Current understanding of the interplays between host hormones and plant viral infections

Phytohormones mediate plant development and responses to stresses caused by biotic agents or abiotic factors. The functions of phytohormones in responses to viral infection have been intensively studied, and the emerging picture of complex mechanisms provides insights into the roles that phytohormones play in defense regulation as a whole. These hormone signaling pathways are not simple linear or isolated cascades, but exhibit crosstalk with each other. Here, we summarized the current understanding of recent advances for the classical defense hormones salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) and also the roles of abscisic acid (ABA), auxin, gibberellic acid (GA), cytokinins (CKs), and brassinosteroids (BRs) in modulating plant–virus interactions.     

Effects of phytohormones on the cytoskeleton of the plant cell

This review highlights the effects of ??classic?? phytohormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene, and brassinosteroids) and also of important signaling molecules, such as jasmonic acid, strigolactones, and nitric oxide, on the main components of the plant cytoskeleton, microtubules and microfilaments. The effects of these growth regulators on orientation and organization of microtubules and actin filaments, realization of cytoskeleton-dependent processes, expression of tubulin and actin genes, and interaction of various phytohormones in their influence on the cytoskeleton are discussed.     

植物激素糖基化修饰研究进展

植物激素对植物的生长发育有重要的调节作用。由于激素的作用依赖于其浓度, 所以植物内源活性激素的水平必须受到严格控制, 而糖基化修饰被认为是调控激素活性水平的重要方式之一。随着植物激素糖基化修饰相关糖基转移酶基因不断被克隆与鉴定, 多种植物激素的糖基化修饰机制和功能作用逐渐被揭示。该文重点介绍了近年来植物生长素、细胞分裂素、脱落酸、油菜素内酯、水杨酸、茉莉酸等植物激素的糖基转移酶活性鉴定与功能研究进展。同时, 对植物激素糖基化修饰领域存在的问题和发展前景进行了讨论。     

Histones and Plant Hormones: New Evidence for an Interesting Interplay

As any living organism, plants have to respond to a wide variety of biotic and abiotic signals. One of the most important challenges for the plant cell is the response to plant hormones, compounds that regulate almost all aspects of plant development. This process involves the appropriate alteration of chromatin structure and function which can be facilitated by a number of different mechanisms, including histone covalent modifications, incorporation of distinct histone variants, chromatin remodeling and epigenetic regulation of gene expression. On the other hand, distinct chromatin states may in turn influence plant hormone biosynthesis and signaling. This article aims to review the evidence accumulated the last years concerning the effect of the major plant hormones - auxin, gibberellins, cytokinins, ethylene, abscisic acid, brassinosteroids and jasmonic acid - signaling on histone variants and modification pattern and to discuss the interplay between histones and hormones at plant chromatin.     

Role of Phytohormones in Regulating Heat Stress Acclimation in Agricultural Crops

Heat stress (HS) seriously affects crop growth, causing significant crop yield losses worldwide. The regulatory mechanisms controlling HS tolerance in plants are not well understood. Phytohormones are important molecules for coordinating myriad of phenomena related to plant growth and development. They are also essential endogenous signaling molecules that actively mediate numerous physiological responses under abiotic stress by triggering stress-responsive regulatory genes involved in plant growth. This review updates the central role of various phytohormones—indole acetic acid, gibberellic acid, abscisic acid, cytokinins, ethylene, salicylic acid, brassinosteroids, strigolactone, and jasmonic acid—in regulating the HS response so that plants can adapt to increasing temperature stress. We also reveal how these stress-responsive phytohormones switch on various regulatory gene(s) and genes encoding antioxidants and heat shock proteins (HSPs) to combat HS in various plant species.

