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Authors: Wanmin Wang, Zizhao Xie, Yuanyuan Wu, Ying Sun, Chenghang Zhan, Liang Jin and Junli Huang.
Environmental and Experimental Botany (2024)
Highlights: • OsJAZ6 modulates rice tillering and drought response by integrating JA with GA signaling. • OsJAZ6 controls the tiller bud growth but not formation. • OsJAZ6 interacts with SLR1 to promote its degradation, which further destabilizes MOC1. • OsJAZ6 and SLR1 have opposite functions in regulating rice tiller bud growth and drought tolerance.
Abstract: "Jasmonic acid (JA) plays crucial functions during plant growth and stress response, but its roles and regulatory mechanism in plant branching remain largely unknown. Rice basal branching (tillering) is an essential agronomic trait that affects crop production. Here, we report that OsJAZ6, the repressor of JA signaling, negatively modulates rice tillering and drought stress tolerance. Loss-of-function mutants of OsJAZ6 exhibit a significant increase in tiller number, while OsJAZ6ΔJas-overexpression lines produce fewer tillers than wild-type plants. Further investigations show that function loss of OsJAZ6 promotes the tiller bud growth rather than formation. Mechanistic studies show that OsJAZ6 interacts with rice DELLA/SLR1 (SLENDER RICE 1), a transcription repressor of gibberellin (GA) signaling, and the interaction promotes SLR1 degradation, which further facilitates the degradation of rice tillering regulator MOC1 (MONOCULM 1), thereby inhibiting the tiller bud growth. In agreement, the slr1 mutant exhibits fewer tillers than wild type. Consistently, application of JA promotes the growth of tiller bud and thus increases the tiller number, while GA treatment results in opposite result. Meanwhile, osjaz6 mutants display enhanced drought tolerance, coupled with increased JA sensitivity, while the slr1 mutant shows the reverse behavior. Collectively, our data demonstrate that OsJAZ6 negatively modulates rice tillering as well as drought stress tolerance by destabilizing SLR1 protein. Our data shed light on the regulatory mechanism of controlling the tiller development and drought stress response in rice by the JA-OsJAZ6-SLR1 module."
Authors: Guoling Guo, Haiyan Zhang, Weiyu Dong, Bo Xu, Youyu Wang, Qingchen Zhao, Lun Liu, Xiaomei Tang, Li Liu, Zhenfeng Ye, Wei Heng, Liwu Zhu and Bing Jia.
Journal of Integrative Agriculture (2024)
Abstract: "Drought stress represents a devastating natural disaster driven by the continuing intensification of global warming, which seriously threats the productivity and quality of several horticultural crops, including pear. Gibberellins (GAs) play crucial roles in plant growth, development, and responses to drought stress. Previous studies have shown significant reductions of GA levels in plants under drought stress; however, understanding of the intrinsic regulation mechanisms of GA-mediated drought stress in pear remains very limited. Here, we show that drought stress could impair the accumulation of bioactive GAs (BGAs), and subsequently identified PbrGA2ox1 as a chloroplast-localized GA deactivation gene, which was significantly induced by drought stress and abscisic acid (ABA) treatment, but was suppressed by GA3 treatment. PbrGA2ox1-overexpressing transgenic tobacco (Nicotiana benthamiana) plants exhibited enhanced tolerance to dehydration and drought stresses, whereas knock-down of PbrGA2ox1 in pear (Pyrus betulaefolia) by virus-induced gene silencing lead to elevated drought sensitivity. Transgenic plants were hypersensitive to ABA, and had a lower BGAs content, enhanced reactive oxygen species (ROS) scavenging ability, and augmented ABA accumulation and signaling under drought stress compared to wild-type plants. However, the opposite effects were observed with PbrGA2ox1 silencing in pear. Moreover, exogenous GA3 treatment aggravated the ROS toxification effect and restrained ABA synthesis and signaling, resulting in the compromised drought tolerance of pear. In summary, our results shed light on the mechanism by which BGAs are eliminated in pear leaves under drought stress, providing a further insight into the mechanism regulating the effects of the GA on the drought tolerance of plants."
Authors: Qin Song, Lingfei Kong, Jiarui Yang, Minghui Lin, Yuqian Zhang, Xuerui Yang, Xiaojing Wang, Zhengjie Zhao, Meng Zhang, Jiarui Pan, Shunqin Zhu, Bo Jiao, Changzheng Xu and Keming Luo.
