Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Anshika Tyagi, Sajad Ali, Goriparthi Ramakrishna, Anupam Singh, Suvin Park, Henda Mahmoudi and Hanhong Bae.

Journal of Plant Growth Regulation (2023)

Abstract: "Phytohormone-like plant growth regulators are becoming hallmarks in plant stress biology since they can offer incredible benefits to plants, such as increased crop output, improved growth features and stress tolerance. Among them polyamines (PAs) such as putrescine (Put), spermidine (Spd), and spermine (Spm), are recognized as important bio-stimulants that can boost plant growth, productivity, and stress tolerance, whether provided exogenously or synthesized endogenously by genetically engineered plants. However, the precise mechanism by which they regulate plant development and stress responses and their interactions with other signaling molecules remains unknown. Hence, unravelling the molecular complexity of PAs signaling in plants can help us to improve crop stress resistance and yield. This review focuses on the distribution, biosynthesis, and role of PAs in plant growth and development, abiotic stress tolerance, and the involvement of a possible novel interlinked signaling cascade between them. Further, we focused on our current understanding and knowledge gaps of how PAs interact with other signaling molecules like hormones and nitric oxide (NO) to regulate plant growth and stress tolerance in a coordinated manner. We also provide an overview of PA signaling in plants, focusing on calcium (Ca2+) and reactive oxygen species (ROS) under abiotic stress, and some key insights into omics and nanotechnology approach for future research."

Authors: Ya Wang, Dongsheng Yu, Hongmiao Zhao, Lanlan Jiang, Lei Gao, Yanan Song, Zebin Liu, Fang bao, Congcong Hou, Yikun He, Chuanli Ju, Legong Li and Dongdong Kong.

Plant Signaling & Behavior (2022)

Abstract: "Plant glutamate receptor homologs (GLRs), which function as key calcium channels, play pivotal roles in various developmental processes as well as stress responses. The moss Physcomitrium patens, a representative of the earliest land plant lineage, possess multiple pathways of hormone signaling for coordinating growth and adaptation responses. However, it is not clear whether GLRs are connected to hormone-mediated growth control in the moss. In this study, we report that one of the two GLRs in P. patens, PpGLR1, involves in abscisic acid (ABA)-mediated growth regulation. ABA represses the growth of wild-type moss, and intriguingly, the PpGLR1 transcript levels are significantly increased in response to ABA treatment, based on both gene expression and the PpGLR1pro::GUS reporter results. Furthermore, the growth of Ppglr1 knockout moss mutants is hypersensitive to ABA treatment. These results suggest that PpGLR1 plays a critical role in ABA-mediated growth regulation, which provide useful information for our further investigation of the regulatory mechanism between Ca2+ signal and ABA in moss growth control."

Authors: Qifei Gao, Chao Wang, Yasheng Xi, Qiaolin Shao, Legong Li and Sheng Luan

Nature (2022)

One-sentence summary: The molecular mechanism by which FERONIA, LORELEI and NORTIA work together to facilitate calcium-mediated synergid–pollen tube communication in flowering plants is presented.

Abstract: "Precise signalling between pollen tubes and synergid cells in the ovule initiates fertilization in flowering plants1. Contact of the pollen tube with the ovule triggers calcium spiking in the synergids2,3 that induces pollen tube rupture and sperm release. This process, termed pollen tube reception, entails the action of three synergid-expressed proteins in Arabidopsis: FERONIA (FER), a receptor-like kinase; LORELEI (LRE), a glycosylphosphatidylinositol-anchored protein; and NORTIA (NTA), a transmembrane protein of unknown function4–6. Genetic analyses have placed these three proteins in the same pathway; however, it remains unknown how they work together to enable synergid–pollen tube communication. Here we identify two pollen-tube-derived small peptides7 that belong to the rapid alkalinization factor (RALF) family8 as ligands for the FER–LRE co-receptor, which in turn recruits NTA to the plasma membrane. NTA functions as a calmodulin-gated calcium channel required for calcium spiking in the synergid. We also reconstitute the biochemical pathway in which FER–LRE perceives pollen-tube-derived peptides to activate the NTA calcium channel and initiate calcium spiking, a second messenger for pollen tube reception. The FER–LRE–NTA trio therefore forms a previously unanticipated receptor–channel complex in the female cell to recognize male signals and trigger the fertilization process." 

Authors: Kenan Jia, Wei Wang, Qing Zhang and Wensuo Jia.