     

Role of phytohormones in insect-specific plant reactions

The capacity to perceive and respond is integral to biological immune systems, but to what extent can plants specifically recognize and respond to insects? Recent findings suggest that plants possess surveillance systems that are able to detect general patterns of cellular damage as well as highly specific herbivore-associated cues. The jasmonate (JA) pathway has emerged as the major signaling cassette that integrates information perceived at the plant-insect interface into broad-spectrum defense responses. Specificity can be achieved via JA-independent processes and spatio-temporal changes of JA-modulating hormones, including ethylene (ET), salicylic acid (SA), abscisic acid (ABA), auxin, cytokinins (CK), brassinosteroids (BR) and gibberellins (GB). The identification of receptors and ligands and an integrative view of hormone-mediated response systems are crucial to understand specificity in plant immunity to herbivores.     

Auxin: a master regulator in plant root development

The demand for increased crop productivity and the predicted challenges related to plant survival under adverse environmental conditions have renewed the interest in research in root biology. Various physiological and genetic studies have provided ample evidence in support of the role of plant growth regulators in root development. The biosynthesis and transport of auxin and its signaling play a crucial role in controlling root growth and development. The univocal role of auxin in root development has established it as a master regulator. Other plant hormones, such as cytokinins, brassinosteroids, ethylene, abscisic acid, gibberellins, jasmonic acid, polyamines and strigolactones interact either synergistically or antagonistically with auxin to trigger cascades of events leading to root morphogenesis and development. In recent years, the availability of biological resources, development of modern tools and experimental approaches have led to the advancement of knowledge in root development. Research in the areas of hormone signal perception, understanding network of events involved in hormone action and the transport of plant hormones has added a new dimension to root biology. The present review highlights some of the important conceptual developments in the interplay of auxin and other plant hormones and associated downstream events affecting root development.     

Signs of change: hormone receptors that regulate plant development

Hormonal signalling plays a pivotal role in almost every aspect of plant development, and of high priority has been to identify the receptors that perceive these hormones. In the past seven months, the receptors for the plant hormones auxin, gibberellins and abscisic acid have been identified. These join the receptors that have previously been identified for ethylene, brassinosteroids and cytokinins. This review therefore comes at an exciting time for plant developmental biology, as the new findings shed light on our current understanding of the structure and function of the various hormone receptors, their related signalling pathways and their role in regulating plant development.     

Complex phytohormone responses during the cold acclimation of two wheat cultivars differing in cold tolerance, winter Samanta and spring Sandra

Hormonal changes accompanying the cold stress (4°C) response that are related to the level of frost tolerance (FT; measured as LT50) and the content of the most abundant dehydrin, WCS120, were compared in the leaves and crowns of the winter wheat (Triticum aestivum L.) cv. Samanta and the spring wheat cv. Sandra. The characteristic feature of the alarm phase (1 day) response was a rapid elevation of abscisic acid (ABA) and an increase of protective proteins (dehydrin WCS120). This response was faster and stronger in winter wheat, where it coincided with the downregulation of bioactive cytokinins and auxin as well as enhanced deactivation of gibberellins, indicating rapid suppression of growth. Next, the ethylene precursor aminocyclopropane carboxylic acid was quickly upregulated. After 3-7 days of cold exposure, plant adaptation to the low temperature was correlated with a decrease in ABA and elevation of growth-promoting hormones (cytokinins, auxin and gibberellins). The content of other stress hormones, i.e., salicylic acid and jasmonic acid, also began to increase. After prolonged cold exposure (21 days), a resistance phase occurred. The winter cultivar exhibited substantially enhanced FT, which was associated with a decline in bioactive cytokinins and auxin. The inability of the spring cultivar to further increase its FT was correlated with maintenance of a relatively higher cytokinin and auxin content, which was achieved during the acclimation period.     