The Plant Journal (2024)
Abstract: "Drought stress caused by global warming has resulted in significant tree mortality, driving the evolution of water conservation strategies in trees. Although phytohormones have been implicated in morphological adaptations to water deficits, the molecular mechanisms underlying these processes in woody plants remain unclear. Here, we report that overexpression of PtoMYB142 in Populus tomentosa results in a dwarfism phenotype with reduced leaf cell size, vessel lumen area, and vessel density in the stem xylem, leading to significantly enhanced drought resistance. We found that PtoMYB142 modulates gibberellin catabolism in response to drought stress by binding directly to the promoter of PtoGA2ox4, a GA2-oxidase gene induced under drought stress. Conversely, knockout of PtoMYB142 by the CRISPR/Cas9 system reduced drought resistance. Our results show that the reduced leaf size and vessel area, as well as the increased vessel density, improve leaf relative water content and stem water potential under drought stress. Furthermore, exogenous GA3 application rescued GA-deficient phenotypes in PtoMYB142-overexpressing plants and reversed their drought resistance. By suppressing the expression of PtoGA2ox4, the manifestation of GA-deficient characteristics, as well as the conferred resistance to drought in PtoMYB142-overexpressing poplars, was impeded. Our study provides insights into the molecular mechanisms underlying tree drought resistance, potentially offering novel transgenic strategies to enhance tree resistance to drought."
Authors: XiangGuo Liu, Yang Liu, Ziqi Chen, Chuang Zhang, Jia Guo, Qing Liu, Yuejia Yin, Yang Hu, Hanchao Xia, Bingyang Li, Xiaopeng Sun and Yidan Li.
Research Square (2023)
Abstract: "Drought stress, a major plant abiotic stress, is capable of suppressing crop yield performance severely. However, the trade-off between crop drought tolerance and yield performance turns out to be significantly challenging in drought-resistant crop breeding. Several phytohormones (e.g., gibberellin (GA)) have been reported to play a certain role in plant drought response, which also take on critical significance in plant growth and development. In this study, the loss-of-function mutations of GA biosynthesis enzyme ZmGA20ox3 were produced using the CRISPR-Cas9 system in maize. As indicated by the result of two-year field trials, the above-mentioned mutants displayed semi-dwarfing phenotype with the decrease of GA1, and almost no yield loss was generated compared with wild-type (WT) plants. Interestingly, as revealed by the transcriptome analysis, differential expressed genes (DEGs) were notably enriched in abiotic stress progresses, and biochemical tests indicated the significantly increased ABA, JA, and DIMBOA levels in mutants, suggesting that ZmGA20ox3 may take on vital significance in stress response in maize. The in-depth analysis suggested that the loss function of ZmGA20ox3 can enhance drought tolerance in maize seedling, reduce Anthesis-Silking Interval (ASI) delay while decreasing the yield loss significantly in the field under drought conditions. The results of this study supported that regulating ZmGA20ox3 can improve plant height while enhancing drought resistance in maize, thus serving as a novel method for drought-resistant genetic improvement in maize."
Authors: Xinkai Jin, Yifan Zhang, Xingxing Li and Junli Huang.
The Plant Journal (2023)
Abstract: "The antagonism between gibberellin (GA) and abscisic acid (ABA) signaling pathways is vital to balance plant growth and stress response. Nevertheless, the mechanism by which plants determine the balance remains to be elucidated. Here, we report that rice NUCLEAR FACTOR-Y A3 (OsNF-YA3) modulates GA- and ABA-mediated balance between plant growth and osmotic stress tolerance. OsNF-YA3 loss-of-function mutants exhibit stunted growth, compromised GA biosynthetic gene expression, and decreased GA levels, while its overexpression lines have promoted growth and enhanced GA content. ChIP-qPCR analysis and transient transcriptional regulation assays demonstrate that OsNF-YA3 activates GA biosynthetic gene OsGA20ox1 expression. Furthermore, the DELLA protein SLENDER RICE1 (SLR1) physically interacts with OsNF-YA3 and thus inhibits its transcriptional activity. On the other side, OsNF-YA3 negatively regulates plant osmotic stress tolerance by repressing ABA response. OsNF-YA3 reduces ABA levels by transcriptionally regulating ABA catabolic genes OsABA8ox1 and OsABA8ox3 by binding to their promoters. Furthermore, OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (SAPK9), the positive component in ABA signaling, interacts with OsNF-YA3 and mediates OsNF-YA3 phosphorylation, resulting in its degradation in plants. Collectively, our findings establish OsNF-YA3 as an important transcription factor that positively modulates GA-regulated plant growth and negatively controls ABA-mediated water-deficit and salt tolerance. These findings shed light on the regulatory mechanism underlying the balance between the growth and stress response of the plant."
