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Authors: Enrico Scarpella
Plant Physiology (2023)
Abstract: "For multicellular organisms to develop, cells must grow, divide, and differentiate along preferential or exclusive orientations or directions. Moreover, those orientations—or axes—and directions—or polarities—must be coordinated between cells within and between tissues. Therefore, how axes and polarities are coordinated between cells is a key question in biology. In animals, such coordination mainly depends on cell migration and direct interaction between proteins protruding from the plasma membrane. Both cell movements and direct cell–cell interactions are prevented in plants by cell walls that surround plant cells and keep them apart and in place. Therefore, plants have evolved unique mechanisms to coordinate their cell axes and polarities. Here I will discuss evidence suggesting that understanding how leaf veins form may uncover those unique mechanisms. Indeed—unlike previously thought—the cell-to-cell, polar transport of the plant hormone auxin along developing veins cannot account for many features of vein patterning. Instead, those features can be accounted for by models of vein patterning that combine polar auxin transport with auxin diffusion through plasmodesmata along the axis of developing veins. Though it remains unclear whether such a combination of polar transport and axial diffusion of auxin can account for the formation of the variety of vein patterns found in plant leaves, evidence suggests that such a combined mechanism may control plant developmental processes beyond vein patterning."
Authors: Jianhua Yue, Di Zhang, Guanqun Chen and Xiaohui Shen.
Scientia Horticulturae (2023)
Highlights • The main bioactive gibberellin controlling scape height in Agapanthus praecox is GA4. • ApGA20ox1 controls the biosynthesis of GA4 in Agapanthus praecox. • Suppression of ApGA20ox1 resulted in poor somatic embryogenesis potential in Agapanthus praecox. • ApGA20ox1 contributed to leaf elongation and plant height by affecting longitudinal cell length in Agapanthus praecox. • Suppression of ApGA20ox1 resulted in poor stress resistance traits in plant development of Agapanthus praecox.
Abstract: "Agapanthus praecox is cultivated worldwide as an ornamental plant, and a dwarf ideotype has become more popular due to its superior lodging resistance and its suitability for use in cut flowers. The main bioactive gibberellin (GA) controlling scape height in A. praecox is GA4. A GA biosynthesis gene, ApGA20ox1, controls GA4 biosynthesis in this species. Here, we report the development of an A. praecox dwarf phenotype, which was generated by targeted suppression of the biosynthetic pathway for GAs. We utilized Agrobacterium-mediated genetic transformation using embryogenic callus with RNA interference (RNAi) to selectively reduce the expression of the ApGA20ox1 gene. Interestingly, suppression of ApGA20ox1 resulted in poor somatic embryogenesis potential in A. praecox, which was accompanied by a higher accumulation of hydrogen peroxide and poorer catalase activity. Subsequently, the RNAi plantlets showed lower GA levels, leading to inhibition of cell longitudinal size in leaves, which reduced plant height. Furthermore, the dwarf (RNAi) plantlets accumulated higher levels of saccharides and plant hormones such as indole acetic acid (IAA) and abscisic acid (ABA) than the wild type accumulated. However, the levels of endogenous hormones such as GAs, brassinosteroids (BRs), cytokinins (CTKs), which respond to cell proliferation and cell expansion, were significantly decreased. Isobaric tags for relative and absolute quantification (iTRAQ) proteomics revealed that differentially accumulated proteins (DAPs) were enriched differently between control and RNAi plantlets in the categories of cell wall, hormone metabolism, carbohydrate metabolism and stress response. This study provides new insights into the role of GAs in the process of somatic embryogenesis and plant height control in A. praecox."
Author: Jorge J. Casal.
Current Biology (2023)
Excerpts: "Summary - When neighbouring competitors shade the tip of a leaf, differential growth at the other end of the organ elevates its position to avoid shade. A new study elucidates how waves of growth hormones communicate these distant leaf sectors."
"To maximise the interception of sunlight coming from the zenith, plants isolated from neighbours orient the surface of their leaves horizontally. Since, in horizontal leaves, the tip is closer than the base to the surrounding vegetation, the tip is the most likely sector to receive shade when neighbours encroach on the plant’s sunlight. Therefore, the tip of the leaf is optimal for competitive surveillance. As illustrated in Figure 1, the photo-sensory receptor phytochrome B perceives the early warning generated by neighbour cues reaching the tip of the leaf, which rapidly abandons its horizontal position to become more erect1,2 and elude the shaded area. This response, called hyponasty, involves faster growth of the abaxial compared with the adaxial face of the base of the leaf (the petiole) attached to the rest of the plant. In this issue of Current Biology, Küpers et al.3 unravel the mechanisms by which distal perception of the threat results in differential growth at the base of the leaf."
