Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: R. B. Lima and D. D. Figueiredo.

Plant and Cell Physiology (2024)

Abstract: "Since the discovery of brassinolide in the pollen of rapeseed, brassinosteroids (BRs) have consistently been associated with reproductive traits. However, compared to what is known for how BRs shape vegetative development, the understanding of how these hormones regulate reproductive traits is comparatively still lacking. Nevertheless, there is now considerable evidence that BRs regulate almost all aspects of reproduction, from ovule and pollen formation to seed and fruit development. Here, we review the current body of knowledge on how BRs regulate reproductive processes in plants, and what is known about how these pathways are transduced at the molecular level. We then discuss how the manipulation of BR biosynthesis and signaling can be a promising avenue for improving crop traits which rely on efficient reproduction. We thus propose that BR hold an untapped potential for plant breeding, which could contribute to attain food security in the coming years."

Authors: Irene Rosa-Díaz, James Rowe, Ana Cayuela-Lopez, Vicent Arbona, Isabel Díaz and Alexander M. Jones.

Plant Physiology (2024)

One-sentence summary: Arabidopsis thaliana employs abscisic acid–induced stomatal closure as an effective defense mechanism against Tetranychus urticae infestation.

Abstract: "Arthropod herbivory poses a serious threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest two-spotted spider mite (Tetranychus urticae) inflicts rapid damage and remains challenging due to its broad target range. In this study, we explored the Arabidopsis (Arabidopsis thaliana) response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, and stomatal closure during water stress. Leveraging a FRET-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types post-mite feeding. While ABA's role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation alongside intact canonical biotic stress signaling, indicating an independent function of ABA in mite defense. We established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage through genetic and pharmacological interventions targeting ABA levels, ABA signaling, stomatal aperture, and density. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, reinforces the intricate relationship between these stress types."

Authors: Kalyan Mahapatra, Shubhi Dwivedi, Arpan Mukherjee, Ajar Anupam Pradhan, Kavuri Venkateswara Rao, Deeksha Singh, Lavanya Bhagavatula and Sourav Datta.

Journal of Experimental Botany (2024)

Abstract: "The exogenous light cues and the phytohormone Abscisic acid (ABA) regulate several aspects of plant growth and development. In recent years, the role of the crosstalk between the light and ABA signaling pathways in regulating different physiological processes has become increasingly evident. This includes the regulation of germination and early seedling development, control of stomatal development and conductance, growth and development of roots, buds, branches, and regulation of flowering. Light and ABA signaling cascades have various convergence points at both DNA and protein levels. The molecular crosstalk involves several light signaling factors like HY5, COP1, PIFs and BBXs that integrate with ABA signaling components like the PYL receptors and ABI5. Especially, ABI5 and PIF4 promoters serve as key “hotspots” for the integration of these two pathways. Plants acquired both light and ABA signaling pathways before they colonized land almost 500 million years ago. In this review, we discuss the recent advances in the interplay of light and ABA signaling regulating plant development and provide an overview of the evolution of these two pathways."

Author: Leiyun Yang

The Plant Cell (2024)

Excerpts: "Simultaneously, low temperature stimulates plant immunity by activating salicylic acid (SA)-mediated signaling (Wu et al. 2019). However, the mechanism by which plants integrate cold signals and immune signaling remain elusive. To investigate this question, Shaoqin Li and colleagues (Li et al. 2024) studied the potential involvement of ICE1 in cold-induced immunity in Arabidopsis."

"To elucidate how ICE1 regulates cold-induced immunity, the authors conducted a yeast-two-hybrid screen and identified NON-EXPRESSER OF PR GENES 1 (NPR1), a master transcriptional co-activator of PATHOGENESIS-RELATED GENE 1 (PR1) in SA-activated immunity, as an ICE1 interactor.....Additionally, the authors found that ICE1 directly binds to the PR1 promoter for gene activation. These results illustrate that ICE1 interacts with NPR1 and is required for SA-mediated immunity by directly promoting PR1 expression."

"These results support the conclusion that ICE1 and TGA3 work synergistically to promote PR1 transcription. This study not only shed light on a new role of ICE1 in SA-mediated immunity at low temperature, but also revealed NPR1-TGA3/ICE1 as an important nexus integrating SA signaling and cold signals in plant immunity (see Figure)."

Authors: Tomoaki Sakamoto, Shuka Ikematsu, Hokuto Nakayama, Terezie Mandáková, Gholamreza Gohari, Takuya Sakamoto, Gaojie Li, Hongwei Hou, Sachihiro Matsunaga, Martin A. Lysak and Seisuke Kimura

Communications Biology (2024)

One-sentence summary: A chromosome-level genome assembly for the amphibious plant Rorippa aquatica uncovers its tetraploid origin and an involvement of ethylene in heterophylly upon submergence.