Authors: Leah R. Band, Hilde Nelissen, Simon P. Preston, Bart Rymen, Els Prinsen, Hamada AbdElgawad and Gerrit T. S. Beemster.
PNAS (2022)
Abstract: "The hormone gibberellin (GA) controls plant growth and regulates growth responses to environmental stress. In monocotyledonous leaves, GA controls growth by regulating division–zone size. We used a systems approach to investigate the establishment of the GA distribution in the maize leaf growth zone to understand how drought and cold alter leaf growth. By developing and parameterizing a multiscale computational model that includes cell movement, growth-induced dilution, and metabolic activities, we revealed that the GA distribution is predominantly determined by variations in GA metabolism. Considering wild-type and UBI::GA20-OX-1 leaves, the model predicted the peak in GA concentration, which has been shown to determine division–zone size. Drought and cold modified enzyme transcript levels, although the model revealed that this did not explain the observed GA distributions. Instead, the model predicted that GA distributions are also mediated by posttranscriptional modifications increasing the activity of GA 20-oxidase in drought and of GA 2-oxidase in cold, which we confirmed by enzyme activity measurements. This work provides a mechanistic understanding of the role of GA metabolism in plant growth regulation.
Authors: M. Agustí, C. Reig, A. Martínez-Fuentes and C. Mesejo.
Frontiers in Plant Science (2022)
Abstract: "Citrus are polycarpic and evergreen species that flower once in spring or several times a year depending on the genotype and the climatic conditions. Floral induction is triggered by low temperature and water-deficit stress and occurs 2–3 months before bud sprouting, whereas differentiation takes place at the same time as sprouting. The induced buds develop single flowers or determinate inflorescences, so that vegetative growth is required at the axillary buds to renew the polycarpic habit. The presence of fruits inhibits sprouting and flower induction from nearby axillary buds in the current season. In some species and cultivars, this results in low flowering intensity the following spring, thus giving rise to alternate bearing. A number of key flowering genes act in the leaf (CiFT3, CcMADS19, etc.) or in the bud (CsLFY, CsTFL1, etc.) to promote or inhibit both flowering time and reproductive meristem identity in response to these climatic factors, the fruit dominance, or the age of the plant (juvenility). The expression of some of these genes can be modified by gibberellin treatments, which reduce bud sprouting and flowering in adult trees, and constitute the main horticultural technique to control flowering in citrus. This review presents a comprehensive view of all aspects of the flowering process in citrus, converging the research published during the past half century, which focused on plant growth regulators and the nutritional source-sink relationships and guided research toward the study of gene transcription and plant transformation, and the advances made with the development of the tools of molecular biology published during the current century."
Authors: Hagai Shohat, Natanella Illouz Eliaz and David Weiss.
Molecular Horticulture (2021)
Abstract: "The growth-promoting hormone gibberellin (GA) regulates numerous developmental processes throughout the plant life cycle. It also affects plant response to biotic and abiotic stresses. GA metabolism and signaling in tomato (Solanum lycopersicum) have been studied in the last three decades and major components of the pathways were characterized. These include major biosynthesis and catabolism enzymes and signaling components, such as the three GA receptors GIBBERELLIN INSENSITIVE DWARF 1 (GID1) and DELLA protein PROCERA (PRO), the central response suppressor. The role of these components in tomato plant development and response to the environment have been investigated. Cultivated tomato, similar to many other crop plants, are susceptible to water deficiency. Numerous studies on tomato response to drought have been conducted, including the possible role of GA in tomato drought resistance. Most studies showed that reduced levels or activity of GA improves drought tolerance and drought avoidance. This review aims to provide an overview on GA biosynthesis and signaling in tomato, how drought affects these pathways and how changes in GA activity affect tomato plant response to water deficiency. It also presents the potential of using the GA pathway to generate drought-tolerant tomato plants with improved performance under both irrigation and water-limited conditions."
Authors: Jie Guo, Xionghui Bai, Keli Dai, Xiangyang Yuan, Pingyi Guo, Meixue Zhou, Weiping Shi and Chenyang Hao.