International Journal of Molecular Sciences (2023)

Abstract: "Plant cell walls are essential structures for plant growth and development as well as plant adaptation to environmental stresses. Thus, plants have evolved signaling mechanisms to monitor the changes in the cell wall structure, triggering compensatory changes to sustain cell wall integrity (CWI). CWI signaling can be initiated in response to environmental and developmental signals. However, while environmental stress-associated CWI signaling has been extensively studied and reviewed, less attention has been paid to CWI signaling in relation to plant growth and development under normal conditions. Fleshy fruit development and ripening is a unique process in which dramatic alternations occur in cell wall architecture. Emerging evidence suggests that CWI signaling plays a pivotal role in fruit ripening. In this review, we summarize and discuss the CWI signaling in relation to fruit ripening, which will include cell wall fragment signaling, calcium signaling, and NO signaling, as well as Receptor-Like Protein Kinase (RLKs) signaling with an emphasis on the signaling of FERONIA and THESEUS, two members of RLKs that may act as potential CWI sensors in the modulation of hormonal signal origination and transduction in fruit development and ripening."

Authors: Huihuang Chen, Lanxin Li, Linlin Qi and Jiri Friml.

bioRxiv (2023)

Abstract: "Auxin is the major plant hormone regulating growth and development (Friml, 2022). Forward genetic approaches in the model plant Arabidopsis thaliana have identified major components of auxin signalling and established the canonical mechanism mediating transcriptional and thus developmental reprogramming. In this textbook view, TRANSPORT INHIBITOR RESPONSE 1 (TIR1)/AUXIN-SIGNALING F-BOX (AFBs) are auxin receptors, which act as F-box subunits determining the substrate specificity of the Skp1-Cullin1-F box protein (SCF) type E3 ubiquitin ligase complex. Auxin acts as a molecular glue increasing the affinity between TIR1/AFBs and the Aux/IAA repressors. Subsequently, Aux/IAAs are ubiquitinated and degraded, thus releasing auxin transcription factors from their repression making them free to mediate transcription of auxin response genes (Yu et al., 2022). Nonetheless, accumulating evidence suggests existence of rapid, non-transcriptional responses downstream of TIR1/AFBs such as auxin-induced cytosolic calcium (Ca2+) transients, plasma membrane depolarization and apoplast alkalinisation, all converging on the process of root growth inhibition and root gravitropism (Li et al., 2022). Particularly, these rapid responses are mostly contributed by predominantly cytosolic AFB1, while the long-term growth responses are mediated by mainly nuclear TIR1 and AFB2-5 (Li et al., 2021; Prigge et al., 2020; Serre et al., 2021). How AFB1 conducts auxin-triggered rapid responses and how it is different from TIR1 and AFB2-5 remains elusive. Here, we compare the roles of TIR1 and AFB1 in transcriptional and rapid response by modulating their subcellular localization and testing their ability to mediate transcriptional responses in yeast."

Authors: Qifei Gao, Chao Wang, Yasheng Xi, Qiaolin Shao, Congcong Hou, Legong Li and Sheng Luan.

Cell Research (2023)

Abstract: "Pollen tube tip growth requires intricate Ca2+ signaling. Recent studies have also identified rapid alkalization factor (RALF)-family peptides and their receptors as critical components for pollen tube tip growth and integrity. The functional relationship of RALF and calcium signaling modules remains largely unclear. Here we report that disruption of RALF signaling pathway abolished the cytosolic Ca2+ gradient in the pollen tube, indicating that Ca2+ signaling is downstream of the RALF signaling pathway. We identified MILDEW RESISTANCE LOCUS O (MLO) family proteins MLO1, 5, 9, 15, as Ca2+ channels required for Ca2+ influx and pollen tube integrity. We further reconstituted the biochemical pathway in which signaling via RALF and RALF receptors activated MLO1/5/9/15 calcium channels. Together, we conclude that RALF peptides derived from pollen tube bind to their receptors to establish pollen tube Ca2+ gradient through activation of the MLO channels. Our finding has thus provided a mechanistic link between the RALF signaling pathway and Ca2+ signaling in controlling pollen tube integrity and growth."

