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Author: Gwendolyn K. Kirschner.
The Plant Cell (2024)
Excerpts: "Yuxiang Li, Juan Wang and colleagues (Li et al. 2024) now connect the two roles of ethylene: as a signal responding to soil compaction and to trigger crown root development. In this work, they mimicked different levels of compaction by increasing agar concentrations and compared the growth of wildtype plants and ethylene signaling mutants. They found that compaction triggered crown root initiation via an ethylene-dependent pathway (Figure, A), and manipulating ethylene-related regulators influenced both root development and grain yield, implying that these regulators balance both root and grain development."
"By analyzing crown root numbers and transcript levels in oswox11 and ethylene signaling mutants, or overexpression combinations under normal or compacted soil conditions, the authors confirmed that the ethylene-OsEIL1-OsWOX11 module facilitates crown root development in compacted soil (Figure, B)."
Authors: Sompop Pinit, Lalichat Ariyakulkiat and Juthamas Chaiwanon.
Scientific Reports (2023)
Abstract: "Plant-derived smoke has been shown to promote plant growth and seed germination, but its roles and mechanisms in response to nutrient deficiency stress remain unclear. Plants respond to phosphorus (P) deficiency by undergoing morphological, physiological, and transcriptional changes in order to improve nutrient uptake efficiency. Here, we showed that rice straw-derived smoke water could promote root growth in rice (Oryza sativa cv. Nipponbare) grown under P-sufficient and P-deficient conditions. Transcriptome analysis of the root tissues identified 1309 genes up-regulated and 1311 genes down-regulated by smoke water under P-deficient conditions. The GO terms ‘glutathione transferase activity’ and ‘photosynthesis—light reaction’ were found to be significantly enriched among the genes that were up- and down-regulated by smoke water, respectively. Biochemical analysis showed that smoke water reduced P-deficient-induced accumulation of H2O2 and malondialdehyde (MDA), a lipid peroxidation marker, reduced sucrose contents, but increased Fe accumulation. Furthermore, smoke water suppressed the expression of strigolactone biosynthesis genes, which were strongly induced by P deficiency as an adaptive strategy to improve root P uptake. These results revealed a potential mechanism by which smoke water promotes root growth and interacts with P deficiency-induced transcriptional regulation to mitigate P deficiency stress in rice."
Authors: Qingwen Wang, Tao Shen, Lan Ni, Chao Chen, Jingjing Jiang, Zhenzhen Cui, Shuang Wang, Fengjuan Xu, Runjiao Yan and Mingyi Jiang.
Molecular Plant (2023)
Abstract: "In rice, the Ca2+/calmodulin-dependent protein kinase OsDMI3 is an important positive regulator of abscisic acid (ABA) signaling. In ABA signaling, H2O2 is required for ABA-induced activation of OsDMI3, which in turn increase H2O2 production. However, how OsDMI3 regulates H2O2 production in ABA signaling remains unknown. Here we show that OsRbohB is the main NADPH oxidase involved in ABA-induced H2O2 production and ABA-mediated physiological responses. OsDMI3 directly interacts with and phosphorylates OsRbohB at Ser-191, which is OsDMI3-mediated site-specific phosphorylation in ABA signaling. Further analyses revealed that OsDMI3-mediated OsRbohB Ser-191 phosphorylation positively regulates the activity of NADPH oxidase and the production of H2O2 in ABA signaling, thereby enhancing the sensitivity of seed germination and root growth to ABA and plant tolerance to water stress and oxidative stress. Moreover, we discovered that the OsDMI3-mediated OsRbohB phosphorylation and H2O2 production is dependent on the sucrose non-fermenting 1-related protein kinases SAPK8/9/10, which phosphorylate OsRbohB at Ser-140 in ABA signaling. Taken together, these results not only reveal an important regulatory mechanism that directly activates Rboh for ABA-induced H2O2 production but also uncover the importance of this regulatory mechanism in ABA signaling."
Authors: Runming Zhang, Yanlong Dong, Yuanyuan Li, Guangyue Ren, Chao Chen and Xiaoxia Jin.
