光色素信号通路中磷酸化修饰研究进展

光是植物的唯一能量来源, 植物在进化过程中产生不同的光敏色素来感知光信号。光信号通路中元件通常被特异翻译后修饰调节。光敏色素是一种自磷酸化的丝氨酸/苏氨酸蛋白激酶, 可以被一些蛋白磷酸酶去磷酸化。通过对光敏色素A (phyA)和光敏色素B (phyB)的自磷酸化位点研究, 发现自磷酸化对光敏色素的功能及其介导的信号通路起着非常重要的作用。光激活的光敏色素诱导光敏色素作用因子(PIF)磷酸化, 这对于PIF的正常降解及光形态建成的起始是必需的。该文主要介绍了光敏色素信号通路磷酸化修饰的最新进展, 以期为深入研究光敏色素信号转导机制提供参考。     

光敏色素信号通路中磷酸化修饰研究进展

光是植物的唯一能量来源,植物在进化过程中产生不同的光敏色素来感知光信号。光信号通路中元件通常被特异翻译后修饰调节。光敏色素是一种自磷酸化的丝氨酸/苏氨酸蛋白激酶,可以被一些蛋白磷酸酶去磷酸化。通过对光敏色素A(phy A)和光敏色素B(phy B)的自磷酸化位点研究,发现自磷酸化对光敏色素的功能及其介导的信号通路起着非常重要的作用。光激活的光敏色素诱导光敏色素作用因子(PIF)磷酸化,这对于PIF的正常降解及光形态建成的起始是必需的。该文主要介绍了光敏色素信号通路磷酸化修饰的最新进展,以期为深入研究光敏色素信号转导机制提供参考。     

光敏色素分子及其信号转导途径

作为植物体内的一种光受体,光敏色素在植物的光形态建成过程中意义重大。植物光敏色素及由它介导的信号传导途径是目前细胞生物学、发育生物学和分子生物学研究的热点之一。本文介绍了光敏色素的分子特性、生理功能和信号转导途径等方面的研究进展。     

光敏色素光转化生理学特性研究进展(英文)

植物主要光受体光敏色素调节植物的多种光调控,使其作出最适宜的光生长,如:光形态建成.光敏色素接受光信号的生物功能基于其红光吸收型(Pr)和具有生理活性的远红光吸收型(Pfr)之间的光可逆式光转化.依据光生物学的标准该转化过程与光合作用相比是一个低能光反应过程,而且其间产生的中间过渡态和光敏色素的亚库可能反过来影响光转化的过程而最终表现出生理功能.在此,主要综述了近年来运用时间分辨动力学特别是差分荧光和光化学,研究光敏色素及其中间过度态光生物物理和光生物化学特性的若干进展,讨论了光信号转导的原初光反应的机理.     

光敏色素信号传导研究的一项重要结果

光敏色素（phytochrome）控制高等植物的许多分子、细胞及发育反应。尽管对光敏色素分子本身的认识已很深入，然而，其信号传导过程一直是植物发育生物学中悬而未决的问题。不久前，用单细胞测定法鉴定了参与光敏色素信号传导的几种中间体。本文就此进展简要综述。     

光敏色素与光调控

生物体的新陈代谢和生长发育主要受遗传信息及环境信息的调控,遗传信息规定了个体发育的潜在模式,但它的实现在很大程度上受控于环境信息。光作为主要的环境因子,不仅提供光合作用所需的能量,而且触发植物形态变化、质体分化、新陈代谢等重要反应(统称为光形态建成)。光形态建成至少与四个不同类型光受体相关:光敏色素、蓝光受体、UV-A受体、UV-B受体,其中研究最深入的当属光敏色素。自1983年Vierstra和Quail分离到完整的光敏色素蛋白质以来,科学家相继对光敏色素的分子种类、生物合成与调控及生理机制展开了广泛深入的研究,并且取得了令人瞩目的进展。时至今日,随着新方法、新技术的应用,从光敏色素感受光刺激到基因在细胞核中表达,再到光形态建成的整个信号传递途径已逐步为人们所认识,许多与光敏色素调节有关的顺式因子及相应的DNA结合蛋白也已被确定。功能研究发现,没有哪一个反式作用因子在光调节的表达中单独起作用,可见光敏色素调控的基因表达是相当复杂的。本文拟就光敏色素分子、光敏色素基因家族、光敏色素所激活的信号传递途径及光敏色素与基因表达的关系等方面做一综述。     

植物的光受体及其调控机制的研究

近年来,通过对植物的分子遗传学研究,在植物光受体及其在光形态建成中对植物生长发育的调控机制方面取得了显著进展。从光受体及基因家族的概况,包括光敏色素、隐花色素、向光素的基本结构、分子特征、基因和信号转导等,介绍了光受体在光控发育调节机制方面的研究进展情况。     