"Another intriguing observation by Küpers et al.3 was the enhanced expression of genes related to the growth hormone gibberellin, which occurred concomitantly with the auxin gene response in the abaxial half of the petiole (Figure 1)."
Authors: Qingqing Wang, Marco Marconi, Chunmei Guan, Krzysztof Wabnik and Yuling Jiao.
PNAS (2022)
Significance: "Flattened leaf blade formation is a key adaption of plants to the environment, but its developmental regulation remains to be resolved. Classical microsurgery experiments suggest that a mobile signal, known as the Sussex signal, in the shoot apex is required for flattened leaf formation. A recent study found that polar auxin transport contributes to the Sussex signal, but how microsurgeries interact with polarity genes remains elusive. Here, we combine live-imaging and computer model simulations to show that an oval-shaped auxin response in inner cells of leaf primordium is essential for the formation of bipolar SlLAM1 expression domain, which establishes initial bilateral leaf primordia. Microsurgeries lead to an axisymmetric domain shape and can interfere with other polarity factors.
Abstract: "The flattened leaf form is an important adaptation for efficient photosynthesis, and the developmental process of flattened leaves has been intensively studied. Classic microsurgery studies in potato and tomato suggest that the shoot apical meristem (SAM) communicates with the leaf primordia to promote leaf blade formation. More recently, it was found that polar auxin transport (PAT) could mediate this communication. However, it is unclear how the expression of leaf patterning genes is tailored by PAT routes originating from SAM. By combining experimental observations and computer model simulations, we show that microsurgical incisions and local inhibition of PAT in tomato interfere with auxin transport toward the leaf margins, reducing auxin response levels and altering the leaf blade shape. Importantly, oval auxin responses result in the bipolar expression of SlLAM1 that determines leaf blade formation. Furthermore, wounding caused by incisions promotes degradation of SlREV, a known regulator of leaf polarity. Additionally, computer simulations suggest that local auxin biosynthesis in early leaf primordia could remove necessity for external auxin supply originating from SAM, potentially explaining differences between species. Together, our findings establish how PAT near emerging leaf primordia determines spatial auxin patterning and refines SlLAM1 expression in the leaf margins to guide leaf flattening."
Authors: Ziyuan Peng, Daniel Alique, Yuanyuan Xiong, Jinrong Hu, Xiuwei Cao, Shouqin Lü, Mian Long, Ying Wang, Krzysztof Wabnik and Yuling Jiao.
Current Biology (2022)
Editor's view: Peng et al. show that different growth dynamics determine the shape of plant aerial organs, leaf and floral primordia, which share similar initial geometry. Experiments and simulations are combined to link growth dynamics with biomechanics and polar auxin transport.
Highlights: • Leaf and floral primordia share similar gene expression and initial domain partition • Local growth-rate differences across domains explain primordia shape differences • Two primordia have different patterns of cell-wall rigidity and auxin convergence • When incorporating growth dynamics, models explain different organ shapes
Abstract: "How gene activities and biomechanics together direct organ shapes is poorly understood. Plant leaf and floral organs develop from highly similar initial structures and share similar gene expression patterns, yet they gain drastically different shapes later—flat and bilateral leaf primordia and radially symmetric floral primordia, respectively. We analyzed cellular growth patterns and gene expression in young leaves and flowers of Arabidopsis thaliana and found significant differences in cell growth rates, which correlate with convergence sites of phytohormone auxin that require polar auxin transport. In leaf primordia, the PRESSED-FLOWER-expressing middle domain grows faster than adjacent adaxial domain and coincides with auxin convergence. In contrast, in floral primordia, the LEAFY-expressing domain shows accelerated growth rates and pronounced auxin convergence. This distinct cell growth dynamics between leaf and flower requires changes in levels of cell-wall pectin de-methyl-esterification and mechanical properties of the cell wall. Data-driven computer model simulations at organ and cellular levels demonstrate that growth differences are central to obtaining distinct organ shape, corroborating in planta observations. Together, our study provides a mechanistic basis for the establishment of early aerial organ symmetries through local modulation of differential growth patterns with auxin and biomechanics."