Gene (2023)
Highlights: • The over-expression of SLs signaling pathway gene CsMAX2 increased the tolerance to salt, drought and ABA stress of Arabidopsis thaliana L. • CsMAX2 might improve plant tolerance by regulating the expression of stress related genes, ABA signaling pathway and SLs related genes. • The stress tolerance induced by CsMAX2 might be related to ABA, and it preliminary concluded that there was partially correlation between SLs and ABA.
Abstract: "Recent studies have demonstrated that strigolactones (SLs) participate in the regulation of stress adaptation, however, the mechanisms remain elusive. MAX2 (MORE AXILLARY GROWTH2) is the key gene in the signal transduction pathway of SLs. This study aimed to clone and functionally characterize the CsMAX2 gene of cucumber in Arabidopsis. The results showed that the expression levels of the CsMAX2 gene changed significantly after salt, drought, and ABA stresses in cucumber. Moreover, the overexpression of CsMAX2 promoted stress tolerance and increased the germination rate and root length of Arabidopsis thaliana. Meanwhile, the content of chlorophyll increased and malondialdehyde decreased in CsMAX2 OE lines under salt and drought stresses. Additionally, the expression levels of stress-related marker genes, especially AREB1 and COR15A, were significantly upregulated under salt stress, while the expression levels of all genes were upregulated under drought stress, except ABI4 and ABI5 genes. The level of NCED3 continued to rise under both salt and drought stresses. In addition, D10 and D27 gene expression level also showed a continuous increase under ABA stress. The result suggested the interaction between SL and ABA in the process of adapting to stress. Overall, CsMAX2 could positively regulate salt, drought, and ABA stress resistance, and this process correlated with ABA transduction."
Authors: Chun-Lin Shi and Liuji Wu.
Molecular Plant (2022)
Excerpts: "How these peptides interact with their receptors to play signaling roles in plants are not well defined. Recently, a study by Ogawa-Ohnishi et al. (2022) has successfully identified three LRR-RKs (PSYR1-3) for PSY5, PSY6 and PSY8, and demonstrated that the PSY-PSYR signaling pathway plays an important role in mediating the trade-off between plant growth and plant stress response in Arabidopsis."
"Although the exogenous application of synthetic PSY5 promoted root growth in seedlings, the psy5psy6psy8 triple mutant had no effect on root growth, suggesting functional redundancy of the PSYs. Consistently, the tyrosine-sulfated peptides deficient mutant, tpst, displayed significantly short root; and this phenotype was partially rescued by exogenous application of synthetic PSY5. Surprisingly, the psyr1psyr2psyr3 triple mutant showed slightly increased root length, indicating that PSYs may act as inhibitors of PSYR."
"Similar mutant phenotype between peptide ligands and their receptors has been generally used as a genetic approach matching the ligand-receptor pairs. In contrast, the PSY-PSYR ligandreceptor pair displays a novel mechanism of peptide signaling (Figure 1)."
Authors: Naoki Takahashi, Soichi Inagaki, Kohei Nishimura, Hitoshi Sakakibara, Ioanna Antoniadi, Michal Karady, Karin Ljung andMasaaki Umeda.
Science Advances (2021)
One-sentence summary: Plant hormones cytokinin and auxin orchestrate differential DNA damage responses in Arabidopsis roots.
Abstract: "Plants have a high ability to cope with changing environments and grow continuously throughout life. However, the mechanisms by which plants strike a balance between stress response and organ growth remain elusive. Here, we found that DNA double-strand breaks enhance the accumulation of cytokinin hormones through the DNA damage signaling pathway in the Arabidopsis root tip. Our data showed that activation of cytokinin signaling suppresses the expression of some of the PIN-FORMED genes that encode efflux carriers of another hormone, auxin, thereby decreasing the auxin signals in the root tip and causing cell cycle arrest at G2 phase and stem cell death. Elevated cytokinin signaling also promotes an early transition from cell division to endoreplication in the basal part of the root apex. We propose that plant hormones spatially coordinate differential DNA damage responses, thereby maintaining genome integrity and minimizing cell death to ensure continuous root growth."
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Authors: Tanya Singh, Nikita Bisht, Mohd Mogees Ansari and Puneet Singh Chauhan.
Plant Physiology and Biochemistry (2024)
Highlights • Plant roots play an essential role in adapting to environmental cues. • Coordinated cellular processes are driven by ROS and plant hormones. • Bidirectional interaction of ROS and hormones shapes plant root development. • ROS-hormone interplay offers agricultural potential to enhance plant stress resilience.
