From binding proteins to hormone receptors?

Phytohormones exert in responsive plant cells specific biochemical and physiological effects. It is a widely held view that phytohormones are first recognized by specific receptors which initiate the transduction of the hormonal signal. While hormone receptors are well studied in many eukaryotes ranging from yeast to man, we are lacking a detailed understanding of phytohormone receptors. Phytohormone binding proteins have been suspected to provide candidates for such receptors. In this review recent progress towards molecular analysis of such proteins and their genes will be summarized.     

Structural basis for the regulation of phytohormone receptors

Phytohormones are central players in diverse plant physiological events, such as plant growth, development, and environmental stress and defense responses. The elucidation of their regulatory mechanisms through phytohormone receptors could facilitate the generation of transgenic crops with cultivation advantages and the rational design of growth control chemicals. During the last decade, accumulated structural data on phytohormone receptors have provided critical insights into the molecular mechanisms of phytohormone perception and signal transduction. Here, we review the structural bases of phytohormone recognition and receptor activation. As a common feature, phytohormones regulate the interaction between the receptors and their respective target proteins (also called co-receptors) by two types of regulatory mechanisms, acting as either “molecular glue” or an “allosteric regulator.” However, individual phytohormone receptors adopt specific structural features that are essential for activation. In addition, recent studies have focused on the molecular diversity of redundant phytohormone receptors.     

Modern aspects of studying phytohormones. Cytokinins

The review presents current data on mechanisms of cytokinin action in plants. By analogy with the first part (Ivanova et al., 1999), in which general principles of phytohormone action and cardinal trends of phytohormone investigations were examined, here the relevant information on mechanisms of action of auxins and gibberellins has been given, and taking cytokines as example an attempt has been done to summarize the literature data on the number of questions offered for analysing hormones of high animals (Gudwin, Merser, 1986). The review demonstrates that mechanisms of cytokine action at the cellular level are not known in many cases. One of the most significant factors in the action of phytohormones of this class on plants is their concentration, determined by their synthesis, transportation and further chemical conversions. This paper points to a poor knowledge of the relative role of these processes in regulation of cytokinin contents and their distribution among plant organs. Two possible ways of studying cytokinin action at the present day stage of investigations have been designated: 1) revealing the cytokinin expressed genes and establishing mechanisms of their action; 2) estimation of endogenous cytokinin alteration and the influence of this alteration on definite processes in the cell with the help of ipt-gene from t-DNA of Agrobacterium tumefaciens.     

Biosynthesis of phytohormones in algae

Like in the case of higher plants, algal growth and development are controlled by the hormonal regulatory system. Essentially all known phytohormones were identified in various algal taxa, and the range of their physiological activities was confirmed. At the same time, our knowledge of enzymes involved in the phytohormone synthesis in algae is rather limited. Data concerning genes encoding these enzymes are still more fragmentary. Current data about proteomes of some algae allow the revealing of amino acid sequences with homology to those of the higher plant enzymes and their conserved domains.     

The involvement of phytohormones in the plant sex regulation

The data concerning the plant sex regulation by phytohormones are presented. Functioning of signaling pathways regulating floral development and sex expression, including those with phytohormone involvement, are considered. The role of phytohormones in the functioning of systems and mechanisms of sex regulation is analyzed. The examples of sex reversion by plant treatment with phytohormones are presented. It is demonstrated that many genes determining sex encode proteins involved in the phytohormone metabolism. The significance of phytohormone investigation for the understanding of molecular mechanisms of plant sex regulation is discussed.     

植物荫蔽胁迫的激素信号响应

植物的生长发育与光信号密切相关, 外界光强、光质的变化会改变植物的生长发育状态。在自然或人工生态系统中, 植株个体的光环境往往会被其周围植物所影响, 导致荫蔽胁迫, 其主要表现为光合有效辐射以及红光与远红光比值(R:FR)降低。荫蔽胁迫对植物生长发育的多个时期均有影响, 如抑制种子萌发、促进幼苗下胚轴伸长及促进植物花期提前等, 这对农业生产不利, 会导致作物产量以及品质的降低。植物激素是调控植物生长发育的关键内源因子。大量研究表明, 生长素(IAA)、赤霉素(GA)及油菜素甾醇(BR)等植物激素均参与介导植物的荫蔽胁迫响应。当植物处于荫蔽胁迫时, 光信号的改变会影响植物激素的合成及信号转导。不同植物激素对荫蔽胁迫的响应各不相同, 但其信号通路之间却存在互作关系, 从而形成复杂的网络状调控路径。该文总结了几种主要植物激素(生长素、赤霉素、油菜素甾醇及乙烯)响应荫蔽胁迫的机理, 重点论述了荫蔽胁迫对植物激素合成及信号通路的影响, 以及植物激素调控荫蔽胁迫下植物生长的分子机理, 并对未来潜在的研究热点进行了分析。     

