The progress in photosynthesis research has been quite dramatic during the last two decades. The Nobel prizes awarded to Peter Mitchel (1978), to Johannes Deisenhofer, Hartmut Michel and Robert Huber (1988), to Rudolf Marcus (1992) and to Paul Boyer and John Walker (1997) have recognized— directly or indirectly—the structural or mechanistic discoveries related to the photosynthetic energy conversion. Actually, photosynthesis may be the first biological process described, not only in molecular terms, but even in atomic terms.
Much of the excitement around photosynthesis is based upon the connection between light and life. Light is an elusive 'substrate' that cannot be handled in the same way as conventional chemical substrates in biological metabolic reactions. Thus, during the last several years a new branch of photosynthesis research has evolved that not only deals with the actual process of energy conversion but also how the photosynthetic process is regulated. This new volume (Volume 11) in the series Advances in Photosynthesis and Respiration is devoted to this topic—the regulation of photosynthesis. Many chapters in the book describe this regulation from the view of gene expression and signal transduction. These are essential and topical issues of life sciences in general but the function of two cooperating genomes, the nuclear and plastidic ones, as well as light as a factor in signaling, make these central issues even more complicated when it comes to regulation of photosynthesis. The book covers a wide range of topics about regulation of photosynthesis, occurring under natural daily conditions or when plants are exposed to stress conditions. The 32 chapters, contributed by authors who are leading experts in each particular field, have been divided into six distinct parts in this book.
Part I—Evolution, complexity and regulation of photosynthetic structures—gives a comprehensive overview to the different topics in the book and emphasizes the complex evolution and genetics the of photosynthetic machinery.
Part II—Gene expression and signal transduction—is devoted to specific light receptors, signal transduction and expression of photosynthetic genes which occur both in the nuclear/cytosol compartment and in the chloroplast. Several chapters are devoted to the transcription machinery and the two plastid RNA-polymerase complexes, to the regulation of photosynthesis genes by redox signaling both in chloroplasts and in the prokaryotic systems, as well as to the sugar sensing mechanisms. Chapters also cover important regulatory aspects imposed by post-transcriptional modifications and degradation of mRNA molecules, and the translational regulation mechanisms operating in chloroplasts.
Part III—Biogenesis, turnover and senescence— is closely connected to the question of regulation. The chapters included emphasize how the complicated membrane structures, composed of both nuclear and chloroplast encoded proteins, are synthesized and put together with a correct orientation in a membrane and how they bind an array of different redox ligands and pigments. Several of the chapters are devoted to genetic and biochemical aspects on lipid and pigment biosynthesis, on membrane transporters and on a group of relatively 'new' photosynthetic enzymes that assist in the assembly and turnover of membrane protein complexes. The latter group is represented by an extremely complicated set up of auxiliary enzymes present in very low abundance in connection with the photosynthetic machinery such as desaturases, kinases, phosphatases, isomerases, chaperones and proteases. This section also covers regulation of the latest phases of development in chloroplasts, also called senescence.
Part IV—Regulation of Carbon metabolism— Although the previous Volume 9 (Photosynthesis: Physiology and Metabolism, eds. RC Leegood, TD Sharkey and S von Caemmerer) in Advances in Photosynthesis already gave a comprehensive view of carbon metabolism and its regulation in plants, some strategically important aspects are also included in this volume. These include chapters that particularly emphasize the use of mutants in studies of photosynthetic regulation and the role of carbonic anhydrases in C02 fixation. Two chapters are devoted to the structure and regulatory mechanisms mediated by thioredoxins, universal regulators of photo-synthetic enzymes in carbon fixation and which more recently have been discovered to be involved in regulation of a vast number of other photosynthetic processes as well. Posttranslational modification of phosphoenolpyruvate carboxylase by reversible phosphorylation provides an example of a stringent regulatory mechanism of C4 metabolism, a mechanism highly used also in the regulation of other photosynthetic processes.
Part V—Acclimation and stress responses— Photosynthetic organisms experience a number of abiotic stress factors related to temperature, -deficiency and drought. Even light—an absolute necessity for photosynthesis—can be harmful to oxygenic photosynthetic organisms leading to photoinhibitory damages to the photosystems. Several chapters address questions of how stress induced damages can be minimized or repaired. These include the enzymatic mechanisms of reversible thylakoid protein phosphorylation, zeaxanthin-violaxanthin interconversion, redox sensing of reactive oxygen species and consequent acclimation processes, up-regulation of stress-related proteins and regulatory modifications in the electron transport pathways of the thylakoid membrane.
Part VI—Photosynthetic regulation and genomics—methodological implications for the future— takes into consideration the conceptual and methodological development that is influencing photosynthesis research by the dramatic revolution driven by genomics. Two chapters are devoted to the functional genomics of Arabidopsis and Synechocystis 6803, the model organisms with a complete genome sequence available and also frequently used in photosynthesis research. Certainly we are only in the beginning of an era where we will address questions in photosynthesis and its regulation by new and extremely efficient approaches. The book sets the scene for this new era of photosynthesis research.
This new volume in Advances in Photosynthesis and Respiration is the first that takes a broad perspective on regulatory aspects of photosynthesis and will provide a unique and updated frame of information in a rapidly growing area of photosynthesis research.
As editors of this volume 11 of Advances in Photosynthesis and Respiration, we want to express our sincere thanks to all the authors for their time and expertise in contributing their chapters on various regulatory aspects of photosynthesis. Special thanks are also due to Drs. Torill Hundal and Eira Kanervo for their excellent assistance, support and sense of humor in various phases and moments involved in the preparation of this volume. Govindjee is particularly acknowledged for his enthusiasm and encouragement, and Larry Orr for all possible technical help and patience with electronic communication which did not always work that perfectly.
Eva-Mari Aro University of Turku, Finland Email: evaaro @utu.fi
Bertil Andersson University of Linkoping, Sweden Email: [email protected]
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