Abstract: "Root system architecture, encompassing lateral roots and root hairs, plays a vital in overall plant growth and stress tolerance. Reactive oxygen species (ROS) and plant hormones intricately regulate root growth and development, serving as signaling molecules that govern processes such as cell proliferation and differentiation. Manipulating the interplay between ROS and hormones has the potential to enhance nutrient absorption, stress tolerance, and agricultural productivity. In this review, we delve into how studying these processes provides insights into how plants respond to environmental changes and optimize growth patterns to better control cellular processes and stress responses in crops. We discuss various factors and complex signaling networks that may exist among ROS and phytohormones during root development. Additionally, the review highlights possible role of reactive nitrogen species (RNS) in ROS-phytohormone interactions and in shaping root system architecture according to environmental cues."
Authors: Miguel-Ángel Torres and Diego José Berlanga.
Molecular Plant (2023)
Excerpt: "In the accompanying article, Wang et al. (2023) identify in rice a new kinase that activates RBOH-dependent ROS production in ABA signaling. Rice Ca2+/CALMODULIN-DEPENDENT PROTEIN KINASE (CCaMK) DOESN'T MAKE INFECTIONS 3 (DMI3) was previously recognized as a positive regulator of ABA signaling, increasing ABA sensitivity and stress tolerance, and promoting the induction of antioxidant defences (Ni et al., 2019). In the present study, Wang et al. (2023) identify OsRBOHB as the main NADPH oxidase involved in ABA induced H2O2 production, and show that OsDMI3 interacts with and phosphorylates OsRBOHB at Ser-191. This phosphorylation positively regulates and enhances the production of H2O2 in ABA signaling, thereby increasing the sensitivity of seed germination and root growth to ABA and the tolerance of rice plants to drought and oxidative stress. The discovery of this novel regulatory mechanism of RBOH-dependent ROS production linked to Ca2+ signaling, added to the recent identification of proteins functioning as H2O2 sensors, point to the existence of positive feed-back regulatory loops to amplify H2O2 signaling and enhance downstream responses (Figure 1)."
Text of Figure: "Several amplification loops enhance H2O2 production and Ca2+ signaling in response to ABA. In the presence of ABA, loss of inhibition by class A PP2Cs activates SnRK2s (like OsSAPK8/9/10) that phosphorylate different targets, including RBOHs (Ser-140 in OsRBOHB) to trigger initial apoplastic H2O2 production. Downstream H2O2 targets comprise receptor kinases (like AtHPCA1) that activate channels allowing Ca+2 entry into the cytosol. Ca+2 will directly stimulate RBOH activity via its EF hands or indirectly through the activation of CCaMK (OsDMI3) that phosphorylates Ser-191 in OsRBOHB and further enhance RBOH activity to produce a second and sustained ABA-induced H2O2 burst. H2O2 can also contribute to enhance RBOH activity by oxidizing cysteins in clue inhibitors of ABA signaling, thus conforming additional amplification loops. H2O2 entering the cell through aquaporins (AQP) can oxidize clade K PP2Cs (OsPP45), releasing the inhibition of OsDMI3. In addition, H2O2 can oxidize thiol peroxidase PRXIIB, which forms a disulfide bridge with and inhibits clade A PP2Cs (AtABI2). Inhibition of these phosphatases allows further activation of SnRK2s to enhance downstream signaling, including phosphorylation of RBOH at Ser-140. These various positive feedback loops will augment H2O2 (and Ca+2) signaling to enhance ABA responses. Crosses indicate loss of inhibition of signaling components by ABA (blue) or H2O2 (red) that amplify signaling."