Conjugates of abscisic acid, brassinosteroids, ethylene, gibberellins, and jasmonates

Phytohormones, including auxins, abscisic acid, brassinosteroids, cytokinins, ethylene, gibberellins, and jasmonates, are involved in all aspects of plant growth, and developmental processes as well as environmental responses. However, our understanding of hormonal homeostasis is far from complete. Phytohormone conjugation is considered as a part of the mechanism to control cellular levels of these compounds. Active phytohormones are changed into multiple forms by acylation, esterification or glycosylation, for example. It seems that conjugated compounds could serve as pool of inactive phytohormones that can be converted to active forms by de-conjugation reactions. Some conjugates are thought to be temporary storage forms, from which free active hormones can be released after hydrolysis. It is also believed that conjugation serves functions, such as irreversible inactivation, transport, compartmentalization, and protection against degradation. The nature of abscisic acid, brassinosteroid, ethylene, gibberellin, and jasmonate conjugates is discussed.     

Mechanisms of brassinosteroids interacting with multiple hormones

Various environmental and internal cues play essential roles in regulating diverse aspects of plant growth and development. Phytohormones usually coordinate multiple stimuli to directly regulate multiple developmental programs. Recent studies have provided progresses into the complexity of their cross talk. Particularly, the signaling pathways of various phytohormones have been revealed, leading to the discovery of the mechanisms of the interplay among different hormone signaling pathways. This review focuses on the recent advances of the signaling cross-talk between brassinosteroids and other hormones, including abscisic acid, auxin, gibberellins, ethylene and jasmonate.Key words: brassinosteroids, plant hormone, abscisic acid, auxin, cross talk, signaling     

Biosynthesis and beneficial effects of microbial gibberellins on crops for sustainable agriculture

Soil microbes promote plant growth through several mechanisms such as secretion of chemical compounds including plant growth hormones. Among the phytohormones, auxins, ethylene, cytokinins, abscisic acid and gibberellins are the best understood compounds. Gibberellins were first isolated in 1935 from the fungus Gibberella fujikuroi and are synthesized by several soil microbes. The effect of gibberellins on plant growth and development has been studied, as has the biosynthesis pathways, enzymes, genes and their regulation. This review revisits the history of gibberellin research highlighting microbial gibberellins and their effects on plant health with an emphasis on the early discoveries and current advances that can find vital applications in agricultural practices.     

Phytohormones and microRNAs as sensors and regulators of leaf senescence: Assigning macro roles to small molecules

Ageing or senescence is an intricate and highly synchronized developmental phase in the life of plant parts including leaf. Senescence not only means death of a plant part, but during this process, different macromolecules undergo degradation and the resulting components are transported to other parts of the plant. During the period from when a leaf is young and green to the stage when it senesces, a multitude of factors such as hormones, environmental factors and senescence associated genes (SAGs) are involved. Plant hormones including salicylic acid, abscisic acid, jasmonic acid and ethylene advance leaf senescence, whereas others like cytokinins, gibberellins, and auxins delay this process. The environmental factors which generally affect plant development and growth, can hasten senescence, the examples being nutrient dearth, water stress, pathogen attack, radiations, high temperature and light intensity, waterlogging, and air, water or soil contamination. Other important influences include carbohydrate accumulation and high carbon/nitrogen level. To date, although several genes involved in this complex process have been identified, still not much information exists in the literature on the signalling mechanism of leaf senescence. Now, the Arabidopsis mutants have paved our way and opened new vistas to elucidate the signalling mechanism of leaf senescence for which various mutants are being utilized. Recent studies demonstrating the role of microRNAs in leaf senescence have reinforced our knowledge of this intricate process. This review provides a comprehensive and critical analysis of the information gained particularly on the roles of several plant growth regulators and microRNAs in regulation of leaf senescence.     