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: 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: Quanzi Bai, Wenjing Yang, Guochen Qin, Baolin Zhao, Liangliang He, Xuan Zhang, Weiyue Zhao, Dian Zhou, Ye Liu, Yu Liu, Hua He, Million Tadege, Yan Xiong, Changning Liu and Jianghua Chen.
International Journal of Molecular Sciences (2022)
Abstract: "Nyctinastic leaf movement of Fabaceae is driven by the tiny motor organ pulvinus located at the base of the leaf or leaflet. Despite the increased understanding of the essential role of ELONGATED PETIOLULE1 (ELP1)/PETIOLE LIKE PULVINUS (PLP) orthologs in determining pulvinus identity in legumes, key regulatory components and molecular mechanisms underlying this movement remain largely unclear. Here, we used WT pulvinus and the equivalent tissue in the elp1 mutant to carry out transcriptome and proteome experiments. The omics data indicated that there are multiple cell biological processes altered at the gene expression and protein abundance level during the pulvinus development. In addition, comparative analysis of different leaf tissues provided clues to illuminate the possible common primordium between pulvinus and petiole, as well as the function of ELP1. Furthermore, the auxin pathway, cell wall composition and chloroplast distribution were altered in elp1 mutants, verifying their important roles in pulvinus development. This study provides a comprehensive insight into the motor organ of the model legume Medicago truncatula and further supplies a rich dataset to facilitate the identification of novel players involved in nyctinastic movement."
Authors: Yajing Song, Ruofan Niu, Hongli Yu, Jing Guo, Chunhui Du, Zilun Zhang, Ying Wei, Jiaxue Li, Suqiao Zhang.
The Plant Journal (2022)
Abstract: "Leaf angle is an important trait in plants. Here, we demonstrate that the leucine-rich-repeat receptor-like kinase (LRR-RLK) OsSLA1 plays an important role in leaf angle regulation. OsSLA1 mutant plants exhibited a small leaf angle phenotype due to changes of adaxial cells in the lamina joint. GUS staining revealed that OsSLA1 was highly expressed in adaxial cells of the lamina joint. The OsSLA1 mutant plants were insensitive to exogenous eBL and showed up-regulated expression of DWARF and CPD, but down-regulated expression of BU1, BUL1, and ILI1, indicating that BR signal transduction was blocked. Fluorescence microscopy showed that OsSLA1 was localized to the plasma membrane and nearby periplasmic vesicles. Further study showed that OsSLA1 interacts with OsBRI1 and OsBAK1 via its intracellular domain and promotes the interaction between OsBRI1 and OsBAK1. In addition, phosphorylation experiments revealed that OsSLA1 does not possess kinase activity, but that it can be phosphorylated by OsBRI1 in vitro. The knockout of OsSLA1 in the context of d61 caused exacerbation of the mutant phenotype. These results demonstrate that OsSLA1 regulates leaf angle formation via positive regulation of BR signaling by enhancing the interaction of OsBRI1 with OsBAK1."
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Authors: Huihui Wan, Lei Ren, Jianfeng Ma, Ya Li, Hairong Xu, Huijuan Yao, Yuting Dai, Liwei Wang, Shengyue Li, Zongyun Li, Daifu Ma and Aimin Wang.
Scientia Horticulturae (2023)
Highlights • Seven IbGA2ox genes were identified and cloned in the hexaploid sweet potato. • IbGA2ox genes exhibited distinctive tissue-specific and dynamic GA3 response expression patterns. • Seven IbGA2ox proteins were confirmed locating in nucleus and cytoplasm by transient expression assay. • Ectopic overexpression of the IbGA2ox genes in tobacco results in dwarf traits which can be restored by exogenous GA3.