Frontiers in Plant Science (2021)
Abstract: "GATA transcription factors (TFs) are type IV zinc-finger proteins that have roles in plant development and growth. The 27 GATA TFs identified in the Brachypodium distachyon genome in this study were unevenly distributed across all five chromosomes and classified into four subgroups. Phylogenesis-related GATAs shared similar gene structures and conserved motifs. Expression profiles showed that all BdGATA genes were expressed in leaves and most were induced by PEG treatment. BdGATA13 was predominantly expressed in leaf tissue and phylogenetically close to OsSNFL1, AtGNC, and AtGNL. Its protein was detected in the nucleus by subcellular localization analysis. Overexpression of BdGATA13 in transgenic Arabidopsis resulted in darker green leaves, later flowering, and more importantly, enhanced drought tolerance compared to the wild type. BdGATA13 also promoted primary root development under GA treatment. These results lay a foundation for better understanding the function of GATA genes in B. distachyon and other plants."
Authors: Xueqin Song, Yanqiu Zhao, Jinnan Wang and Meng-Zhu Lu.
Journal of Experimental Botany (2021)
Abstract: "Plant architecture is genetically controlled but is influenced by environmental factors. Plants have evolved adaptive mechanisms that allow changes in their architectures under stress, in which phytohormones play a central role. However, the gene regulators that connect growth and stress signals are rarely reported. Here, we report that a class I KNOX gene, PagKNAT2/6b, can directly inhibit the synthesis of gibberellin (GA), thus altering plant architecture and improving drought resistance in Populus. Expression of PagKNAT2/6b was significantly induced under drought conditions, and transgenic poplars overexpressing PagKNAT2/6b exhibited shorter internode length and smaller leaf size with short or even absent petioles. Interestingly, these transgenic plants showed improved drought resistance under both short- and long-term drought stress. Histological observations indicated that the decreased internode length and leaf size were mainly caused by the inhibition of cell elongation and expansion. GA content was reduced and the GA20-oxidase gene PagGA20ox1 was downregulated in overexpressing plants. Expression of PagGA20ox1 was negatively related to that of PagKNAT2/6b under drought stress. Chromatin immunoprecipitation and transient transcription activity assays revealed that PagGA20ox1 was directly targeted by PagKNAT2/6b. Therefore, this study provides evidence that PagKNAT2/6b mediates stress signals and changes in plant architecture via GA signaling by downregulating PagGA20ox1."
Authors: Jing Xiong, Xuanjun Feng, Weixiao Zhang, Xianqiu Wang, Yue Hu, Xuemei Zhang, Fengkai Wu, Wei Guo, Wubing Xie, Qingjun Wang, Jie Xu and Yanli Lu.
bioRxiv (2021)
Abstract: "Lateral organ boundaries domain (LBD) proteins are plant-specific transcription factors. Class I LBD members are widely reported to be pivotal for organ development, however, the role of class II members is unknown in cereal crops. Class II LBD proteins are distinguished from class I by the lack of a Gly-Ala-Ser (GAS) peptide and leucine-zipper-like coiled-coil domain, which is thought to be essential for protein dimerization. In this study, ZmLBD5 and ZmLBD33 form homo- and hetero-dimers, like class I members. At seedling stage, ZmLBD5 promoted biomass accumulation (shoot dry weight and root dry weight), root development (root length, root number, and root volume), and organ expansion (leaf area), while ZmLBD33 repressed these processes and display a dwarf phenotype. Both ZmLBD5 and ZmLBD33 displayed negative roles in drought tolerance mainly by increasing stomatal density and stomatal aperture. RNA sequencing, gene ontology enrichment analysis, and transient luciferase expression assays indicated that ZmLBD5 and ZmLBD33 are mainly involved in the regulation of the TPS-KS-GA2ox gene module, which comprises key enzymatic genes upstream of GA and ABA biosynthesis. GA1 content increased in ZmLBD5-overexpressing seedlings, while GA3 and abscisic acid content decreased in both transgenic seedlings. Consequently, exogenous GA1 or GA3 undoubtedly rescued the dwarf phenotype of ZmLBD33-overexpressing plants, with GA1 performing better. The study of ZmLBD5 and ZmLBD33 sheds light on the function of the class II LBD gene family in maize."