Abstract: "The ability to respond to varying environments is crucial for sessile organisms such as plants. The amphibious plant Rorippa aquatica exhibits a striking type of phenotypic plasticity known as heterophylly, a phenomenon in which leaf form is altered in response to environmental factors. However, the underlying molecular mechanisms of heterophylly are yet to be fully understood. To uncover the genetic basis and analyze the evolutionary processes driving heterophylly in R. aquatica, we assembled the chromosome-level genome of the species. Comparative chromosome painting and chromosomal genomics revealed that allopolyploidization and subsequent post-polyploid descending dysploidy occurred during the speciation of R. aquatica. Based on the obtained genomic data, the transcriptome analyses revealed that ethylene signaling plays a central role in regulating heterophylly under submerged conditions, with blue light signaling acting as an attenuator of ethylene signal. The assembled R. aquatica reference genome provides insights into the molecular mechanisms and evolution of heterophylly."

Authors: Verónica Sánchez-Gerschon, Irene Martínez-Fernández, María R. González-Bermúdez, Sergio de la Hoz-Rodríguez, Florenci V. González, Jorge Lozano-Juste, Cristina Ferrándiz and Vicente Balanzà.

Plant Physiology (2024)

One-sentence summary: Three homeodomain leucine zipper transcription factors trigger abscisic acid accumulation in the inflorescence apex at the end of the reproductive phase, arresting unpollinated floral bud development.

Abstract: "Flowers, and hence, fruits and seeds, are produced by the activity of the inflorescence meristem after the floral transition. In plants with indeterminate inflorescences the final number of flowers produced by the inflorescence meristem is determined by the length of the flowering period, which ends with inflorescence arrest. Inflorescence arrest depends on many different factors, such as the presence of seeds, the influence of the environment, or endogenous factors such as phytohormone levels and age, which modulate inflorescence meristem activity. The FRUITFULL-APETALA2 (FUL-AP2) pathway plays a major role in regulating the end of flowering, likely integrating both endogenous cues and those related to seed formation. Among AP2 targets, HOMEOBOX PROTEIN21 (HB21) has been identified as a putative mediator of AP2 function in the control of inflorescence arrest. HB21 is a homeodomain leucine zipper transcription factor involved in establishing axillary bud dormancy. Here we characterized the role of HB21 in the control of the inflorescence arrest at the end of flowering in Arabidopsis (Arabidopsis thaliana). HB21, together with HB40 and HB53, are upregulated in the inflorescence apex at the end of flowering, promoting floral bud arrest. We also show that abscisic acid (ABA) accumulation occurs in the inflorescence apex in an HB-dependent manner. Our work suggests a physiological role of ABA in floral bud arrest at the end of flowering, pointing to ABA as a regulator of inflorescence arrest downstream of the HB21/40/53 genes."

Authors: Yiran Xu, Shengdong Qi, Yong Wang and Jingbo Jia.

Journal of Experimental Botany (2024)

One-sentence summary: This review summarizes the interplay between nitrate and abscisic acid and provides research perspectives for breeding high nitrogen use efficiency and stress-tolerant crop varieties.

Abstract: "To meet the demands of the new Green Revolution and sustainable agriculture, it is important to develop crop varieties with improved yield, nitrogen use efficiency, and stress resistance. Nitrate is the major form of inorganic nitrogen available for plant growth in many well-aerated agricultural soils, and acts as a signaling molecule regulating plant development, growth, and stress responses. Abscisic acid (ABA), an important phytohormone, plays vital roles in integrating extrinsic and intrinsic responses and mediating plant growth and development in response to biotic and abiotic stresses. Therefore, elucidating the interplay between nitrate and ABA can contribute to crop breeding and sustainable agriculture. Here, we review studies that have investigated the interplay between nitrate and ABA in root growth modulation, nitrate and ABA transport processes, seed germination regulation, and drought responses. We also focus on nitrate and ABA interplay in several reported omics analyses with some important nodes in the crosstalk between nitrate and ABA. Through these insights, we proposed some research perspectives that could help to develop crop varieties adapted to a changing environment and to improve crop yield with high nitrogen use efficiency and strong stress resistance."

Authors: Minmin He, Gui Geng, Shuyang Mei, Gang Wang, Lihua Yu, Yao Xu and Yuguang Wang.

Functional Plant Biology (2024)

Abstract: "Water stress (drought and waterlogging) leads to an imbalance in plant water distribution, disrupts cell homeostasis, and severely inhibits plant growth. Melatonin is a growth hormone that plants synthesise and has been shown to resist adversity in many plants. This review discusses the biosynthesis and metabolism of melatonin, as well as the changes in plant morphology and physiological mechanisms caused by the molecular defence process. Melatonin induces the expression of related genes in the process of plant photosynthesis under stress and protects the structural integrity of chloroplasts. Exogenous melatonin can maintain the dynamic balance of root ion exchange under waterlogging stress. Melatonin can repair mitochondria and alleviate damage caused by reactive oxygen species and reactive nitrogen species; and has a wide range of uses in the regulation of stress-specific genes and the activation of antioxidant enzyme genes. Melatonin improves the stability of membrane lipids in plant cells and maintains osmotic balance by regulating water channels. There is crosstalk between melatonin and other hormones, which jointly improve the ability of the root system to absorb water and breathe and promote plant growth. Briefly, as a multifunctional molecule, melatonin improves the tolerance of plants under water stress and promotes plant growth and development."

