Plant hormones (Literature sources on phytohormones and plant signalling)

Authors: Huibin Wang, Shichao Zhang, Yingying Qu, Rui Gao, Yuxiong Xiao, Zhigang Wang, Rui Zhai, Chengquan Yang and Lingfei Xu.

International Journal of Molecular Sciences (2021)

Abstract: "Seedless fruit is a feature appreciated by consumers. The ovule abortion process is highly orchestrated and controlled by numerous environmental and endogenous signals. However, the mechanisms underlying ovule abortion in pear remain obscure. Here, we found that gibberellins (GAs) have diverse functions during ovules development between seedless pear ‘1913’ and seeded pear, and that GA4+7 activates a potential programmed cell death process in ‘1913’ ovules. After hormone analyses, strong correlations were determined among jasmonic acid (JA), ethylene and salicylic acid (SA) in seedless and seeded cultivars, and GA4+7 treatments altered the hormone accumulation levels in ovules, resulting in significant correlations between GA and both JA and ethylene. Additionally, SA contributed to ovule abortion in ‘1913’. Exogenously supplying JA, SA or the ethylene precursor 1-aminocyclopropane-1-carboxylic acid promoted ‘Bartlett’ seed death. The regulatory mechanism in which ethylene controls ovule death has been demonstrated; therefore, JA’s role in regulating ‘1913’ ovule abortion was investigated. A further study identified that the JA signaling receptor MYC2 bound the SENESCENCE-ASSOCIATED 39 promoter and triggered its expression to regulate ovule abortion. Thus, we established ovule abortion-related relationships between GA and the hormones JA, ethylene and SA, and we determined their synergistic functions in regulating ovule death."

Authors: Justine Bresson, Jasmin Doll, Francois Vasseur, Mark Stahl, Edda von Roepenack-Lahaye, Joachim Kilian, Bettina Stadelhofer, James M. Kremer, Dagmar Kolb, Stephan Wenkel and Ulrike Zentgraf.

bioRxiv (2021)

Abstract: "In annual plants, tight coordination of successive developmental events is of primary importance to optimize performance under fluctuating environmental conditions. The recent finding of the genetic interaction of WRKY53 , a key senescence-related gene with REVOLUTA , a master regulator of early leaf patterning, raises the question of how early and late developmental events are connected. Here, we investigated the developmental and metabolic consequences of an alteration of the REVOLUTA and WRKY53 gene expression, from seedling to fruiting . Our results show that REVOLUTA critically controls late developmental phases and reproduction while inversely WRKY53 determines vegetative growth at early developmental stages. We further show that these regulators of distinct developmental phases frequently, but not continuously, interact throughout ontogeny and demonstrated that their genetic interaction is mediated by the salicylic acid (SA). Moreover, we showed that REVOLUTA and WRKY53 are keys regulatory nodes of development and plant immunity thought their role in SA metabolic pathways, which also highlights the role of REV in pathogen defence. Together, our findings demonstrate how late and early developmental events are tightly intertwined by molecular hubs. These hubs interact with each other throughout ontogeny, and participate to the interplay between plant development and immunity."

Authors: Olena Zamora, Sebastian Schulze, Tamar Azoulay-Shemer, Helen Parik, Jaanika Unt, Mikael Brosché, Julian I. Schroeder, Dmitry Yarmolinsky and Hannes Kollist.

The Plant Journal (2021)

Abstract: "Jasmonic acid (JA) and salicylic acid (SA) regulate stomatal closure, preventing pathogen invasion into plants. However, to which extent abscisic acid (ABA), SA, and JA interact and what the roles of SA and JA are in stomatal responses to environmental cues remains unclear. Here, by using intact plant gas-exchange measurements in JA and SA single and double mutants, we show that stomatal responsiveness to CO2, light intensity, ABA, high vapor pressure deficit, and ozone either did not or for some stimuli only very slightly depended on JA and SA biosynthesis and signaling mutants, including dde2, sid2, coi1, jai1, myc2, and npr1 alleles. While stomata in the studied mutants clearly responded to ABA, CO2, light, and ozone, ABA-triggered stomatal closure in npr1-1 was slightly accelerated comparing with the wild type. Stomatal re-opening after ozone pulses was quicker in the coi1-16 mutant than in the wild type. In intact Arabidopsis plants, spraying with methyl-JA led to only a modest reduction in stomatal conductance 80 min after the treatments, whereas ABA and CO2 induced pronounced stomatal closure within minutes. We could not document a reduction of stomatal conductance after spraying with SA. Coronatine-induced stomatal opening was initiated slowly after 1.5-2 h and reached a maximum in 3 h after spraying intact plants. Our results suggest that ABA, CO2 and light are major regulators of rapid guard cell signaling, whereas JA and SA could play only minor roles in whole-plant stomatal response to environmental cues in Arabidopsis and tomato."

