Plant Molecular Biology 42: vii–ix, 2000.
© 2000 Kluwer Academic Publishers. Printed in the Netherlands.
In one sense or another, everything in life is about evolution. Certainly, it is widely accepted that evolution is a
primary force that shapes the natural world, starting at the level of individual molecules and building from there
to genotypes and the phenotypes they underlie, to populations, species, and still higher taxonomic categories. At
the lower end of that spectrum, dynamic in their own right but molded in turn by evolutionary patterns of species,
are the complex interrelationships of multigene families. Evolution has always played a part in molecular biology,
albeit often in a fairly understated way as in the concept of ‘conserved’motifs – TATA boxes and the like. But that
rolehasbecomeincreasinglyimportant,as more and more genes from more and more taxa have been described. We
are now in the era of comparative genomics, and ‘evolutionary’ might justiﬁably be substituted for ‘comparative’.
And evolutionary biology is increasingly able to meet the needs of molecular biologists. While development,
physiology, and other ﬁelds have been transformed by the molecular revolution, evolution and systematics (the
study of the kinds and diversity of living things) have experienced their own explosive molecular biology-fueled
growth. Molecular technology has given evolutionists the ability, at long last, to look directly at the genotype
and cut out the phenotypic middleman; the impact on evolutionary theory has been dramatic. In systematics,
the powerful union of such molecular tools as polymerase chain reaction with computer technology has made it
possible to look beyond the tips of the ‘tree of life’ and construct phylogenetic hypotheses for large groups of
In this issue, we have attempted to give a few examples from among the many interfaces between plant molec-
ular biology and evolutionary biology. The ﬁeld is vast, and we have by no means covered – or even attempted to
cover – all of the bases. Some particularly prominent areas are missing entirely, such as the extremely rich area of
organellargenomeevolution, for whichseveral excellent reviews fortunatelyexist. The book is organizedinto three
major sections, beginning with some general topics. The editors ﬁrst present a ‘primer’ on molecular evolution and
systematics, which we hope will beusefulto those who may not be ﬂuent with the conceptsandterminologyof such
issues as Neutral Theory, paralogy/orthology, or phylogeny reconstruction. The second paper, by Spencer Muse,
contains both a statistical and an empirical component. The statistical component explains some of tools applied
to molecular evolutionary inference, while the empirical component summarizes what is known, and unknown,
about the pattern and process of nucleotide substitution in plants. The paper discusses such features as variation in
rates of evolution among genes and variation in rates of evolution among different plant species. In the ﬁnal paper
of the ﬁrst section, Doug and Pam Soltis describe the progress being made in molecular phylogenetics of plants.
They provide an overview of progress in handling large data sets involving several genes from each of hundreds of
species, offering hope that the complexity of such data sets presents not only the obvious advantages of improved
sampling and more characters, but even makes possible faster and more thorough analysis. They then update our
understanding of the relationships of key plant groups, such as land plants, ﬂowering plants (angiosperms), and,
within the angiosperms, families that include important economic or model plants such as maize and Arabidopsis.
The second section presents several case histories describing the evolution of protein-coding gene families – an
important topic, because gene families dominate the genomic landscape of plants. In the ﬁrst paper of this section,
Mary Durbin, Bonnie McCaig and Michael Clegg describe their work on the chalcone synthase family in the
common morning-glory. A great deal is known about the function of chalcone synthase – it regulates expression
of the biochemical pathway that governs ﬂower coloration – but there is still much to learn about the evolution
of the gene family. Durbin et al. reveal that the gene family contains highly divergent members, many of which
are differentially expressed. The gene family even has ‘black sheep’, in that some members of the family have