Authors: María Isabel Puga, César Poza-Carrión, Iris Martinez-Hevia, Laura Perez-Liens and Javier Paz-Ares

Journal of Plant Research (2024)

Abstract: "Phosphorus is indispensable for plant growth and development, with its status crucial for determining crop productivity. Plants have evolved various biochemical, morphological, and developmental responses to thrive under conditions of low P availability, as inorganic phosphate (Pi), the primary form of P uptake, is often insoluble in soils. Over the past 25 years, extensive research has focused on understanding these responses, collectively forming the Pi starvation response system. This effort has not only expanded our knowledge of strategies to cope with Pi starvation (PS) but also confirmed their adaptive significance. Moreover, it has identified and characterized numerous components of the intricate regulatory network governing P homeostasis. This review emphasizes recent advances in PS signaling, particularly highlighting the physiological importance of local PS signaling in inhibiting primary root growth and uncovering the role of TORC1 signaling in this process. Additionally, advancements in understanding shoot-root Pi allocation and a novel technique for studying Pi distribution in plants are discussed. Furthermore, emerging data on the regulation of plant-microorganism interactions by the PS regulatory system, crosstalk between the signaling pathways of phosphate starvation, phytohormones and immunity, and recent studies on natural variation in Pi homeostasis are addressed.

Authors: Martijn de Roij, Jan Willem Borst and Dolf Weijers.

The Plant Cell (2024)

One-sentence summary: The authors review the deeply intertwined roles of proteolytic regulation in the auxin response.

Abstract: "The signaling molecule auxin sits at the nexus of plant biology and coordinates essentially all growth and developmental processes in plants. Auxin molecules are transported throughout plant tissues and are capable of evoking highly specific physiological responses in plant cells by inducing various molecular pathways. In many of these pathways, proteolysis plays a crucial role for correct physiological responses. This review provides a chronology of the discovery and characterisation of the auxin receptor, which is a fascinating example of separate research trajectories ultimately converging on the discovery of a core auxin signaling hub which relies on degradation of a family of transcriptional inhibitor proteins – the Aux/IAAs. Beyond describing the “classical” proteolysis-driven auxin response system, we explore more recent examples of the interconnection of proteolytic systems, which target a range of other auxin signaling proteins, and auxin response. By highlighting these emerging concepts, we provide potential future directions to further investigate the role of protein degradation within the framework of auxin response."

Authors: Changxia Li, Xuemei Hou, Zongxi Zhao, Huwei Liu, Panpan Huang, Meimei Shi, Xuetong Wu, Rong Gao, Zhiya Liu, Lijuan Wei, Yihua Li and Weibiao Liao.

Cellular & Molecular Biology Letters (2024)

Abstract: "In tomato (Solanum lycopersicum), the ripening of fruit is regulated by the selective expression of ripening-related genes, and this procedure is controlled by transcription factors (TFs). In the various plant-specific TF families, the no apical meristem (NAM), Arabidopsis thaliana activating factor 1/2 (ATAF1/2), and cup-shaped cotyledon 2 (CUC2; NAC) TF family stands out and plays a significant function in plant physiological activities, such as fruit ripening (FR). Despite the numerous genes of NAC found in the tomato genome, limited information is available on the effects of NAC members on FR, and there is also a lack of studies on their target genes. In this research, we focus on SlNAP1, which is a NAC TF that positively influences the FR of tomato. By employing CRISPR/Cas9 technology, compared with the wild type (WT), we generated slnap1 mutants and observed a delay in the ethylene production and color change of fruits. We employed the yeast one-hybrid (Y1H) and dual-luciferase reporter (DLR) assays to confirm that SlNAP1 directly binds to the promoters of two crucial genes involved in gibberellin (GA) degradation, namely SlGA2ox1 and SlGA2ox5, thus activating their expression. Furthermore, through a yeast two-hybrid (Y2H), bimolecular fluorescence complementation (BIFC) and luciferase (LUC) assays, we established an interaction between SlNAP1 and SlGID1. Hence, our findings suggest that SlNAP1 regulates FR positively by activating the GA degradation genes directly. Additionally, the interaction between SlNAP1 and SlGID1 may play a role in SlNAP1-induced FR. Overall, our study provides important insights into the molecular mechanisms through which NAC TFs regulate tomato FR via the GA pathway."

Authors: Jihua Ding, Kejing Wang, Shashank Pandey, Mariano Perales, Isabel Allona, Md Rezaul Islam Khan, Victor B. Busov, Rishikesh P. Bhalerao

Journal of Experimental Botany (2024)

Abstract: "Seasonal bud dormancy in perennial woody plants is a crucial and intricate process that is vital for the survival and development of plants. Over the past few decades, significant advancements have been made in understanding many features of bud dormancy, particularly in model species, where certain molecular mechanisms underlying this process have been elucidated. In this review, we provide an overview of recent molecular progress in understanding bud dormancy in trees, with a specific emphasis on the integration of common signaling and molecular mechanisms identified across different tree species. Additionally, we address some challenges that have emerged in the in-depth understanding of bud dormancy and offer insights for future studies."