Regulation of flowering time by light quality

The transition to flowering in plants is regulated by environmental factors such as temperature and light. Plants grown under dense canopies or at high density perceive a decrease in the ratio of red to far-red incoming light. This change in light quality serves as a warning of competition, triggering a series of responses known collectively as the 'shade-avoidance syndrome'. During shade avoidance, stems elongate at the expense of leaf expansion, and flowering is accelerated. Of the five phytochromes-a family of red/far-red light photoreceptors-in Arabidopsis, phytochrome B (phyB) has the most significant role in shade-avoidance responses, but the mechanisms by which phyB regulates flowering in response to altered ratios of red to far-red light are largely unknown. Here we identify PFT1 (PHYTOCHROME AND FLOWERING TIME 1), a nuclear protein that acts in a phyB pathway and induces flowering in response to suboptimal light conditions. PFT1 functions downstream of phyB to regulate the expression of FLOWERING LOCUS T (FT), providing evidence for the existence of a light-quality pathway that regulates flowering time in plants.     

A light-sensing knot revealed by the structure of the chromophore-binding domain of phytochrome

Phytochromes are red/far-red light photoreceptors that direct photosensory responses across the bacterial, fungal and plant kingdoms. These include photosynthetic potential and pigmentation in bacteria as well as chloroplast development and photomorphogenesis in plants. Phytochromes consist of an amino-terminal region that covalently binds a single bilin chromophore, followed by a carboxy-terminal dimerization domain that often transmits the light signal through a histidine kinase relay. Here we describe the three-dimensional structure of the chromophore-binding domain of Deinococcus radiodurans phytochrome assembled with its chromophore biliverdin in the Pr ground state. Our model, refined to 2.5 A resolution, reaffirms Cys 24 as the chromophore attachment site, locates key amino acids that form a solvent-shielded bilin-binding pocket, and reveals an unusually formed deep trefoil knot that stabilizes this region. The structure provides the first three-dimensional glimpse into the photochromic behaviour of these photoreceptors and helps to explain the evolution of higher plant phytochromes from prokaryotic precursors.     

Sequence analysis of the Microcystis aeruginosa FACHB-912 phytochrome gene supports positive selection in cyanobacteria

The phytochrome gene from Microcystis aeruginosa FACHB-912,isolated from algal blooms in Taihu Lake in China,was sequenced and found to code for a wavelength transition light receptor protein.The gene was composed of five distinct domains:a PAS fold domain,a GAF domain,a phytochrome domain,a His Kinase A(phosphoacceptor) domain,and a histidine kinase domain.Red-absorbing phytochrome,far-red-absorbing phytochrome,and photoconversion kinetics were monitored via the spectral characteristics of the protein.To detect positive selection,homologous sequences from cyanobacterium phytochrome genes were obtained from GenBank.Potential selective pressure was identified by phylogenetic analysis with maximum likelihood analyses.The frequency of the phytochrome gene being subjected to selective constraints suggests that positive selection is a potentially important mechanism that promotes the evolution of the cyanobacteria phytochrome gene.The sites identified in this study provide targets for further research on the structural-functional role of these residues,and on the correlation with the mechanism of algal blooms.     

Subcellular localization and functional analyses of structural domains of COP1 in transgenic tobacco