Authors: Jian Wang, Xiaofen Liu, Wen-qiu Wang, Hui-qin Zhang and Xue-ren Yin.

bioRxiv (2021)

Abstract: "Levels of ethylene, implicated in a diverse array of plants for inducing fruit ripening, is influenced by genetic and environmental factors, such as the other plant hormones. Among these, salicylic acid (SA) has been demonstrated to inhibit ethylene biosynthesis in fruit, yet the underlying regulatory mechanisms remains elusive. Here, we showed that treatment with exogenous ASA (acetylsalicylic acid) dramatically reduced ethylene production, as well as activities of ACC synthase (ACS) and ACC oxidase (ACO), in kiwifruit tissues. Comparative transcriptome analysis indicated the differential expression of ethylene biosynthetic genes (AdACS1/2 and AdACO5). A screen of transcription factors indicated that AdERF105L and AdWRKY29 were ASA-responsive regulators of AdACS1/2 and AdACO5, respectively. In addition to these genes, AdACS3 and AdACO3 were abundantly expressed in both ASA-treated and control tissues. AdACS3 protein was phosphorylated and stabilized by AdMPK16, a mitogen-activated protein kinase; while AdACO3 activity was enhanced by AdAP, an aspartic peptidase. Exogenous ASA down-regulated AdMPK16 and AdAP, thereby influencing ethylene biosynthesis at a post-transcriptional level. These findings propose a multidimensional system for SA-inhibition on ethylene biosynthesis, inducing differential expression of some ethylene biosynthesis genes, as well as differential effects on protein activity on other targets."

Authors: Xiangyang Li, Mengmeng Liao, Jiayu Huang, Zheng Xu, Zhanqiao Lin, Nenghui Ye, Zhisheng Zhang and Xinxiang Peng.  

BMC Plant Biology (2021)

Abstract: "Background - Glycolate oxidase (GLO) is not only a key enzyme in photorespiration but also a major engine for H2O2 production in plants. Catalase (CAT)-dependent H2O2 decomposition has been previously reported to be involved in the regulation of IAA biosynthesis. However, it is still not known which mechanism contributed to the H2O2 production in IAA regulation. Results - In this study, we found that in glo mutants of rice, as H2O2 levels decreased IAA contents significantly increased, whereas high CO2 abolished the difference in H2O2 and IAA contents between glo mutants and WT. Further analyses showed that tryptophan (Trp, the precursor for IAA biosynthesis in the Trp-dependent biosynthetic pathway) also accumulated due to increased tryptophan synthetase β (TSB) activity. Moreover, expression of the genes involved in Trp-dependent IAA biosynthesis and IBA to IAA conversion were correspondingly up-regulated, further implicating that both pathways contribute to IAA biosynthesis as mediated by the GLO-dependent production of H2O2. Conclusion - We investigated the function of GLO in IAA signaling in different levels from transcription, enzyme activities to metabolic levels. The results suggest that GLO-dependent H2O2 signaling, essentially via photorespiration, confers regulation over IAA biosynthesis in rice plants."

Authors: Chunzhao Zhao, Wei Jiang, Omar Zayed, Xin Liu, Kai Tang, Wenfeng Nie, Yali Li, Shaojun Xie, Yuan Li, Tiandan Long, Linlin Liu, Yingfang Zhu, Yang Zhao and Jian-Kang Zhu.

National Science Review (2021)

Abstract. "Salt stress is a major environmental factor limiting plant growth and productivity. We recently discovered an important new salt tolerance pathway, where the cell wall leucine-rich repeat extensins LRX3/4/5, the RAPID ALKALINIZATION FACTOR (RALF) peptides RALF22/23 and receptor-like kinase FERONIA (FER) function as a module to simultaneously regulate plant growth and salt stress tolerance. However, the intracellular signaling pathways that are regulated by the extracellular LRX3/4/5-RALF22/23-FER module to coordinate growth, cell wall integrity and salt stress responses are still unknown. Here, we report that the LRX3/4/5-RALF22/23-FER module negatively regulates the levels of jasmonic acid (JA), salicylic acid (SA) and abscisic acid (ABA). Blocking JA pathway rescues the dwarf phenotype of the lrx345 and fer-4 mutants, while disruption of ABA biosynthesis suppresses the salt-hypersensitivity of these mutants. Many salt stress-responsive genes display abnormal expression patterns in the lrx345 and fer-4 mutants, as well as in the wild type plants treated with epigallocatechin gallate (EGCG), an inhibitor of pectin methylesterases, suggesting cell wall integrity as a critical factor that determines the expression pattern of stress-responsive genes. Production of reactive oxygen species (ROS) is constitutively increased in the lrx345 and fer-4 mutants, and inhibition of ROS accumulation suppresses the salt-hypersensitivity of these mutants. Together, our work provides strong evidence that the LRX3/4/5-RALF22/23-FER module controls plant growth and salt stress responses by regulating hormonal homeostasis and ROS accumulation."