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Authors: Zhen Liu, Xiao-Feng Cheng, Ying-Ning Zou, Anoop Kumar Srivastava, Mashael Daghash Alqahtani and Qiang-Sheng Wu.
Environmental and Experimental Botany (2024)
Highlights • AMF boosted plant growth as well as POD and CAT activity in roots under drought. • Nine GA species were detected in roots, with GA4 only found in AMF roots. • AMF reduced GA3, but increased GA5, GA9, and GA15 levels under drought. • AMF up-regulated the expression of PtCPS, PtPKS, PtKO, PtGA20ox, PtGA3ox, and PtGA2ox under drought. • AMF increased the expression of the DELLA genes PtGaipb and PtGai under drought.
Abstract: "Gibberellins (GAs), an important endogenous hormone, serve a crucial regulatory role in plants’ resistance to environmental stress, whereas it is unclear whether and how arbuscular mycorrhizal fungi (AMF) regulate the profile of GAs in plants exposed to soil water deficit (SWD). This study aimed to analyze how Rhizoglomus intraradices inoculation affected plant growth performance, antioxidant enzyme activities, and the composition, synthesis, metabolism, and signaling pathways of GAs in the roots of trifoliate orange (Poncirus trifoliata) under a 10-week SWD. Although SWD decreased both root AMF colonization and soil hyphal length, mycorrhizal plants nevertheless outperformed non-mycorrhizal plants in terms of growth performance, as well as peroxidase (70.0%) and catalase (149.2%) activities, indicating greater drought tolerance. A total of nine GAs compositions were detected in the roots, with bioactive GA4 exclusively found in AMF roots. AMF colonization significantly reduced bioactive GA3 levels by 37.9%, while it increased inactive GA8, GA9, and GA15 levels under SWD by 522.2%, 100.0%, and 2500.0%. Inoculation with AMF also up-regulated the expression of PtCPS, PtPKS, and PtKO in GA synthesis pathways of roots and the expression of PtGA20ox, PtGA3ox, and PtGA2ox in GA metabolisms under SWD. In addition, the expression of DELLA genes PtGaipb and PtGai associated with GA signaling pathways was further up-regulated under SWD by AMF inoculation. It is concluded that AMF regulated the composition, synthesis, and deactivation of GAs in roots to promote plant growth, along with an increase in PtGaipb and PtGai expression to possibly initiate mycorrhizal signaling pathways in response to SWD."
Authors: Zizhao Xie, Liang Jin, Ying Sun, Chenghang Zhan, Siqi Tang, Tian Qin, Nian Liu and Junli Huang.
Plant Communications (2024)
Abstract: "The crosstalk between gibberellin (GA) and abscisic acid (ABA) signaling is crucial for balancing plant growth and adaption to environmental stress. Nevertheless, the molecular mechanism of mutual antagonism still needs to be well understood. In this study, we find that knockout of rice NAC (NAM, ATAF1/2, CUC2) transcription factor gene OsNAC120 inhibits plant growth while enhances drought tolerance, but its overexpression lines act in an opposite way. Exogenous GA can rescue the semi-dwarf phenotype of osnac120 mutants, and further study shows that OsNAC120 promotes GA biosynthesis through transcriptionally activating GA biosynthetic genes OsGA20ox1 and OsGA20ox3. DELLA protein SLENDER RICE1 (SLR1) interacts with OsNAC120 and impedes its transactivation ability, while GA treatment can remove the inhibition of transactivation activity caused by SLR1. On the other hand, OsNAC120 negatively regulates rice drought tolerance by repressing ABA-induced stomatal closure. Mechanistic investigation illustrates that OsNAC120 inhibits ABA biosynthesis via transcriptional repression of ABA biosynthetic genes OsNCED3 and OsNCED4. Rice OSMOTIC STRESS/ABA-ACTIVATED PROTEIN KINASE 9 (OsSAPK9) physically interacts with OsNAC120 and mediates its phosphorylation, which results in OsNAC120 degradation. ABA treatment accelerates OsNAC120 degradation and reduces its transactivation activity. Together, our findings provide the evidence that OsNAC120 plays critical roles in balancing GA-mediated growth and ABA-induced drought tolerance in rice. The research will help us understand the mechanisms underlying the “trade-off” between plant growth and stress tolerance, and engineer stress-resistant and high-yielding crops."
Authors: Zhigang Liao, Yunchao Zhang, Qing Yu, Weicong Fang, Meiyao Chen, Tianfei Li, Yi Liu, Zaochang Liu, Liang Chen, Shunwu Yu, Hui Xia, Hong-Wei Xue, Hong Yu and Lijun Luo.