Plants have evolved an extremely exquisite light signal regulatory network to adapt to the changing ambient light conditions, in which COP1 plays a critical role of the light signal transduction. Based on the cloned pea COP1 cDNA sequence and its protein structure, four individual gene fragments encoding different structural domains of the COP1 were designed to fuse to the GFP gene. The plant expression vectors containing these fusion genes as well as the COP1GFP fusion gene were constructed and used to transform tobacco by Agribacterium as confirmed by Southern analyses. Antibodies were raised against the recombinant GFP-COP1 overproduced in Escherichia coli. Immunoblotting results demonstrated that all of the fusion genes were constitutively expressed in transgenic tobacco plants. We systematically investigated the different subcellular localization of these fusion proteins and the resulting phenotypic characteristics of these transgenic plants under light and dark conditions. Our data show that (1) the molecular mass of the tobacco endogenous COP1 protein is 76 kD. It is constitutively expressed in all of the tested tissues and the total cellular content of COP1 protein is not noticeably affected by light conditions. (2) The nuclear localization signal of COP1 plays a critical role in regulation of its nuclear-cytoplasmic partitioning. The subcellular localization of the COP1 protein containing nuclear localization signal is regulated by light in the epidermal cells of leaves, but, it is located in nucleus constitutively in root cells. (3) The coiled-coil domain is very critical to the function of COP1 protein, while the zinc binding RING finger domain only plays a supportive role. (4) The WD-40 repeats domain is essential to the COP1 function, but this domain alone does not affect photomorphogenesis. (5) Overexpression of COP1 protein not only inhibits the photomorphogenesis of the stems and leaves of the transgenic tobacco, but also results in the generation of short and clustered roots. In contrast, overexpression of COP1 protein without WD-40 repeats domain promotes the photomorphogenesis process in the stems and leaves and lead to root elongation and lack of lateral roots. The COP1-COP1 interaction happens not only in the nucleus, but also in cytoplasm.     

统计分析方法在植物电波信号研究中的应用

植物电波信号是一种相当复杂的信号，应用传统的电生理方法，已不能获取更多有用信息.应用统计分析方法对植物电波信号进行了时域和频域上的分析.分析发现植物电波信号属于低频信号，其功率谱主要分布在小于5 Hz频段，是一种随机性比较强的微弱信号，幅值处于μV级，并随时间变化剧烈，不同时刻的取值关系松散.     

水稻光敏色素A的克隆及其在光形态建成中的作用

克隆了OsPHYA基因，分析光暗诱导下该基因的表达、极低辐照度反应（VLFR）条件下萌发率测定、VLFR和高辐照度反应（HIR）条件下胚芽鞘伸长以及白化苗转绿过程中叶绿素含量测定等实验. 结果表明，OsPHYA基因在黑暗条件下根、茎和叶中的积累水平高于光照处理；OsPHYA在VLFR下能促进水稻种子萌发；而在VLFR和HIR反应中，OsPHYA抑制水稻胚芽鞘的伸长.对OsphyA突变体和野生型的主要农艺性状进行了比较分析，发现2种基因型仅在每株穗数方面有一定差异，说明光敏色素A对水稻农艺性状的影响不明显.     

Functional interaction of phytochrome B and cryptochrome 2

Light is a crucial environmental signal that controls many photomorphogenic and circadian responses in plants. Perception and transduction of light is achieved by at least two principal groups of photoreceptors, phytochromes and cryptochromes. Phytochromes are red/far-red light-absorbing receptors encoded by a gene family of five members (phyA to phyE) in Arabidopsis. Cryptochrome 1 (cry1), cryptochrome 2 (cry2) and phototropin are the blue/ultraviolet-A light receptors that have been characterized in Arabidopsis. Previous studies showed that modulation of many physiological responses in plants is achieved by genetic interactions between different photoreceptors; however, little is known about the nature of these interactions and their roles in the signal transduction pathway. Here we show the genetic interaction that occurs between the Arabidopsis photoreceptors phyB and cry2 in the control of flowering time, hypocotyl elongation and circadian period by the clock. PhyB interacts directly with cry2 as observed in co-immunoprecipitation experiments with transgenic Arabidopsis plants overexpressing cry2. Using fluorescent resonance energy transfer microscopy, we show that phyB and cry2 interact in nuclear speckles that are formed in a light-dependent fashion.     