Authors: Qiuping Liu, Ur Rehman Atta, Renfen Wang, Kexin Liu, Xia Ma and Qingbei Weng.

European Journal of Plant Pathology (2021)

Abstract: "Increasing evidence suggest that melatonin (N-acetyl-5-methoxytryptamine), an indolic compound identified from the pineal gland of mammals, regulates plant disease resistance. Here, we show that melatonin promoted susceptibility of salicylic acid (SA)-deficient Arabidopsis plants to the virulent bacterium Pseudomonas syringae, but enhanced resistance of jasmonic acid (JA)-insensitive mutants, ethylene (ET)-insensitive mutants, and abscisic acid (ABA)-biosynthetic mutants. However, melatonin had no effects on wild type Arabidopsis plants defending against P. syringae. In wild type Arabidopsis leaves, melatonin enabled to elevate endogenous SA and ABA levels and reduced JA and JA-isoleucine accumulation. In addition, melatonin induced the transcripts of SA-dependent pathogenesis-related protein 1 and JA/ET-dependent plant defensin 1.2. Furthermore, melatonin could affect neither pathogen-associated molecular pattern-triggered immunity nor avirulent effector-triggered immunity. Since ABA and JA/ET signaling antagonize SA-dependent disease resistance, our results thus clarify that defense-related hormone signaling, but not basal immune events, cooperatively determine the destiny of melatonin during Arabidopsis thaliana-P. syringae interaction."

Authors: Yujun Peng, Jianfei Yang, Xin Li and Yuelin Zhang.

Annual Review of Plant Biology (2021)

Abstract: "Salicylic acid (SA) is an essential plant defense hormone that promotes immunity against biotrophic and semibiotrophic pathogens. It plays crucial roles in basal defense and the amplification of local immune responses, as well as the establishment of systemic acquired resistance. During the past three decades, immense progress has been made in understanding the biosynthesis, homeostasis, perception, and functions of SA. This review summarizes the current knowledge regarding SA in plant immunity and other biological processes. We highlight recent breakthroughs that substantially advanced our understanding of how SA is biosynthesized from isochorismate, how it is perceived, and how SA receptors regulate different aspects of plant immunity. Some key questions in SA biosynthesis and signaling, such as how SA is produced via another intermediate benzoic acid and how SA affects the activities of its receptors in the transcriptional regulation of defense genes, remain to be addressed." 

Authors: Wenrui Gao, Yan Liu, Juan Huang, Yaqiu Chen, Chen Chen, Lu Lu, Hongwei Zhao, Shuzhen Men and Xiaoming Zhang.

Research Square (2021)

Abstract: "Seed germination is an important phase transitional period of angiosperm plants and sensitive to environment condition. Although seed germination is under the regulation of salicylic acid (SA) and other hormones, the molecular mechanism underlying these regulations remains mysterious. In this study, we determined the expression of SA methyl esterase (MES) family genes during seed germination. We found that MES7 expression decreases significantly in imbibed seeds, and the dysfunction of MES7 decreases SA content. Furthermore, MES7 reduces and promotes seed germination under normal and salt stress conditions, respectively. The application of SA restores the seed germination deficiencies of mes7 mutants under different conditions. Taking together, our observations uncover a MeSA hydrolyzation enzyme, MES7, regulates seed germination via altering SA titer under normal and abiotic stress conditions."

Authors: Yu Zhang, Ru-Feng Song, Hong-Mei Yuan, Ting-Ting Li, Lin-Feng Wang, Kai-Kai Lu, Jia-Xing Guo and Wen-Cheng Liu.