植物中的光敏色素

光敏色素是植物体内的光受体。本介绍了光敏色素的结构、特征及由光敏色素引发的昼夜节律生物钟,着重介绍了在信号转导和昼夜节律系统中的光敏色素作用因子。     

光对种子萌发的影响机理研究进展

种子萌发是植物成功实现天然更新的关键环节, 需要适宜的温度、水分或光照条件。对于需光性种子, 光照是决定其萌发与否或萌发率高低的主要因素。光对植物种子萌发的影响不仅是一个复杂的生理过程, 也是受到调控的信号传递和基因表达过程。该文系统总结了影响种子萌发的光照属性、光与水/热耦合作用和种子的光属性(光敏色素)与种子萌发的关系, 明确了光调控种子萌发的生态意义; 重点综述了种子内光敏色素调控种子萌发的生理反应模式和光敏色素的光信号转导途径。试图为全面评估光对种子萌发的影响和将来开展更深入的研究提供参考。     

蓝细菌光敏色素的分子结构、生物合成和可逆光致变色效应

蓝细菌光敏色素(CBCRs)是蓝细菌中感受光的重要光受体,能够响应从紫外光到红外光范围内的光信号,进而影响蓝细菌的光化学行为。蓝细菌光敏色素通过N-末端GAF(cGMP phosphodiesterase,adenylyl cyclase and FhlA domain)结构域中保守性半胱氨酸共价结合藻胆色素,形成具有感光生理功能的色素蛋白质。本文重点在分子水平上综述了蓝细菌光敏色素的分子结构、生物合成和可逆光致变色效应机理,并基于最新的研究进展,就蓝细菌光敏色素今后的研究方向进行了展望。     

Interactions between native oat phytochrome and tetrapyrroles

The suggestion, that the increase in the far-UV CD signal of the 124 kDa oat phytochrome upon phototransformation of the Pr to Pfr form is possibly due to the chromophore interaction with the N-terminus segment of the phytochrome protein in the Pfr from (Chai, Y.G., Song, P.S., Cordonnier, M.-M. and Pratt, L.H. (1987) Biochemistry 26, 4947-4952), has been investigated by measuring the circular dichroism in the absence of exogenous tetrapyrrolic chromophores (bilirubin, biliverdin, chlorophyllin and hemin). Open tetrapyrrolic chromophores (bilirubin and biliverdin) did not have any significant effect on the phototransformability of the far-UV CD signal of the phytochrome, whereas closed tetrapyrroles (chlorophyllin and hemin) almost completely blocked the increase in the far-UV CD signal upon Pr to Pfr phototransformation. However, closed tetrapyrroles had no effect on the decrease in the CD signal upon Pfr to Pr photoconversion. Secondary structure analysis showed that the alpha-helix content of both Pr and Pfr forms of phytochrome (with 53 and 56% alpha-helical content, respectively) increased to 62% when a 50-fold molar excess of chlorophyllin was added to them separately. Spectral phototransformation of phytochrome was not affected in the presence of tetrapyrroles, except in the case of hemin. A 50-fold molar mass of hemin caused a significant bleaching of the Pfr form of phytochrome but not that of the Pr form. These results suggest that the chromophore-protein interaction is significantly altered during the phototransformation of phytochrome.     

In vivo phytochrome reversion in immature tissue of the alaska pea seedling

Reversion of far red-absorbing phytochrome to red-absorbing phytochrome without phytochrome destruction (that is, without loss of absorbancy and photoreversibility) occurs in the following tissues of etiolated Alaska pea seedlings (Pisum sativum L.): young radicles (24 hours after start of imbibition), young epicotyls (48 hours after start of imbibition), and the juvenile region of the epicotyl immediately subjacent to the plumule in older epicotyls. Reversion occurs rapidly in the dark during the first 30 minutes following initial phototransformation of red-absorbing phytochrome to far red-absorbing phytochrome. If these tissues are illuminated continuously with red light for 30 minutes, the total amount of phytochrome remains unchanged. Beyond 30 minutes after a single phototransformation or after the start of continuous red irradiation, phytochrome destruction commences. In young radicles, sodium azide inhibits this destruction, but does not affect reversion. In older tissues in which far red-absorbing phytochrome destruction begins immediately upon phototransformation, strong evidence for simultaneous far red-absorbing phytochrome reversion is obtained from comparison of far red-absorbing phytochrome loss in the dark following a single phototransformation with far red-absorbing phytochrome loss under continuous red light.     