Interplay of phytohormones and epigenetic regulation: A recipe for plant development and plasticity

Both phytohormone signaling and epigenetic mechanisms have long been known to play crucial roles in plant development and plasticity in response to ambient stimuli.Indeed,diverse signaling pathways mediated by phytohormones and epigenetic processes integrate multiple upstream signals to regulate various plant traits.Emerging evidence indicates that phytohormones and epigenetic processes interact at multiple levels.In this review,we summarize the current knowledge of the interplay between phytoho...     

生长素调控种子的休眠与萌发

植物种子的休眠与萌发,是植物生长发育过程中的关键阶段,也是生命科学领域的研究热点。种子从休眠向萌发的转换是极为复杂的生物学过程,由外界环境因子、体内激素含量及信号传导和若干关键基因协同调控。大量研究表明,植物激素脱落酸(Abscisic acid, ABA)和赤霉素(Gibberellin acid, GA)是调控种子休眠水平,决定种子从休眠转向萌发的主要内源因子。ABA与GA在含量和信号传导两个层次上的精确平衡,确保了植物种子能以休眠状态在逆境中存活,并在适宜的时间启动萌发程序。生长素(Auxin)是经典植物激素之一,其对向性生长和组织分化等生物学过程的调控已有大量研究。但最近有研究证实,生长素对种子休眠有正向调控作用,这表明生长素是继ABA之后的第二个促进种子休眠的植物激素。本文在回顾生长素的发现历程、阐释生长素体内合成途径及信号传导通路的基础上,重点综述了生长素通过与ABA的协同作用调控种子休眠的分子机制,并对未来的研究热点进行了讨论和展望。     

Jasmonates in arbuscular mycorrhizal interactions

The mutualistic interaction between plants and arbuscular mycorrhizal (AM) fungi is believed to be regulated from the plant side among other signals by the action of phytohormones. Evidences for this are based mainly on application experiments and determination of phytohormone levels in AM roots by comparison to non-mycorrhizal roots. In case of jasmonates, additional proof is given by reverse genetic approaches, which led to first insights into their putative role in the establishment and functioning of the symbiosis. This review summarizes the current data about phytohormone action in AM roots and the role of jasmonates in particular.     

On plant growth regulators and their metabolites: a changing perspective

From seed germination to vegetative growth and flowering virtually all aspects of plant growth and development are influenced by structurally relatively simple substances, termed phytohormones. It has ben argued that the wide range of responses elicited by these substances requires a mode of action that is radically different from those of animal hormones. In contrast to animal hormones, it is often very difficult to distinguish between the site of synthesis and the site of action of phytohormones. Hence, plants may have developed their own mechanisms for synthesis, sequestration and release of active hormones. Current evidence indicates that enzymes that can synthesize and modify phytohormones and their antagonists or hydrolyze phytohormone conjugates to release active hormones which play a role in initiating important regulatory pathways. They are also likely to provide invaluable tools for studying the mechanisms underlying growth and development in plants.     

Integrating hormones into the floral-transition pathway of Arabidopsis thaliana

The transition from vegetative to reproductive growth is a major phase change in angiosperms. In annual plants such as Arabidopsis thaliana (Arabidopsis), this change is irreversible, and as such, the regulation of its timing must be tightly controlled. Plant hormone (phytohormone) signalling is known to regulate suites of morphogenic processes in Arabidopsis a role in flowering-time control is starting to emerge as one key-controlling step. This review focuses on experimental evidence in the Arabidopsis that both classical and newly described phytohormones serve within the signal network leading to a reproductive phase transition, as both positive and repressive elements, depending on the phytohormone and growth conditions. Examples of genetic and pharmacological experiments that implicate phytohormones as components of the floral-timing syndrome will be described. I hope that this review will serve as a primer for future research on the mechanisms of action for each respective phytohormone on the floral transition in Arabidopsis, and lead to further experimentation on the crosstalk that likely bridges between them.     