Molecular Plant Pathology (2021)

Abstract: "Salicylic acid (SA) acts antagonistically to jasmonic acid (JA) in plant immunity. We previously reported that CATALASE2 (CAT2) promotes JA-biosynthetic acyl-CoA oxidase (ACX) activity to enhance plant resistance to necrotrophic Botrytis cinerea, and SA represses JA biosynthesis through inhibiting CAT2 activity, while the underlying mechanism remains to be further elucidated. Here, we report that the truncated CAT2 N-terminus (CAT2-N) interacts with and promotes ACX2/3, and CAT2-N-overexpressing plants have increased JA accumulation and enhanced resistance to B. cinerea B05.10, but compromised antagonism of SA on JA. Catalase inhibitor treatment or mutating CAT2 active amino acids abolished CAT2 H2O2-decomposing activity but did not affect its promotion of ACX2/3 activity via interaction. CAT2-N, a truncated protein with no catalase activity, interacted with and promoted ACX2/3. Overexpressing CAT2-N in Arabidopsis plants resulted in increased ACX activity, higher JA accumulation, and stronger resistance to B. cinerea B05.10 infection. Additionally, SA dramatically repressed JA biosynthesis and resistance to B. cinerea in the wild type but not in the CAT2-N-overexpressing plants. Together, our study reveals that CAT2-N can be utilized as an accelerator for JA biosynthesis during plant resistance to B. cinerea B05.10, and this truncated protein partly relieves SA repression of JA biosynthesis in plant defence responses."

Authors: Kamran Shah, Na An, Svetlana Kamanova, Lijuan Chen, Peng Jia, Chenguang Zhang, Muhammad Mobeen Tahir, Mingyu Han, Yuduan Ding, Xiaolin Ren and Libo Xing.

Frontiers in Plant Science (2021)

Abstract: "In the external coincidence model, internal and external molecular signals, provided by the circadian clock and sunlight, respectively, are required to induce flowering. Salicylic acid (SA) applications during floral induction have multiple effects. In the current study, Malus × domestica plants were exposed to SA during the flower-induction stage to analyze the effect on various health markers and flowering. A total of 56 equal-sized Fuji/M9 trees that were about 7 years old were randomly divided into two groups. The first group (SA-treated) was sprayed with 4 mM SA solution, while the second group was sprayed with distilled water which served as control (CK). The SA applications increased various leaf pigments. Abiotic stress markers were increased in CK during the flower-induction stage. In the SA-treated group, non-enzymatic antioxidants increased, whereas in the control group, enzymatic antioxidants increased during the flower-induction stage. Histo-morphometric properties of leaves were significantly improved in the SA-treated group. The relative expression of the mRNA levels of MdMED80, −81, −3, and −41 were significantly increased in SA-treated leaves, leading to an early and increased flowering phenotype. Thus, SA increased leaf expansion and health-related marker levels, which lead to early induction of flowering in M. domestica. Overall, our work established a role for leaf health assessments in the regulation of flowering in M. domestica."

Authors: Yujun Peng, Jianfei Yang, Xin Li and Yuelin Zhang.

Annual Review of Plant Biology (2021)

Abstract: "Salicylic acid (SA) is an essential plant defense hormone that promotes immunity against biotrophic and semibiotrophic pathogens. It plays crucial roles in basal defense and the amplification of local immune responses, as well as the establishment of systemic acquired resistance. During the past three decades, immense progress has been made in understanding the biosynthesis, homeostasis, perception, and functions of SA. This review summarizes the current knowledge regarding SA in plant immunity and other biological processes. We highlight recent breakthroughs that substantially advanced our understanding of how SA is biosynthesized from isochorismate, how it is perceived, and how SA receptors regulate different aspects of plant immunity. Some key questions in SA biosynthesis and signaling, such as how SA is produced via another intermediate, benzoic acid, and how SA affects the activities of its receptors in the transcriptional regulation of defense genes, remain to be addressed."

Authors: Chunoti Changwal, Tushita Shukla, Zakir Hussain, Neera Singh, Abhijit Kar, Virendra P. Singh, M. Z. Abdin and Ajay Arora.

Frontiers in Plant Science (2021)

Abstract: "Exogenous application of salicylic acid (SA) has been known for delaying ripening in many fruit and vegetables. But the function of endogenous SA in relation to postharvest fruit performance is still unexplored. To understand the role of endogenous SA in postharvest fruit ripening of tomato, 33 tomato lines were examined for their endogenous SA content, membrane stability index (MSI), and shelf life (SL) at turning and red stages of tomato fruit ripening. Six tomato lines having contrasting shelf lives from these categories were subjected further for ethylene (ET) evolution, 1-aminocyclopropane-1-carboxylic acid synthase (ACS), 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), polygalacturonase (PG), pectin methyl esterase (PME), antioxidant assays and lipid peroxidation. It was found that high endogenous SA has a direct association with low ET evolution, which leads to the high SL of fruit. High lycopene content was also found to be correlated with high SA. Total antioxidants, PG, and PME decreased and lipid peroxidation increased from turning to red stage of tomato fruit development. Furthermore, these lines were subjected to expression analysis for SA biosynthesis enzymes viz. Solanum lycopersicum Isochorismate Synthase (SlICS) and SlPAL. Real-time PCR data revealed that high SL lines have high SlPAL4 expression and low SL lines have high SlPAL6 expression. Based on the results obtained in this study, it was concluded that endogenous SA regulates ET evolution and SL with the aid of the antioxidative defense system, and SlPAL4 and SlPAL6 genes play significant but opposite roles during fruit ripening."