Authors: Nelson B.C. Serre, Daša Wernerová, Pruthvi Vittal, Shiv Mani Dubey, Eva Medvecká, Adriana Jelínková, Jan Petrášek, Guido Grossmann and Matyáš Fendrych.

bioRxiv (2022)

Abstract: "Plant roots navigate in the dark soil environments following the gravity vector. Cell divisions in the meristem and rapid cell growth in the elongation zone propel the root tips through the soil. Actively elongating cells acidify their apoplast to enable cell wall extension by the activity of plasma membrane AHA H+-ATPases. The phytohormone auxin, central regulator of gravitropic response and root development, inhibits root cell growth, likely by rising the pH of the apoplast. However, the role of auxin in the regulation of the apoplastic pH gradient along the root tip is unclear. Here we show, by using an improved method for visualization and quantification of root surface pH, that the Arabidopsis thaliana root surface pH shows distinct acidic and alkaline zones, which are not primarily determined by the activity of AHA H+-ATPases. Instead, the distinct domain of alkaline pH in the root transition zone is controlled by a rapid auxin response module, consisting of the AUX1 auxin influx carrier, the AFB1 auxin co-receptor and the CNCG14 calcium channel. We demonstrate that the rapid auxin response pathway is required for an efficient navigation of the root tip."

Authors: Heike Seybold, Jennifer Bortlik, Xiyuan Jiang, Anja Liese, Benjamin Conrads, Wolfgang Hoehenwarter, Susanne Matschi and Tina Romeis.

bioRxiv (2022)

Abstract: "In nature plants are constantly challenged by simultaneous abiotic and biotic stresses, and under conflicting stress scenarios prioritization of stress responses is required for plant survival. Calcium-dependent protein kinase CPK5 is a central hub in local and distal immune signaling, required for hormone salicylic acid (SA)-dependent immunity and pathogen resistance. Here we show that CPK5-dependent immune responses and pathogen resistance are inhibited upon abscisic acid (ABA) treatment or in genetic mutant backgrounds lacking PP2C phosphatase activities including abi1-2, whereas immune responses are enhanced by co-expression of active ABI1 phosphatase variants. Biochemical studies and mass spectrometry-based phospho-site analysis reveal a direct ABI1 phosphatase-catalyzed de-phosphorylation of CPK5 auto-phosphorylation site T98. Mimicking continuous de-phosphorylation in CPK5T98A leads to enhanced ROS production and more resistant plants, mimicking the auto-phosphorylated status in CPK5T98D, reduces CPK5-mediated immune responses. Mechanistic insight identifies differential phosphorylation at T98 in the N-terminal domain of CPK5 to control the level of interaction between the kinase and its substrate protein rather than CPK5 catalytic activity. Thus, CPK5-catalyzed immune signaling may become discontinued even at an elevated cytoplasmic calcium concentration. Our work reveals an elegant mechanism for stress response prioritization in plants: The ABA-dependent phosphatase ABI1, negative regulator of abiotic responses, functions as positive regulator of biotic stress responses, stabilizing CPK5-dependent immune signaling in the absence of ABA. Continuous pathogen survey activates plant immunity in environmentally friendly conditions, whereas under severe abiotic stress the phosphatase/kinase pair prohibits immune signaling through a direct biochemical switch involving two key regulatory enzymes of these antagonistic pathways."

Authors: Takuma Hagihara, Hiroaki Mano, Tomohiro Miura, Mitsuyasu Hasebe and Masatsugu Toyota.

Nature Communications (2022)

Editor's view: Mimosa pudica moves its leaves within seconds of being touched or wounded. Here the authors show that such movements are triggered by rapid changes in Ca2+ and action and variation potentials and provide evidence that rapid movements help protect the plant from insect attacks.

Abstract: "Animals possess specialized systems, e.g., neuromuscular systems, to sense the environment and then move their bodies quickly in response. Mimosa pudica, the sensitive plant, moves its leaves within seconds in response to external stimuli; e.g., touch or wounding. However, neither the plant-wide signaling network that triggers these rapid movements nor the physiological roles of the movements themselves have been determined. Here by simultaneous recording of cytosolic Ca2+ and electrical signals, we show that rapid changes in Ca2+ coupled with action and variation potentials trigger rapid movements in wounded M. pudica. Furthermore, pharmacological manipulation of cytosolic Ca2+ dynamics and CRISPR-Cas9 genome editing technology revealed that an immotile M. pudica is more vulnerable to attacks by herbivorous insects. Our findings provide evidence that rapid movements based on propagating Ca2+ and electrical signals protect this plant from insect attacks."