Phototransformation of oat phytochrome with millisecond and submillisecond flashes: The level of the photostationary Pfr/Ptot ratio is modified by photoreversible intermediates

Photoconversion of the red-absorbing form of phytochrome (P_r) to the far-red-absorbing form of phytochrome (P_fr) and vice versa has been measured spectrophotometrically at 10°C in immobilized and soluble phytochrome (118 kdalton), prepared from 5-day-old etiolated oat seedlings ( Avena saliva L. cv. Sol II). The photostationary equilibrium φ= P_frP_tot (with P_tot= total amount of phytochrome P_r+ P_fr) for red light depends on whether it is established by repetitive pulses (≥ 5 s) or by repetitive flashes (≥ 4 ms). In the wavelength region around 660 nm, a lower φ is reached with flashes as compared to that with pulses. This difference becomes negligible if the wavelength is shortened to the 600 nm region, and it also disappears if the fluence of each individual flash is reduced. In contrast, in long-wavelength red light and short-wavelength far-red light, a higher φ is reached with flashes than with pulses.
We relate the differences in φ for flash and pulse irradiation to photochromic systems between P_r and photoreversible intermediates in the phototransformation pathway P_r→ P_fr. Thus, light absorption by phytochrome intermediates can be limiting for the quantitative relationship between light signal and P_fr formed.     

Circular dichroism of phytochrome intermediates

Phototransformation P_t to P_fr was investigated with 124-kDa phytochrome from etiolated oat seedlings ( Avena sativa L. cv. Pirol) using circular dichroism spectroscopy at -110°C to +30°C. Using absorption spectra of the intermediates formed at the respective temperatures, circular dichroism spectra (300–800 nm) of pure intermediates were calculated.
The sign of the circular dichroic absorption bands changed upon formation of lumi-R, the primary photoproduct of P_r. This would be compatible with a Z→E isomerization taking place at this reaction step. The subsequent intermediates (meta-R_a and meta-R_c) as well as P_fr showed only small circular dichroism. Their absorption spectra were drastically shifted, but had similar spectral shapes. The results are discussed in terms of conformational changes of the phytochrome chromophore presumably taking place at the early steps of phototransformation P_r to P_fr.     

Phytochrome properties and the molecular environment

In vitro data support a scheme of phytochrome phototransformation involving intermediates in a sequential pathway. The fraction of total phytochrome maintained as intermediate under conditions of pigment cycling as well as the rate of the dark reversion of the far red-absorbing (Pfr) to the red-absorbing form of phytochrome (Pr) has been shown to depend on the molecular environment of the phytochrome molecules. Inverse dark reversion of Pr to Pfr has been observed in vitro. These results contribute toward an understanding of the observed paradoxes between physiological experiments and measurements of the amount and state of phytochrome in vivo. The in vivo spectrophotometric assay measures an average of the properties of phytochrome in different cellular environments, whereas a particular physiological response may be controlled by phytochrome molecules in one particular environment. It is therefore possible that all phytochrome is potentially active and triggers specific responses by virtue of its localization.     

Low temperature spectrophotometry of the phototransformation of Pfr to Pr in pelletable pea phytochrome

Manabe, K. 1987. Low temperature spectrophotometry of the phototransformation of P_fr to P_r, in pelletable pea phytochrome.
Low temperature spectrophotometry was used to study the phototransformation of P_fr to P_r in 1000–7000 g pelletable fractions extracted from dark grown pea ( Pisum sativum L. cv. Alaska) epicotyls which had been irradiated with red and then far-red light. At -170°C, far-red irradiation of the pelletable phytochrome which had been pre-irradiated with saturating fluence of red light before freezing caused formation of an intermediate (named I₆₆₀), the difference spectrum of which showed a marked ab-sorbance decrease at 740 nm and a concomitant small increase at about 660 nm. The inermediate I₆₆₀ was converted to another intermediate (I₆₆₀) when it was warmed above -80°C. The difference spectrum of this intermediate showed a positive peak at 670 nm. This intermediate was photoconverted to P_fr by red irradiation and also underwent dark reversion to P_fr at -60°C. I₆₆₀ formed P_r if the temperature was above -10°C. The basic features of the phytochrome intermediates resemble those obtained in vivo and in degraded purified phytochrome.     

Phytochrome: First-order phototransformation kinetics in vivo

Summary The deviation from first order commonly observed in phototransformation kinetics of phytochrome in vivo is due to a light-intensity gradient within the sample. This gradient was measured and was found to approach that predicted by the Kubelka-Munk theory of light scatter in turbid materials. The influence of this gradient is eliminated and first-order phototransformation kinetics are obtained, when either (i) thin samples of translucent (low optical density) material of high phytochrome content are measured directly; or (ii) thin samples of opaque (high optical density) or translucent material are sandwiched between two layers of light-scattering material. This result is consistent with the existence of only one population of photoreversible phytochrome molecules in vivo.     

The genetics of phytochrome signalling in Arabidopsis

The application of Arabidopsis genetics to research into the responses of plants to light has enabled rapid recent advances in this field. The plant photoreceptor phytochrome mediates well-defined responses that can be exploited to provide elegant and specific genetic screens. By this means, not only have mutants affecting the phytochromes themselves been isolated, but also mutants affecting the transduction of phytochrome signals. The genes involved in these processes have now begun to be characterized by using this genetic approach to isolate signal transduction components. Most of the components characterized so far are capable of being translocated to the cell nucleus, and they may help to define a new system of regulation of gene expression. This review summarises the ongoing contribution made by genetics to our understanding of light perception and signal transduction by the phytochrome system.