NOR Activity in Wheat Species with Different Ploidy Levels Treated with Phytohormones

The effects of the phytohormones 6-benzylaminopurine (BAP) and 24-epibrassinolide (EB) on the sizes of nucleoli in the interphase nuclei of root meristem were studied using the silver-staining procedure in wheat species with different ploidy levels (a polyploid series). In addition, the effects of the phytohormones on the cell mitotic activity in the roots of 5-day-old seedlings were studied. The higher the wheat species ploidy level, the higher its sensitivities to BAP and EB were. In diploid wheat, the maximum increase in the nucleolar organizing region (NOR) activity was observed after treatment with considerably higher phytohormone concentrations compared to tetra- and hexaploid wheat species. The phytohormone treatment increased both the sizes and the number of nucleoli in meristematic cells of seedling roots in all wheat species studied. It was assumed that the differences between the responses of wheat species with three different ploidy levels to different concentrations of phytohormones were related to their effects on the methylation/demethylation of cytosine residues in the rDNA promoter region.     

Comprehensive transcriptome analysis of phytohormone biosynthesis and signaling genes in microspore/pollen and tapetum of rice

To investigate the involvement of phytohormones during rice microspore/pollen (MS/POL) development, endogenous levels of IAA, gibberellins (GAs), cytokinins (CKs) and abscisic acid (ABA) in the mature anther were analyzed. We also analyzed the global expression profiles of genes related to seven phytohormones, namely auxin, GAs, CKs, brassinosteroids, ethylene, ABA and jasmonic acids, in MS/POL and tapetum (TAP) using a 44K microarray combined with a laser microdissection technique (LM-array analysis). IAA and GA(4) accumulated in a much higher amount in the mature anther compared with the other tissues, while CKs and ABA did not. LM-array analysis revealed that sets of genes required for IAA and GA synthesis were coordinately expressed during the later stages of MS/POL development, suggesting that these genes are responsible for the massive accumulation of IAA and GA(4) in the mature anther. In contrast, genes for GA signaling were preferentially expressed during the early developmental stages of MS/POL and throughout TAP development, while their expression was down-regulated at the later stages of MS/POL development. In the case of auxin signaling genes, such mirror-imaged expression observed in GA synthesis and signaling genes was not observed. IAA receptor genes were mostly expressed during the late stages of MS/POL development, and various sets of AUX/IAA and ARF genes were expressed during the different stages of MS/POL or TAP development. Such cell type-specific expression profiles of phytohormone biosynthesis and signaling genes demonstrate the validity and importance of analyzing the expression of phytohormone-related genes in individual cell types independently of other cells/tissues.     

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.     

Mass spectrometric exploration of phytohormone profiles and signaling networks

Phytohormones have crucial roles in plant growth, development, and acclimation to environmental stress; however, measuring phytohormone levels and unraveling their complex signaling networks and interactions remains challenging. Mass spectrometry (MS) has revolutionized the study of complex biological systems, enabling the comprehensive identification and quantification of phytohormones and their related targets. Here, we review recent advances in MS technologies and highlight studies that have used MS to discover and analyze phytohormone-mediated molecular events. In particular, we focus on the application of MS for profiling phytohormones, elucidating phosphorylation signaling, and mapping protein interactions in plants.     

NOR (nucleolar organizer region) activity in wheat species with different ploidy levels treated with phytohormones

The effects of the phytohormones 6-benzylaminopurine (BAP) and 24-epibrassinolide (EB) on the nucleolar sizes in the interphase nuclei of root meristem were studied using the silver-staining procedure in wheat species with different ploidy levels (a polyploid series). In addition, the effects of the phytohormones on the cell mitotic activity in the roots of 5-day-old seedlings were studied. The higher the wheat species ploidy level, the higher its sensitivities to BAP and EB were. In diploid wheat, the maximum increase in the nucleolar organizing region (NOR) activity was observed after treatment with considerably higher phytohormone concentrations compared to tetra- and hexaploid wheat species. The phytohormone treatment increased both the sizes and the number of nucleoli in meristematic cells of seedling roots in all wheat species studied. It was assumed that the differences between the responses of wheat species with three different ploidy levels to different concentrations of phytohormones were related to their effects on the methylation/demethylation of cytosine residues in the rDNA promoter region.