光学技术对促进广西现代农业发展的思考

介绍植物光生态和光敏色素的研究现状,以及光生态膜、人造光源和植物超弱发光等光学技术及产品在现代农业生产方面的应用情况,提出广西发展光学技术及产品在现代农业中的应用,应加大科技投入力度,多层次开展研究开发工作,加强培养人才,做好科普宣传工作,抓好光学新技术及产品的普及应用和示范推广应用等工作。     

棉花GhGAI1基因克隆及其功能的初步分析

DELLA蛋白是赤霉素信号通路中重要的蛋白质作用因子,负调节植物体中赤霉素的水平,同时受到生长素、脱落酸和乙烯的共同调节。根据已知的生物信息数据,本研究克隆了棉花GhGAl1基因,序列分析表明它编码DELLA蛋白。构建GFP与GhGAl1融合蛋白重组质粒,利用根癌农杆菌介导的花浸泡转基因方法转化拟南芥columbia生态型植株,进行过量表达实验。结果表明,GFP—GhGAl1融合蛋白定位于细胞核并且在施加赤霉素后迅速降解,表明该基因编码蛋白参与赤霉素信号通路。     

Responses of ferns to red light are mediated by an unconventional photoreceptor

Efficient photosynthesis is essential for plant survival. To optimize photosynthesis, plants have developed several photoresponses. Stems bend towards a light source (phototropism), chloroplasts move to a place of appropriate light intensity (chloroplast photorelocation) and stomata open to absorb carbon dioxide. These responses are mediated by the blue-light receptors phototropin 1 (phot1) and phototropin 2 (phot2) in Arabidopsis (refs 1-5). In some ferns, phototropism and chloroplast photorelocation are controlled by red light as well as blue light. However, until now, the photoreceptor mediating these red-light responses has not been identified. The fern Adiantum capillus-veneris has an unconventional photoreceptor, phytochrome 3 (phy3), which is a chimaera of the red/far-red light receptor phytochrome and phototropin. We identify here a function of phy3 for red-light-induced phototropism and for red-light-induced chloroplast photorelocation, by using mutational analysis and complementation. Because phy3 greatly enhances the sensitivity to white light in orienting leaves and chloroplasts, and PHY3 homologues exist among various fern species, this chimaeric photoreceptor may have had a central role in the divergence and proliferation of fern species under low-light canopy conditions.     

Phytochrome signalling is mediated through nucleoside diphosphate kinase 2.

Because plants are sessile, they have developed intricate strategies to adapt to changing environmental variables, including light. Their growth and development, from germination to flowering, is critically influenced by light, particularly at red (660 nm) and far-red (730 nm) wavelengths. Higher plants perceive red and far-red light by means of specific light sensors called phytochromes(A-E). However, very little is known about how light signals are transduced to elicit responses in plants. Here we report that nucleoside diphosphate kinase 2 (NDPK2) is an upstream component in the phytochrome signalling pathway in the plant Arabidopsis thaliana. In animal and human cells, NDPK acts as a tumour suppressor. We show that recombinant NDPK2 in Arabidopsis preferentially binds to the red-light-activated form of phytochrome in vitro and that this interaction increases the activity of recombinant NDPK2. Furthermore, a mutant lacking NDPK2 showed a partial defect in responses to both red and farred light, including cotyledon opening and greening. These results indicate that NDPK2 is a positive signalling component of the phytochrome-mediated light-signal-transduction pathway in Arabidopsis.     

紫花苜蓿转录因子MsDREB1基因表达产物的亚细胞定位

利用生物信息学方法对紫花苜蓿MsDREBl进行了生物信息学分析．结果表明,该序列舍有AP2典型结构域,在N端存在核定位信号．为进一步验证该基因功能,构建MsDREBl与绿色荧光蛋白（GreenFluorescentProtein,GFP）基因融合的植物表达载体pCAMBIAl302-MsDREBl,再利用基因枪将其转入洋葱表皮细胞,在共聚焦扫描显微镜下观察MsDREBl基因表达产物在洋葱表皮细胞中的亚细胞定位．结果表明,MsDREBl基因表达产物定位于细胞核中,符合DREB家族转录因子特性．     

光在植物生长发育中的作用

光线既能作为植物细胞的能量来源,又能通过影响光敏素、隐花色素和紫外光受体等蛋白质构像,引起光信号传导,从而改变细胞激素水平和基因表达模式,在调节植物生长发育中具有重要作用.