Authors: Zong-You Lv, Wen-Jing Sun, Rui Jiang, Jun-Feng Chen, Xiao Ying, Lei Zhang and Wan-Sheng Chen.

World Journal of Traditional Chinese Medicine (2021)

Abstract: "Until recently, many studies on the role of phytohormones in plant secondary metabolism focused on jasmonic acid (JA), salicylic acid (SA), gibberellins (GA), and abscisic acid (ABA). It is now clear that phytohormone-induced regulation of signaling occurs via regulation of the biosynthetic pathway genes at the transcriptional level or through posttranslational regulation, or an increase in secondary metabolite deposition (e.g., trichomes). Here, we summarize recent advances, updating the current reports on the molecular machinery of phytohormones JA, SA, GA, and ABA involved in plant secondary metabolites. This review emphasizes the differences and similarities among the four phytohormones in regulating various secondary metabolic biosynthetic pathways and also provides suggestions for further research."

Authors: Zhiqian Li, Yuntong Jiao, Chen Zhang, Mengru Dou, Kai Weng, Yuejin Wang and Yan Xu.

Plant Biotechnology Journal (2021)

Abstract: "Seedlessness in grapes is one of the features most appreciated by consumers. However, the mechanisms underlying seedlessness in grapes remain obscure. Here, we observe small globular embryos and globular embryos in Pinot Noir and Thompson Seedless from 20 to 30 days after flowering (DAF). From 40 to 50 DAF, we observe torpedo embryos and cotyledon embryos in Pinot Noir but aborted embryos and endosperm in Thompson Seedless. Thus, RNA‐Seq analyses of seeds at these stages from Thompson Seedless and Pinot Noir were performed. A total of 6442 differentially expressed genes were identified. Among these, genes involved in SA biosynthesis, VvEDS1 and VvSARD1, were more highly expressed in Thompson Seedless than in Pinot Noir. Moreover, the content of endogenous SA is at least five‐times higher in Thompson Seedless than in Pinot Noir. Increased trimethylation of H3K27 of VvEDS1 and VvSARD1 may be correlated with lower SA content in Pinot Noir. We also demonstrate that VvHDZ28 positively regulates the expression of VvEDS1. Moreover, over‐expression of VvHDZ28 results in seedless fruit and increased SA contents in Solanum lycopersicum. Our results reveal the potential role of SA and feedback regulation of VvHDZ28 in seedless grapes."

Authors: Dan Zhou, Weifeng Shen, Yuchao Cui, Yuqin Liu, Xijun Zheng, Yan Li, Minliang Wu, Shanru Fang, Chunhong Liu, Ming Tang, Yin Yi, Mingfu Zhao and Liang Chen.

Frontiers in Plant Science (2021)

Abstract: "Panicle degradation causes severe yield reduction in rice. There are two main types of panicle degradation: apical spikelet abortion and basal degeneration. In this study, we isolated and characterized the apical panicle abortion mutant apical spikelet abortion (asa), which exhibits degeneration and defects in the apical spikelets. This mutant had a pleiotropic phenotype, characterized by reduced plant height, increased tiller number, and decreased pollen fertility. Map-based cloning revealed that OsASA encodes a boric acid channel protein that showed the highest expression in the inflorescence, peduncle, and anther. RNA-seq analysis of the asa mutant vs wild-type (WT) plants revealed that biological processes related to reactive oxygen species (ROS) homeostasis and salicylic acid (SA) metabolism were significantly affected. Furthermore, the asa mutants had an increased SA level and H2O2 accumulation in the young panicles compared to the WT plants. Moreover, the SA level and the expression of OsPAL3, OsPAL4, and OsPAL6 genes (related to SA biosynthesis) were significantly increased under boron-deficient conditions in the asa mutant and in OsASA-knockout plants. Collectively, these results suggest that the boron distribution maintained by OsASA is required for normal panicle development in a process that involves modulating ROS homeostasis and SA biosynthesis."