signaling & Behavior (2021)
Abstract: "Shoot branching is determined by axillary bud formation and outgrowth and remains one of the most variable determinants of yield in many crops. Plant nitrogen (N) acquired mainly in the forms of nitrate and ammonium from soil, dominates plant development, and high-yield crop production relies heavily on N fertilization. In this review, the regulation of axillary bud outgrowth by N availability and forms is summarized in plant species. The mechanisms of auxin function in this process have been well characterized and reviewed, while recent literature has highlighted that auxin export from a bud plays a critical role in N-modulating this process."
Authors: Pascal Ganz, Romano Porras-Murillo, Toyosi Ijato, Jochen Menz, Tatsiana Straub, Nils Stührwohldt, Narges Moradtalab, Uwe Ludewig and Benjamin Neuhäuser.
bioRxiv (2021)
Abstract: "Ammonium uptake at plant roots is regulated at the transcriptional, post-transcriptional and post-translational levels. Phosphorylation by the protein kinase CIPK23 transiently inactivates the ammonium transporters (AMT1s) but the phosphatases activating AMT1s remain unknown. Here, we have identified the PP2C phosphatase ABI1 as an activator of AMTs in Arabidopsis thaliana. We show that high external ammonium concentrations elevate the stress phytohormone abscisic acid (ABA) by de-glycosylation. Active ABA is sensed by ABI1-PYL complexes followed by the inactivation of ABI1 activating CIPK23. Under favourable growth conditions, ABI1 reduces AMT1 phosphorylation, both by binding and inactivating CIPK23, and by the direct dephosphorylation of AMT1s. Thus, ABI1 is a positive regulator of ammonium uptake, coupling nutrient acquisition to abiotic stress signalling. Elevated ABA reduces ammonium uptake during stress situations, such as ammonium toxicity, whereas ABI1 reactivates AMT1s under favourable growth conditions."
Authors: Masato Shindo, Seiji Nagasaka, Shosaku Kashiwada, Koichiro Shimomura and Mikihisa Umehara.
Plant Signaling & Behavior (2021)
Abstract: "Strigolactones (SLs) are a class of plant hormones that control plant architecture. SL levels in roots are determined by the nutrient conditions in the rhizosphere, especially the levels of nitrogen (N) and phosphorus (P). Our previous research showed that SL production is induced in response to deficiency of sulfur (S) as well as of N and P, and inhibits shoot branching, accelerates leaf senescence, and regulates lamina joint angle in rice. Here we show biomass, total S contents, and SL levels in rice under S-sufficient and S-deficient conditions using a split-root system. When one part of the root system was cultured in S-sufficient medium and the other in S-deficient medium (+S/−S), shoot fresh weight was unaffected relative to the +S/+S condition. The shoot weight significantly decreased in −S/−S condition. In contrast, there was no significant difference in root fresh weight between +S and −S conditions. In +S/−S condition, SL levels were systemically reduced in both parts, the shoot S content increased, but the root S content in S-deficient medium was unaffected relative to the −S/−S condition. These results suggest that shoots, not roots, recognize S deficiency, which induces SL production in roots."
Authors: Ravi Ramesh Pathak, Vikas Kumar Mandal, Annie Prasanna Jangam, Narendra Sharma, Bhumika Madan, Dinesh Kumar Jaiswal and Nandula Raghuram.
Scientific Reports (2021)
Abstract: "G-proteins are implicated in plant productivity, but their genome-wide roles in regulating agronomically important traits remain uncharacterized. Transcriptomic analyses of rice G-protein alpha subunit mutant (rga1) revealed 2270 differentially expressed genes (DEGs) including those involved in C/N and lipid metabolism, cell wall, hormones and stress. Many DEGs were associated with root, leaf, culm, inflorescence, panicle, grain yield and heading date. The mutant performed better in total weight of filled grains, ratio of filled to unfilled grains and tillers per plant. Protein–protein interaction (PPI) network analysis using experimentally validated interactors revealed many RGA1-responsive genes involved in tiller development. qPCR validated the differential expression of genes involved in strigolactone-mediated tiller formation and grain development. Further, the mutant growth and biomass were unaffected by submergence indicating its role in submergence response. Transcription factor network analysis revealed the importance of RGA1 in nitrogen signaling with DEGs such as Nin-like, WRKY, NAC, bHLH families, nitrite reductase, glutamine synthetase, OsCIPK23 and urea transporter. Sub-clustering of DEGs-associated PPI network revealed that RGA1 regulates metabolism, stress and gene regulation among others. Predicted rice G-protein networks mapped DEGs and revealed potential effectors. Thus, this study expands the roles of RGA1 to agronomically important traits and reveals their underlying processes."
Authors: Camilla Betti, Federica Della Rovere, Diego Piacentini, Laura Fattorini, Giuseppina Falasca and Maria Maddalena Altamura.
Biomolecules (2021)
Abstract: "Developmental and environmental signaling networks often converge during plant growth in response to changing conditions. Stress-induced hormones, such as jasmonates (JAs), can influence growth by crosstalk with other signals like brassinosteroids (BRs) and ethylene (ET). Nevertheless, it is unclear how avoidance of an abiotic stress triggers local changes in development as a response. It is known that stress hormones like JAs/ET and BRs can regulate the division rate of cells from the first asymmetric cell divisions (ACDs) in meristems, suggesting that stem cell activation may take part in developmental changes as a stress-avoidance-induced response. The root system is a prime responder to stress conditions in soil. Together with the primary root and lateral roots (LRs), adventitious roots (ARs) are necessary for survival in numerous plant species. AR and LR formation is affected by soil pollution, causing substantial root architecture changes by either depressing or enhancing rooting as a stress avoidance/survival response. Here, a detailed overview of the crosstalk between JAs, ET, BRs, and the stress mediator nitric oxide (NO) in auxin-induced AR and LR formation, with/without cadmium and arsenic, is presented. Interactions essential in achieving a balance between growth and adaptation to Cd and As soil pollution to ensure survival are reviewed here in the model species Arabidopsis and rice."
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