The role of hormonal balance in plant adaptation to flooding

The effect of flooding on the growth parameters and hormonal dynamics (anxins, abscisic acid, cytokinins, gibberellins, and ethylene) has been studied in a vegetation experiment on the leaves of wheat (Triticum aestivum L.) and oat (Avena sativa L.). Growth inhibition during flooding in both species was due to the accumulation of abscisic acid and ethylene, while the repair processes were due to the increased level of auxins, cytokinins, and gibberellins. The difference in the hormonal response in wheat and oat to flooding, in particular, the degree and timing of accumulation of abscisic and indoleacetic acids and different dynamics of the level of cytokinins and gibberellins, induced their different physiological response, which determined the level of their resistance. The growth control of cereals during flooding as well as the hormonal dynamics are proposed to rely on the strategy of plant ontogenetic adaptation.     

The Physiological,Biochemical and Molecular Roles of Brassinosteroids and Salicylic Acid in Plant Processes and Salt Tolerance

Plant hormones regulate plant growth and development by affecting an array of cellular, physiological, and developmental processes, including, but not limited to, cell division and elongation, stomatal regulation, photosynthesis, transpiration, ion uptake and transport, initiation of leaf, flower and fruit development, and senescence. Environmental factors such as salinity, drought, and extreme temperatures may cause a reduction in plant growth and productivity by altering the endogenous levels of plant hormones, sensitivity to plant hormones, and/or signaling pathways. Molecular and physiological studies have determined that plant hormones and abiotic stresses have interactive effects on a number of basic biochemical and physiological processes, leading to reduced plant growth and development. Various strategies have been considered or employed to maximize plant growth and productivity under environmental stresses such as salt-stress. A fundamental approach is to develop salt-tolerant plants through genetic means. Breeding for salt tolerance, however, is a long-term endeavor with its own complexities and inherent difficulties. The success of this approach depends, among others, on the availability of genetic sources of tolerance and reliable screening techniques, identification and successful transfer of genetic components of tolerance to desired genetic backgrounds, and development of elite breeding lines and cultivars with salt tolerance and other desirable agricultural characteristics. Such extensive processes have delayed development of successful salt-tolerant cultivars in most crop species. An alternative and technically simpler approach is to induce salt tolerance through exogenous application of certain plant growth–regulating compounds. This approach has gained significant interest during the past decade, when a wealth of new knowledge has become available on the beneficial roles of the six classes of plant hormones (auxins, gibberellins, cytokinins, abscisic acid, ethylene, and brassinosteroids) as well as several other plant growth–regulating substances (jasmonates, salicylates, polyamines, triacontanol, ascorbic acid, and tocopherols) on plant stress tolerance. Among these, brassinosteroids (BRs) and salicylic acid (SA) have been studied most extensively. Both BRs and SA are ubiquitous in the plant kingdom, affecting plant growth and development in many different ways, and are known to improve plant stress tolerance. In this article, we review and discuss the current knowledge and possible applications of BRs and SA that could be used to mitigate the harmful effects of salt-stress in plants. We also discuss the roles of exogenous applications of BRs and SA in the regulation of various biochemical and physiological processes leading to improved salt tolerance in plants.     

Signaling Interactions During Nodule Development

Nitrogen fixing bacteria, collectively referred to as rhizobia, are able to trigger the organogenesis of a new organ on legumes, the nodule. The morphogenetic trigger is a Rhizobium-produced lipochitin-oligosaccharide called the Nod factor, which is necessary, and in some legumes sufficient, for triggering nodule development in the absence of the bacterium. Because plant development is substantially influenced by plant hormones, it has been hypothesized that plant hormones (mainly the classical hormones abscisic acid, auxin, cytokinins, ethylene and gibberellic acid) regulate nodule development. In recent years, evidence has shown that Nod factors might act in legumes by changing the internal plant hormone balance, thereby orchestrating the nodule developmental program. In addition, many nonclassical hormonal signals have been found to play a role in nodule development, some of them similar to signals involved in animal development. These compounds include peptide hormones, nitric oxide, reactive oxygen species, jasmonic acid, salicylic acid, uridine, flavonoids and Nod factors themselves. Environmental factors, in particular nitrate, also influence nodule development by affecting the plant hormone status. This review summarizes recent findings on the involvement of classical and nonclassical signals during nodule development with the aim of illustrating the multiple interactions existing between these compounds that have made this area so complicated to analyze.     

