生物專(zhuān)業(yè)外文翻譯--葉綠體的形成（英文）

1、EMBO open EMBO Member‘s ReviewThe making of a chloroplastThis is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits distribution,andreproductioninanymedium,provi

2、dedtheoriginalauthorandsourcearecredited.Thislicensedoesnot permit commercial exploitation or the creation of derivative works without specific permission.Mark T Waters and Jane A Langdale*Department of Plant Sciences, U

3、niversity of Oxford, South Parks Road, Oxford, UKSince its endosymbiotic beginning, the chloroplast has become fully integrated into the biology of the host eukaryotic cell. The exchange of genetic information from the c

4、hloroplast to the nucleus has resulted in considerable co-ordination in the activities of these two organelles during all stages of plant development. Here, we give an overview of the mechanisms of light perception and t

5、he subsequent regulation of nuclear gene expression in the model plant Arabidopsis thaliana, and we cover the main events that take place when proplastids differentiate into chloroplasts. We also consider recent findings

6、 regarding signalling networks between the chloroplast and the nu- cleus during seedling development, and how these signals are modulated by light. In addition, we discuss the me- chanisms through which chloroplasts deve

7、lop in different cell types, namely cotyledons and the dimorphic chloro- plasts of the C4 plant maize. Finally, we discuss recent data that suggest the specific regulation of the light-dependent phases of photosynthesis,

8、 providing a means to optimize photosynthesis to varying light regimes. The EMBO Journal (2009) 28, 2861–2873. doi:10.1038/ emboj.2009.264; Published online 10 September 2009 Subject Categories: signal transduction; plan

9、t biology Keywords: chloroplast biogenesis; photomorphogenesis; photosynthesis; plastid-nucleus signaling; transcription factorIntroductionAs a defining feature of plants, the chloroplast represents a marvel of evolution

10、. Since its origin as a cyanobacterial symbiont about 1 to 1.5 billion years ago (Douzery et al, 2004; Yoon et al, 2004), this organelle has become fully integrated into the life cycle of photosynthetic eukaryotes and ha

11、s essentially underpinned global ecosystems. Photosynthesis comprises two conceptually distinct phasesthat occur entirely within the chloroplast. The light-depen- dent reactions take place on the thylakoid membrane, in w

12、hich light energy drives electron transport between a series of multi-subunit protein complexes. In two of these complexes, photosystem I (PSI) and photosystem II (PSII), protein-bound chlorophyll pigments are excited by

13、 light and initiate electron flow, so generating ATP and reducing equiva- lents. This chemical energy is then used in the light-indepen- dent reactions that take place in the chloroplast stroma, in which CO2 is fixed by

14、Rubisco to generate sugars. Subseq- uently, this carbohydrate is either immediately exported to the cytosol or is stored within the chloroplast as starch. Beyond photosynthesis, the chloroplast is also the site of fatty

15、acid biosynthesis, nitrate assimilation and amino-acid biosynthesis. Given the importance of plant products to human beings, photosynthetic development and the biogen- esis of chloroplasts have received intense scrutiny.

16、 In seed plants, chloroplasts develop from a non-photosynthetic form called the proplastid, which is transmitted between genera- tions through the ovule and is maintained in meristematic stem cells. How does a chloroplas

17、t develop from a proplastid? How is photosynthetic competence reached and sustained? These are certainly complex and open questions, but two central themes emerge. First, the co-ordination and integration of multiple par

18、allel processes, none of which operates in isolation, are absolutely necessary. This theme is most clearly shown by the fact that mutations in single chloroplast compo- nents can have major ramifications beyond the immed

19、iate process in question. Second, constant interorganellar crosstalk occurs both during the initial construction of the chloroplast and to maintain form and function in mature tissues. Coupled with the need to respond to

20、 a constantly variable environment, this crosstalk reflects the existence of two genomes and the need to regulate dynamically the relative input from each towards constituent parts of the chloroplast. This review covers

21、some of the major cellular and developmental aspects of chloroplast biogenesis that encompass the above themes.Light signalling during photomorphogenesisIn seed plants, light is a prerequisite for the synthesis of chloro

22、phyll, and chloroplasts do not develop in the dark. Photomorphogenesis describes the developmental prog- ramme undertaken by seedlings exposed to light, and is typified by the inhibition of hypocotyl growth, the develop-

23、 ment of chloroplasts and the opening of cotyledons (in eudicotyledonous species). Light is perceived by a suite Received: 12 July 2009; accepted: 12 August 2009; published online: 10 September 2009*Corresponding author.

24、 Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK. Tel.: þ 44 1865 275099; Fax: þ 44 1865 275074; E-mail: jane.langdale@plants.ox.ac.ukThe EMBO Journal (2009) 28, 2861–2

25、873 | in addition, COP1 preferentially interacts with the unphosphorylated form of HY5, further suppressing levels of biologically active HY5 (Hardtke et al, 2000). In parallel, PIF3 is bound to G-box sequences in targe

26、t promoters, inhibiting transcription of photomorphogenesis-related genes. (B) Blue light exposure triggers the photoactivation of CRY1, which leads to the exit of COP1 from the nucleus and thus allows HY5 levels to incr

27、ease. HY5 is dephosphorylated, increasing its biological activity and further reducing its affinity for COP1; more HY5 is then available to bind to G-box motifs and promote transcription of genes such as light-harvesting

28、 chlorophyll-binding1 (Lhcb1/CAB1), a major antenna protein of PSII. Note that HY5 can also negatively regulate transcription of target genes and is necessary, but insufficient to regulate transcription alone (Lee et al,

29、 2007). Meanwhile, Pr is converted into the biologically active Pfr form by red light, which translocates into the nucleus and binds PIFs (such as PIF3). Phy-bound PIF3 is phosphorylated, rendering it susceptible to ubiq

30、uitination and subsequent degradation. As a result, transcription of genes such as those involved in chlorophyll biosynthesis can proceed. Phy-dependent repression of COP/DET/FUS proteins (revealed by epistasis) is depic

31、ted by a dashed arrow. Note that PIF3- regulated genes are not necessarily HY5 regulated, even though both transcription factors bind DNA through the G-box. In addition, there is some evidence that phyB may interact with