Phytochemistry has moved on

Evolution of Metabolic Pathways (Recent Advances in Phytochemistry) (Vol. 34)Edited by John Romeo, Ragai Ibrahim, Luc Varin and Vincenzo De Luca, Pergamon Press, 2000. US$275.00 hbk (xii + 467 pages). ISBN 0 08 043860 1Advances in phytochemistry have often arisen from developments in areas that at first glance did not seem closely related, but have later contributed greatly to advancement in the field. To illustrate this point, it is interesting to examine the Recent Advances in Phytochemistry series. In the early volumes, biogenetic pathways based on similarity to organic chemical sequences were recognized. The biochemistry described was largely based on isolation and purification of enzymes. Considerable emphasis was placed on chemotaxonomic application of the data, in an optimistic and now somewhat naive way, to resolve systematic and evolutionary problems in various plant groups.In this 34th volume, Evolution of Metabolic Pathways, the results of a major surge forward in understanding based on developments in plant molecular biology are presented. The emphasis has changed from that previously described to isolation and sequencing of the actual genes responsible for enzymatic steps involved in the production of a broad variety of plant secondary compounds. Additionally, expression of genes, and requisite generation of proteins from these genes, is explored. Evaluation of substrate specificities for the resultant proteins is now of major interest. Gene sequences modified in the course of evolution are seen to arise by gene duplication followed by mutational changes within an organism, as well as by changes in the DNA of genetically isolated organisms.Early studies compared similarities of organic constituents and biogenetic pathways. Today, gene sequences from distinct evolutionary lines can be compared using cladistic analyses, to produce phylogenetic trees that permit estimation of the evolutionary pathways for the genes and proteins leading to specific enzymatic changes, as well as for the resulting secondary metabolites. Comparison of sequences from genetically isolated organisms and their hybrids provides a valuable method for establishing the phylogeny of plant taxa as well. Interestingly, we can now use this evolutionary information to study the origins and distributional patterns of the compounds, the inverse approach to that used in chemosystematic studies in 1966, when this series began.The tools and approaches needed to advance these studies have undergone major changes as well. There has been a metamorphosis from traditional organic chemistry and biochemistry, through a series of more advanced separation and characterization techniques, determination of the range of substrates and identification of products, and estimation of gene phylogenies by cladistic methods, to PCR, RT-PCR, DNA cloning, and expression of these DNA segments in appropriate organisms.This new volume brings together contributions from plant biochemistry, molecular biology and evolutionary studies, in a remarkable and seamless way to present a valuable overview of the present-day status of phytochemistry and, in a broad sense, plant secondary metabolism. In a series of 14 chapters, the discussion progresses from the roles of the compounds produced, through a review of most of the major classes of enzymes involved in plant secondary metabolism. These include chalcone synthase-related enzymes, macrolide and polyketide synthases, enzymes involved in formation of terpenoid precursors and terpene cyclases, plant phytochromes P450, the enzymes involved in synthesis of cyanogenic glycosides, certain dioxygenases, acyltransferases, glucosyltransferases, methyltransferases and sulfotransferases, as well as a discussion of brassinosteroids in plants. This selection represents the most prominent enzymes of the majority of plant biosynthetic pathways. The chapters are useful reference sources for techniques and experimental methods that are both up to date and applicable to studying the origin and evolution of plant secondary metabolites.The editing skills of John Romeo et al. contribute unity of writing style, chapter content and organization, and greatly enhance the quality of the volume. In spite of the inherently complex nature of the topic, the chapters are well written and edited and relatively easy to read. Because of the broad scope of the materials discussed and linked to the evolution of metabolic pathways in plants, this volume should be of interest to a similarly broad array of investigators. This includes those who consider themselves to be phytochemists, as well as plant biochemists, physiologists and molecular biologists. Those interested in the evolution and systematics of plants will find much information of value. To my knowledge, there is no single volume that is as comprehensive and extensive in coverage for this exciting area of research.