Plant hormones and plant growth regulators in plant tissue culture

Summary This is a short review of the classical and new, natural and synthetic plant hormones and growth regulators (phytohormones) and highlights some of their uses in plant tissue culture. Plant hormones rarely act alone, and for most processes— at least those that are observed at the organ level—many of these regulators have interacted in order to produce the final effect. The following substances are discussed: (a) Classical plant hormones (auxins, cytokinins, gibberellins, abscisic acid, ethylene and growth regulatory substances with similar biological effects. New, naturally occurring substances in these categories are still being discovered. At the same time, novel structurally related compounds are constantly being synthesized. There are also many new but chemically unrelated compounds with similar hormone-like activity being produced. A better knowledge of the uptake, transport, metabolism, and mode of action of phytohormones and the appearance of chemicals that inhibit synthesis, transport, and action of the native plant hormones has increased our knowledge of the role of these hormones in growth and development. (b) More recently discovered natural growth substances that have phytohormonal-like regulatory roles (polyamines, oligosaccharins, salicylates, jasmonates, sterols, brassinosteroids, dehydrodiconiferyl alcohol glucosides, turgorins, systemin, unrelated natural stimulators and inhibitors), as well as myoinositol. Many of these growth active substances have not yet been examined in relation to growth and organized developmentin vitro.     

Plant hormone interactions: how complex are they?

Models describing plant hormone interactions are often complex and web-like. Here we assess several suggested interactions within one experimental system, elongating pea internodes. Results from this system indicate that at least some suggested interactions between auxin, gibberellins (GAs), brassinosteroids (BRs), abscisic acid (ABA) and ethylene do not occur in this system or occur in the reverse direction to that suggested. Furthermore, some of the interactions are relatively weak and may be of little physiological relevance. This is especially true if plant hormones are assumed to show a log-linear response curve as many empirical results suggest. Although there is strong evidence to support some interactions between hormones (e.g. auxin stimulating ethylene and bioactive GA levels), at least some of the web-like complexities do not appear to be justified or are overstated. Simpler and more targeted models may be developed by dissecting out key interactions with major physiological effects.     

A comparative genomic analysis of plant hormone related genes in different species

Plant hormones are small molecules that play important roles throughout the life span of a plant,known as auxin,gibberellin,cyto-kinin,abscisic acid,ethylene,jasmonic acid,salicylic acid,and brassinosteroid.Genetic and molecular studies in the model organism Arabidopsis thaliana have revealed the individual pathways of various plant hormone responses.In this study,we selected 479 genes that were convincingly associated with various hormone actions based on genetic evidence.By using these 479 genes as querie...     

Simultaneous quantification of major phytohormones and related compounds in crude plant extracts by liquid chromatography-electrospray tandem mass spectrometry

A rapid and sensitive method was developed for simultaneous quantification of multiple classes of phytohormones and some related metabolites in crude plant extracts without purification or derivatization. High-performance liquid chromatography and electrospray ionization–tandem mass spectrometry with multiple reaction monitoring were used to quantify auxins, cytokinins, abscisic acid, gibberellins, jasmonates, salicylates, and a number of related metabolites in crude plant extracts. The technology was applied to analyze biotic and abiotic stress-induced changes of phytohormones in Arabidopsis tissues, starting with 50–100 mg fresh tissue. Biotic and/or abiotic stresses were shown to differentially affect levels of salicylic acid, jasmonic acid, indole-3-acetic acid, and benzoic acid, in comparison to their methyl esters. Compared with previous methods, sample preparation time and amount of sample required for analysis of phytohormones are reduced, and more classes of hormones are quantitatively profiled. Structurally diverse compounds from complicated biological matrices are determined with high selectivity and sensitivity.