Abstract: "Gibberellins (GAs), important endogenous plant hormones, play multiple roles in plant growth regulation. GA2-oxidases (GA2oxs), a gibberellin-deactivating enzyme, catalyze active GAs into inactive GAs thus regulating the level of active GAs in plants. However, there is little information available on GA2oxs in sweet potato. In this study, seven IbGA2ox genes in sweet potato were identified. The domain structures, phylogeny, and expression patterns were investigated. A subcellular location assay showed that IbGA2oxs were located in the nucleus and cytoplasm. Overexpressing these genes in tobacco resulted in dwarf traits with smaller leaves, shorter and slimmer stems, and later flowering compared with the wild type. These results suggest that IbGA2oxs mainly affect plant stature and flowering time. Our findings provide candidate genes for the molecular breeding of sweet potato."
Authors: Yanjun Zhang, Shaqila Han, Yuqing Lin, Jiyue Qiao, Naren Han, Yanyan Li, Yaning Feng, Dongming Li and Yanhua Qi.
Plants (2023)
Abstract: "Leaf inclination is one of the most important components of the ideal architecture, which effects yield gain. Leaf inclination was shown that is mainly regulated by brassinosteroid (BR) and auxin signaling. Here, we reveal a novel regulator of leaf inclination, auxin transporter OsPIN1b. Two CRISPR-Cas9 homozygous mutants, ospin1b-1 and ospin1b-2, with smaller leaf inclination compared to the wild-type, Nipponbare (WT/NIP), while overexpression lines, OE-OsPIN1b-1 and OE-OsPIN1b-2 have opposite phenotype. Further cell biological observation showed that in the adaxial region, OE-OsPIN1b-1 has significant bulge compared to WT/NIP and ospin1b-1, indicating that the increase in the adaxial cell division results in the enlarging of the leaf inclination in OE-OsPIN1b-1. The OsPIN1b was localized on the plasma membrane, and the free IAA contents in the lamina joint of ospin1b mutants were significantly increased while they were decreased in OE-OsPIN1b lines, suggesting that OsPIN1b might action an auxin transporter such as AtPIN1 to alter IAA content and leaf inclination. Furthermore, the OsPIN1b expression was induced by exogenous epibrassinolide (24-eBL) and IAA, and ospin1b mutants are insensitive to BR or IAA treatment, indicating that the effecting leaf inclination is regulated by OsPIN1b. This study contributes a new gene resource for molecular design breeding of rice architecture."
Authors: Jesse J. Küpers, Basten L. Snoek, Lisa Oskam, Chrysoula K. Pantazopoulou, Sanne E. A. Matton, Emilie Reinen, Che-Yang Liao, Eline D. C. Eggermont, Harold Weekamp, Muthanna Biddanda-Devaiah, Wouter Kohlen, Dolf Weijers and Ronald Pierik.
Current Biology (2023)
Highlights: • Temporal transcriptome patterns in response to shade cues in leaf segments • Tissue-specific quantification of auxin reporter in petioles • Auxin and Gibberellin interactively regulate leaf movement • Mechanisms underpinning physical separation of light signaling and response
Abstract: "Although plants are immobile, many of their organs are flexible to move in response to environmental cues. In dense vegetation, plants detect neighbors through far-red light perception with their leaf tip. They respond remotely, with asymmetrical growth between the abaxial and adaxial sides of the leafstalk, the petiole. This results in upward movement that brings the leaf blades into better lit zones of the canopy. The plant hormone auxin is required for this response, but it is not understood how non-differential leaf tip-derived auxin can remotely regulate movement. Here, we show that remote signaling of far-red light promotes auxin accumulation in the abaxial petiole. This local auxin accumulation is facilitated by reinforcing an intrinsic directionality of the auxin transport protein PIN3 on the petiole endodermis, as visualized with a PIN3-GFP line. Using an auxin biosensor, we show that auxin accumulates in all cell layers from endodermis to epidermis in the abaxial petiole, upon far-red light signaling in the remote leaf tip. In the petiole, auxin elicits a response to both auxin itself as well as a second growth promoter; gibberellin. We show that this dual regulation is necessary for hyponastic leaf movement in response to light. Our data indicate that gibberellin is required to permit cell growth, whereas differential auxin accumulation determines which cells can grow. Our results reveal how plants can spatially relay information about neighbor proximity from their sensory leaf tips to the petiole base, thus driving adaptive growth."
