The regulation of cell cycle transitions is one of the most widely studied phenomena in biology, and studies in several model systems have revealed the basic machinery that drives these transitions. Although the core cell cycle machinery is conserved across evolution, its regulation has to be tightly coordinated in both space and time during multicellular development. To gain insights into the complex interplay that occurs between developmental signals and the basic cell cycle machinery requires a unique synthesis of two distinct fields of research that have largely evolved independently. A vast amount of information has been accumulated in the study of plant developmental patterning, as well as concerning the nuts and bolts of cell cycle transitions. Cell Cycle Control of Plant Development, edited by Dirk Inzé, attempts to bring together these two distinct fields in a series of review articles that provide comparative overviews of the components and regulation of the cell cycle machinery in diverse plant and animal systems.FIG1 

Cell Cycle Control and Plant Development (Annual Plant Reviews Vol. 32)
 Edited by Dirk Inzé
 Blackwell Publishing (2007) 384 pages
 ISBN 978-1-4051-5043-9
 £99.50/€134.40 (hardback)

Cell Cycle Control and Plant Development (Annual Plant Reviews Vol. 32)
 Edited by Dirk Inzé
 Blackwell Publishing (2007) 384 pages
 ISBN 978-1-4051-5043-9
 £99.50/€134.40 (hardback)

Although not a useful reference for emerging concepts, this book is an excellent source of information on the cell cycle machinery and its regulation

The book consists of 15 chapters written by researchers who study the cell cycle machinery and its regulation, and is broadly divided into two parts. The first seven chapters are dedicated to describing the various components that mediate cell cycle transitions, including the structural diversity among components and their regulation, and the complexes that these different proteins form. To a limited extent, the signals that regulate the expression and that modulate the biochemical activities of cell cycle components are also described. The second part of the book is mainly dedicated to studies that aim to link cell cycle regulation with specific developmental events and with plant hormones.

The spatiotemporal regulation of cell cycle transitions through G1 to S phase and through G2 to M phase is mediated by the regulated synthesis and destruction of phase-specific Cyclin proteins. Cyclins, in turn, form heterodimeric protein complexes with Cyclin-dependent kinases (CDKs) to produce pulses of CDK activity. Activated CDKs then phosphorylate proteins important for cell cycle progression. In chapter 1 (by Dénes Dudits and colleagues), the structural diversity of CDKs that have been identified in various plants is described, as grouped into eight classes. Subsequent chapters discuss the regulation of CDK activity, such as CDK association with Cyclins (chapter 2 by Jeroen Nieuwland, Margit Menges and James Murray), the binding of a CDK inhibitor to the CDK complex (chapter 3 by Hong Wang and colleagues), the regulated proteolysis of Cyclins and of CDK inhibitor (CKI)proteins (chapter 4 by Pascal Genschik and Marie Claire Criqui), and the reversible phosphorylation of CDKs (chapter 5 by Akie Shimotohno and Masaaki Umeda). Chapters 6 (by Elena Ramirez-Parra and colleagues) and 7 then cover the transcriptional regulation of cell cycle transitions. Chapter 7 by Wilhelm Gruissem, in particular, elaborates on the functions of the retinoblastoma-related protein (RBR) in the developmental regulation of germ cells and stem-cell maintenance. The discussion of the implications of the evolutionarily conserved function of RBR in both the maintenance of a differentiated cell state and cell cycle progression is illuminating.

Overall, the first seven chapters are well organized and complement each other nicely. The illustrations provided in chapters 3, 4 and 5 allow the reader to synthesize the complex and exhaustive information that is provided. However, the very nature of the subject matter discussed, which is mainly cataloging information, and the lack of a consistent format between the chapters, renders them difficult to read. Moreover, the regulation of the cell cycle machinery is discussed in individual chapters, which is the theme for the next part of the book. This leads to some redundancy, and therefore the book struggles to achieve the right balance between integrating the information on the cell cycle machinery and its regulation.

The second part of the book begins with the role of the plant hormone auxin in cell cycle regulation, with a specific focus on the process of lateral root initiation, which involves the reactivation of the cell cycle in a set of differentiated pericycle cells, as outlined in chapter 8 by Steffen Vanneste,Dirk Inzé and Tom Beeckman. This chapter also highlights the antagonistic roles played by the plant hormones auxin and cytokinin in this process and discusses auxin signaling, post-transcriptional mechanisms and polar auxin transport. Chapter 9 by Andrew Fleming turns to cell cycle regulation in leaf development, which is used as a model system to study the dynamic interplay between developmental signaling and different modes of cell cycle regulation. The author makes a sincere effort to provide in this chapter a conceptual framework for studying the cell cycle control of development, and discusses the existing experimental evidence on the causal relationships between the cell cycle and development within the framework of two alternative theories of the cellular basis of development (the organismal view and the cellular theory of development).

The next four chapters discuss the molecular mechanisms, significance and regulation of endoreplication (a condition in which no cytokinesis occurs between two successive rounds of DNA replication) in various developmental contexts, and the functions of auxin and cytokinins in establishing and maintaining the dividing populations of cells within the apical meristems. This chapter by Peter John also provides an in-depth account of the influence of these hormones on cell cycle regulators, both at G1 to S and G2 to M transitions, and concludes with a stimulating discussion on the mechanisms by which concentrations and ratios of auxin and cytokinin might function to influence growth and patterning in the shoot and the root apical meristems.

Over the years, much information has been accumulated from diverse plant species, animal models and unicellular model systems, both on the components and the regulation of the cell cycle. From this view point, the timing of this book's publication is appropriate as it brings together the complex diversity of the cell cycle under one roof. The synthesis of cell cycle regulation with environmental cues and with developmental patterning is attempted, both in individual chapters dedicated to describing the cell cycle machinery and also in the second part of the book that is dedicated to cell cycle control. This makes the book rather repetitive at times, which could have been avoided by a reduction in the number of chapters to achieve a better synthesis. And although it might not be a useful reference for students and teachers interested in learning about the emerging concepts in either field (cell cycle or development), this book can serve as an excellent source of information on the cell cycle machinery and its regulation. I would, therefore, highly recommend this book to researchers interested in exploring the developmental and environmental control of the cell cycle for use as a quick reference guide.