Authors: Ping-Xia Zhao and Chengbin Xiang.
bioRxiv (2023)
Abstract: "Lateral roots (LRs) are crucial for plants to sense environmental signals in addition to nutrient absorption. Auxin is a key regulator of LR formation, but the underlying intricate mechanisms are not fully understood. Here, we report that Arabidopsis ERF1, a hub transcription factor in the stress response, inhibits LR emergence by regulating local auxin accumulation with altered distribution as well as auxin signaling. ERF1 is expressed in the LR primordia (LRP) and induced by abiotic stresses and nutrient deficiency. Loss-of-function of ERF1 increases LR number and density compared with the wild type, whereas ERF1 overexpression lines exhibit the opposite phenotype. ERF1 enhances auxin acropetal and basipetal transport by directly upregulating the expression of PIN1 and AUX1, resulting in excessive auxin accumulation with altered distribution in the endodermis, cortex, and epidermis, which overlaps the region of new primordia emergence and leads to inhibition of LR emergence. Furthermore, ERF1 is involved in auxin signaling to regulate LR emergence by repressing ARF7 transcription, consequently affecting the expression of cell wall remodeling (CWR) genes facilitating LR emergence. Our results of biochemical, molecular, and genetic analyses further show that ERF1 directly regulates PIN1, AUX1, and ARF7 by binding to their promoters. Taken together, our study reveals that ERF1 promotes local auxin accumulation with altered distribution to inhibit LR emergence, acting as an important node integrating various stress signals into auxin signaling and thereby regulating LR formation in adaptation to fluctuating environments."
Authors: Peng Wang, Ning Wan, Walter J. Horst and Zhong-Bao Yang.
Journal of Experimental Botany (2023)
Abstract: "Aluminium (Al) toxicity is one of the major constraints for crop growth and productivity in most of the acid soils worldwide. The primary lesion of Al toxicity is the rapid inhibition of root elongation. The root apex, especially the transition zone (TZ), has been identified as the major Al accumulation and injury site. The signalling especially through phytohormones in the root apex TZ in response to Al stress has been reported to play crucial roles in the regulation of Al-induced root growth inhibition. The binding of Al in the root apoplast is the initial event leading to inhibition of root elongation. Much progress has been made during recent years in understanding the molecular functions of cell wall-modification and Al resistance-related genes in Al resistance or toxicity, and several signals including phytohormones, Ca 2+, etc. have been reported to be involved in these processes. Here we summarize the recent advances in the understanding of Al-induced signalling and regulatory networks in the root apex involved in the regulation of Al-induced inhibition of root growth and Al toxicity/resistance. This knowledge provides novel insights into how Al-induced signals are recognized by root apical cells, transmitted from apoplast to symplast, and finally initiated the defense system against Al. We conclude that the apoplast plays a decisive role in sensing and transmitting the Al-induced signals into the symplast, further stimulating a series of cellular responses (i.g. organic acid anions exudation from roots) to adapt to the stress, and we expect to stimulate new research by more clearly focusing on the signalling events in the root apex in response to Al stress particularly taking the signal transduction between meristem zone (MZ), TZ and elongation zone (EZ) and the apoplast and symplast into consideration."
Authors: Nils Kalbfuß, Alexander Strohmayr, Marcel Kegel, Lien Le, Friederike Grosseholz, Barbara Brunschweiger, Katharina Stöckl, Christian Wiese, Carina Franke, Caroline Schiestl, Sophia Prem, Shuyao Sha, Katrin Franz-Oberdorf, Juliane Hafermann, Marc Thiemé, Eva Facher, Wojciech Palubicki, Cordelia Bolle and Farhah F. Assaad.
bioRxiv (2022)
Abstract: "Plants often adapt to adverse conditions via differential growth, whereby limited resources are discriminately allocated to optimize the growth of one organ at the expense of another. Little is known about the decision-making processes that underly differential growth. In this study, we developed a screen to identify decision making mutants by deploying two tools that have been used in decision theory: a well-defined yet limited budget, as well as conflict-of-interest scenarios. A forward genetic screen that combined light and water withdrawal was carried out. This identified BRASSINOSTEROID INSENSITIVE 2 (BIN2) alleles as decision mutants with "confused" phenotypes. An assessment of organ and cell length suggested that hypocotyl elongation occurred predominantly via cellular elongation. In contrast, root growth appeared to be regulated by a combination of cell division and cell elongation or exit from the meristem. Brassinosteroid signalling mutants were most severely impaired in their ability to adjust cell geometry in the hypocotyl and cell elongation as a function of distance from the quiescent centre in the root tips. This study describes a novel paradigm for root growth under limiting conditions, which depends not only on hypocotyl-versus-root trade-offs in the allocation of limited resources, but also on an ability to deploy different strategies for root growth in response to multiple stress conditions."
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