New Phytologist (2023)
Abstract: "The drought caused by global warming seriously affects the crop growth and agricultural production. Plants have evolved distinct strategies to cope with the drought environment. Under drought stress, energy and resources should be diverted from growth toward stress management. However, the molecular mechanism underlying coordination of growth and drought response remains largely elusive. Here, we discovered that most of the gibberellin (GA) metabolic genes were regulated by water scarcity in rice, leading to the lower GA contents and hence inhibited plant growth. Low GA contents resulted in the accumulation of more GA signaling negative regulator SLENDER RICE 1, which inhibited the degradation of abscisic acid (ABA) receptor PYL10 by competitively binding to the co-activator of anaphase-promoting complex TAD1, resulting in the enhanced ABA response and drought tolerance. These results elucidate the synergistic regulation of crop growth inhibition and promotion of drought tolerance and survival, and provide useful genetic resource in breeding improvement of crop drought resistance."
Authors: Hao Wu, Beibei Bai, Xiaoduo Lu and Haiyan Li.
Plant Cell Reports (2023)
Key message: The reduction in endogenous gibberellin improved drought resistance, but decreased cellulose and lignin contents, which made the mutant prone to lodging.
Abstract; "It is well known that gibberellin (GA) is a hormone that plays a vital role in plant growth and development. In recent years, a growing number of studies have found that gibberellin plays an important role in regulating the plant height, stem length, and stressed growth surfaces. In this study, a dwarf maize mutant was screened from an EMS-induced mutant library of maize B73. The mutated gene was identified as KS, which encodes an ent-kaurene synthase (KS) enzyme functioning in the early biosynthesis of GA. The mutant was named as ks3-1. A significant decrease in endogenous GA levels was verified in ks3-1. A significantly decreased stem strength of ks3-1, compared with that of wild-type B73, was found. Significant decreases in the cellulose and lignin contents, as well as the number of epidermal cell layers, were further characterized in ks3-1. The expression levels of genes responsible for cellulose and lignin biosynthesis were induced by exogenous GA treatment. Under drought stress conditions, the survival rate of ks3-1 was significantly higher than that of the wild-type B73. The survival rates of both wild-type B73 and ks3-1 decreased significantly after exogenous GA treatment. In conclusion, we summarized that a decreased level of GA in ks3-1 caused a decreased plant height, a decreased stem strength as a result of cell wall defects, and an increased drought tolerance. Our results shed light on the importance of GA and GA-defective mutants in the genetic improvement of maize and breeding maize varieties."
Authors: Xuanjun Feng, Jing Xiong, Weixiao Zhang, Huarui Guan, Dan zheng, Hao Xiong, Li Jia, Yue Hu, Hanmei Zhou, Ying Wen, Xuemei Zhang, Fengkai Wu, Qingjun Wang, Jie Xu and Yanli Lu.
The Plant Journal (2022)
Abstract: "Lateral organ boundaries domain (LBD) proteins are plant-specific transcription factors. Class-I LBD members have been widely demonstrated to play pivotal roles in organ development; however, knowledge on class-II members remains limited. Here, we report that ZmLBD5, a class-II LBD member, is involved in the regulation of maize growth and drought response by affecting gibberellin (GA) and abscisic acid (ABA) synthesis. ZmLBD5 is mainly involved in regulation of the TPS-KS-GA2ox gene module, which comprises key enzymatic genes upstream of GA and ABA biosynthesis. The insufficiency of ABA increases stomatal density and aperture in overexpressed plants, and causes the drought sensitive phenotype by promoting water transpiration. The increase of GA1 promoted seedling growth in overexpressed plants. Accordingly, the CRISPR/Cas9 knockout lbd5 seedlings were dwarf but drought tolerant. Moreover, lbd5 has larger grain yield under drought stress and no penalty in well watered conditions than the wild type. On the whole, ZmLBD5 is a negative regulator in maize drought tolerance, and it is a potentially useful target for drought resistance breeding."
Authors: Klára Ptošková, Marek Szecówka, Pavel Jaworek, Danuše Tarkowská, Ivan Petřík, Iva Pavlović, Ondřej Novák, Stephen G. Thomas, Andrew L. Phillips and Peter Hedden.