Authors: Batist Geldhof, Jolien Pattyn, Petar Mohorović, Karlien Van den Broeck, Vicky Everaerts, Ondřej Novák and Bram Van de Poel.
bioRxiv (2022)
Abstract: "Developing leaves undergo a vast array of age-related changes as they mature. These include physiological, hormonal and morphological changes that determine their adaptation plasticity towards adverse conditions. Waterlogging induces leaf epinasty in tomato, and the magnitude of leaf bending is intricately related to the age-dependent cellular and hormonal response. We now show that ethylene, the master regulator of epinasty, is differentially regulated throughout leaf development, giving rise to age-dependent epinastic responses. Young leaves have a higher basal ethylene production, but are less responsive to waterlogging-induced epinasty, as they have a higher capacity to convert the root-borne and mobilized ACC into the inactive conjugate MACC. Ethylene stimulates cell elongation relatively more at the adaxial petiole side, by activating auxin biosynthesis and locally inhibiting its transport through PIN4 and PIN9 in older and mature leaves. As a result, auxins accumulate in the petiole base of these leaves and enforce partially irreversible epinastic bending upon waterlogging. Young leaves maintain their potential to transport auxins, both locally and through the vascular tissue, leading to enhanced flexibility to dampen the epinastic response and a faster upwards repositioning during reoxygenation. This mechanism also explains the observed reduction of epinasty during and its recovery after waterlogging in the anthocyanin reduced (are) and Never ripe (Nr) mutants, both characterized by higher auxin flow. Our work has demonstrated that waterlogging activates intricate hormonal crosstalk between ethylene and auxin, controlled in an age-dependent way."
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: Hui Wang, Xue Li, Tezera Wolabu, Ziyao Wang, Ye Liu, Dimiru Tadesse, Naichong Chen, Aijiao Xu, Xiaojing Bi, Yunwei Zhang, Jianghua Chen and Million Tadege.
The Plant Cell (2022)
Abstract: "The plant-specific family of WUSCHEL (WUS)-related homeobox (WOX) transcription factors is key regulators of embryogenesis, meristem maintenance, and lateral organ development in flowering plants. The modern/WUS clade transcriptional repressor STENOFOLIA/LAMINA1(LAM1), and the intermediate/WOX9 clade transcriptional activator MtWOX9/NsWOX9 antagonistically regulate leaf blade expansion, but the molecular mechanism is unknown. Using transcriptome profiling and biochemical methods, we determined that NsCKX3 is the common target of LAM1 and NsWOX9 in Nicotiana sylvestris. LAM1 and NsWOX9 directly recognize and bind to the same cis-elements in the NsCKX3 promoter to repress and activate its expression, respectively, thus controlling the levels of active cytokinins in vivo. Disruption of NsCKX3 in the lam1 background yielded a phenotype similar to the knockdown of NsWOX9 in lam1, while overexpressing NsCKX3 resulted in narrower and shorter lam1 leaf blades reminiscent of NsWOX9 overexpression in the lam1 mutant. Moreover, we established that LAM1 physically interacts with NsWOX9, and this interaction is required to regulate NsCKX3 transcription. Taken together, our results indicate that repressor and activator WOX members oppositely regulate a common downstream target to function in leaf blade outgrowth, offering a novel insight into the role of local cytokinins in balancing cell proliferation and differentiation during lateral organ development."
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: Jesse J. Küpers, Basten L. Snoek, Lisa Oskam, Chrysoula K. Pantazopoulou, Sanne E. A. Matton, Emilie Reinen, Che-Yang Liao, Eline D.C. Eggermont, Harold Weekamp, Wouter Kohlen, Dolf Weijers and Ronald Pierik.
bioRxiv (2022)
Abstract: "Although plants are immobile, many of their organs are flexible to move in response to environmental cues. In dense vegetation plants detect neighbours through far-red light perception with their leaf tip. They respond remotely, with asymmetrical growth between the abaxial and adaxial sides of the leafstalk, the petiole. This results in upward movement that brings the leaf blades into better lit zones of the canopy. The plant hormone auxin is required for this response, but it is not understood how non-differential leaf tip-derived auxin can remotely regulate movement. Here we show that remote light signalling promotes auxin accumulation in the abaxial petiole by reinforcing an intrinsic auxin transport directionality. In the petiole, auxin elicits a response of both auxin as well as a second growth promoter; gibberellin. We show that this dual regulation is necessary for hyponastic leaf movement in response to light. Our results reveal how plants can spatially relay information about neighbour proximity from their sensory leaf tips to the petiole base, thus driving adaptive growth."
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