BMC Plant Biology (2022)
Abstract: "Background - Bread wheat (Triticum aestivum) is a major source of nutrition globally, but yields can be seriously compromised by water limitation. Redistribution of growth between shoots and roots is a common response to drought, promoting plant survival, but reducing yield. Gibberellins (GAs) are necessary for shoot and root elongation, but roots maintain growth at lower GA concentrations compared with shoots, making GA a suitable hormone for mediating this growth redistribution. In this study, the effect of progressive drought on GA content was determined in the base of the 4th leaf and root tips of wheat seedlings, containing the growing regions, as well as in the remaining leaf and root tissues. In addition, the contents of other selected hormones known to be involved in stress responses were determined. Transcriptome analysis was performed on equivalent tissues and drought-associated differential expression was determined for hormone-related genes. Results - After 5 days of applying progressive drought to 10-day old seedlings, the length of leaf 4 was reduced by 31% compared with watered seedlings and this was associated with significant decreases in the concentrations of bioactive GA1 and GA4 in the leaf base, as well as of their catabolites and precursors. Root length was unaffected by drought, while GA concentrations were slightly, but significantly higher in the tips of droughted roots compared with watered plants. Transcripts for the GA-inactivating gene TaGA2ox4 were elevated in the droughted leaf, while those for several GA-biosynthesis genes were reduced by drought, but mainly in the non-growing region. In response to drought the concentrations of abscisic acid, cis-zeatin and its riboside increased in all tissues, indole-acetic acid was unchanged, while trans-zeatin and riboside, jasmonate and salicylic acid concentrations were reduced. Conclusions - Reduced leaf elongation and maintained root growth in wheat seedlings subjected to progressive drought were associated with attenuated and increased GA content, respectively, in the growing regions. Despite increased TaGA2ox4 expression, lower GA levels in the leaf base of droughted plants were due to reduced biosynthesis rather than increased catabolism. In contrast to GA, the other hormones analysed responded to drought similarly in the leaf and roots, indicating organ-specific differential regulation of GA metabolism in response to drought."
Authors: Klára Ptošková, Marek Szecówka, Pavel Jaworek, Danuše Tarkowská, Ivan Petřík, Iva Pavlović, Ondřej Novák, Stephen G. Thomas, Andrew L. Phillips and Peter Hedden.
Research Square (2022)
Abstract: "Background - Bread wheat (Triticum aestivum) is a major source of nutrition globally, but yields can be seriously compromised by water limitation. Redistribution of growth between shoots and roots is a common response to drought, promoting plant survival, but reducing yield. Gibberellins (GAs) are necessary for shoot and root elongation, but roots maintain growth at lower GA concentrations compared with shoots, making GA a suitable hormone for mediating this growth redistribution. In this study, the effect of progressive drought on GA content was determined in the base of the 4th leaf and root tips of wheat seedlings, containing the growing regions, as well as in the remaining leaf and root tissues. In addition, the contents of other selected hormones known to be involved in stress responses were determined. Transcriptome analysis was performed on equivalent tissues and drought-associated differential expression was determined for hormone-related genes. Results - After 5 days of applying progressive drought to 10-day old seedlings, the length of leaf 4 was reduced by 31% compared with watered seedlings and this was associated with significant decreases in the concentrations of bioactive GA1 and GA4 in the leaf base, as well as of their catabolites and precursors. Root length was unaffected by drought, while GA concentrations were slightly, but significantly higher in the tips of droughted roots compared with watered plants. Transcripts for the GA-inactivating gene TaGA2ox4 were elevated in the droughted leaf, while those for several GA-biosynthesis genes were reduced by drought, but mainly in the non-growing region. In response to drought the concentrations of abscisic acid, cis-zeatin and its riboside increased in all tissues, indole-acetic acid was unchanged, while trans-zeatin and riboside, jasmonate and salicylic acid concentrations were reduced. Conclusions - Reduced leaf elongation and maintained root growth in wheat seedlings subjected to progressive drought were associated with attenuated and increased GA content, respectively, in the growing regions. Despite increased TaGA2ox4 expression, lower GA levels in the leaf base of droughted plants were due to reduced biosynthesis rather than increased catabolism. In contrast to GA, the other hormones analysed responded to drought similarly in the leaf and roots, indicating organ-specific differential regulation of GA metabolism in response to drought."
Authors: Yaping Zhang, Ayla Norris, Michael S. Reid and Cai-Zhong Jiang.
Ornamental Plant Research (2021)
Abstract: "Improving plants' ability to survive under drought is of great importance to the horticultural industry. The plant hormone gibberellic acid (GA) mediates diverse aspects of plant growth and development. The Arabidopsis gibberellin acid insensitive mutant gai-1 displays reduced plant height, altered GA response, and enhanced drought resistance. However, overexpression of gai-1 using the constitutive 35S promoter would result in dwarf plants with drought resistance. Here, we tested the hypothesis that the temporary inhibition of cell growth caused by inducible expression of the gai-1 gene would lead to better drought resistance and improve crop productivity without an undesirable dwarf phenotype. We generated transgenic plants in which the gai-1 gene was over-expressed in petunia, under a stress-inducible RD29A promoter from Arabidopsis. When these plants were subjected to limited irrigation and drought treatments, transgenic plants showed phenotypes of darker green leaves and compact flowers compared to the wild type plants. Importantly, these transgenic plants recovered sooner than wild type and the empty vector-transformed control plants. This study provides evidence that temporary inhibition of cell growth caused by over-expression of the gai-1 mutant gene with a drought stress-inducible promoter leads to better drought resistance when the plants experience drought conditions".
Authors: Hagai Shohat, Hadar Cheriker, Himabindu Vasuki Kilambi, Natanella Illouz Eliaz, Shula Blum, Ziva Amsellem, Danuše Tarkowská, Asaph Aharoni, Yuval Eshed and David Weiss.
New Phytologist (2021)
Abstract: "Plants reduce transpiration to avoid dehydration during drought episodes by stomatal closure and inhibition of canopy growth. Previous studies suggest that low gibberellin (GA) activity promotes these 'drought avoidance' responses. Using genome editing, molecular, physiological and hormone analyses, we examined if drought regulates GA metabolism in tomato (Solanum lycopersicum) guard cells and leaves, and studied how this affects water loss. Water deficiency inhibited the expression of the GA biosynthesis genes GA20 oxidase1 (GA20ox1) and GA20ox2 and induced the GA-deactivating gene GA2ox7 in guard cells and leaf tissue, resulting in reduced levels of bioactive GAs. These effects were mediated by ABA-dependent and independent pathways, and by the transcription factor TINY1. The loss of GA2ox7 attenuated stomatal response to water deficiency and during soil dehydration, ga2ox7 plants closed their stomata later, and wilted faster than wild type (WT) M82 cv. Mutations in GA20ox1 and GA20ox2, had no effect on stomatal closure, but reduced water loss due to the mutants' smaller canopy area. The results suggest that drought-induced GA deactivation in guard cells, contributes to stomatal closure at the early stages of soil dehydration, whereas inhibition of GA synthesis in leaves, suppresses canopy growth and restrict transpiration area.
Authors: Hagai Shohat, Hadar Cheriker, Himabindu Vasuki, Natanella Illouz-Eliaz, Shula Blum, Ziva Amsellem, Danuše Tarkowská, Asaph Aharoni, Yuval Eshed and David Weiss.
bioRxiv (2021)
Abstract: "Plants reduce transpiration to avoid dehydration during drought episodes by stomatal closure and inhibition of canopy growth. While abscisic acid (ABA) has a primary role in ‘drought avoidance’, previous studies suggest that gibberellin (GA), might also be involved. Here we show in tomato (Solanum lycopersicum) that shortage of water inhibited the expression of the GA biosynthesis genes GA20 oxidase1 (GA20ox1) and GA20ox2 and induced the GA-deactivating gene GA2ox7 in leaves and guard cells, resulting in reduced bioactive GA levels. Drought regulation of GA metabolism was mediated by ABA-dependent and independent pathways, and by the transcription factor DEHYDRATION RESPONSIVE ELEMENT BINDING (DREB), TINY1. Mutations in GA20ox1 and GA20ox2 reduced water loss due to the smaller canopy area. On the other hand, loss of GA2ox7 did not affect leaf size, but attenuated stomatal response to water deficiency; during soil dehydration, ga2ox7 plants closed their stomata and reduced transpiration later than WT, suggesting that ga2ox7 stomata are hyposensitive to soil dehydration. Together, the results suggest that drought-induced GA deactivation in guard cells contributes to stomatal closure at the early stages of soil dehydration, whereas inhibition of GA synthesis in leaves promotes mainly the long-term reduction in canopy growth to reduce transpiration area."
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