The importance of emerging model systems in plant biology.

Model systems in plant biology include a range of species spanning from “well-established” to “emerging” models, depending on the degree to which they have been developed. There are two phases to building a model system: initiation and maintenance. Model species are initiated usually with a novel and often classic contribution to science (that is, they have provided insight into a process that was previously poorly understood). Mendel’s insights into genetics that came from analysis of the phenotype of pea seed coats is a good example. To be sustained, model systems must be experimentally tractable in general and also have a unique area in which their contributions are outstanding. They must be tractable in enough arenas—genetics, development, culture, transformation, and so on—so roadblocks do not prevent progress. For example, Xenopus oocytes are outstanding for localization of determinants, and the dearth of genetics can be circumvented with microinjection. Model species must be recognized by the scientific community (in print by peer review, by representation in symposia, and with funding) to emerge as a new model and then to grow into wellestablished systems. Emerging Model Systems in Plant Biology, a special issue of Journal of Plant Growth Regulation, helps to inaugurate a new format for Springer-Verlag centered on bringing together reviews on a timely topic. Why are emergent model systems for plant biology a timely topic? Indeed, why should we have more than one model plant system? We will know the complete sequence of Arabidopsis thaliana soon. This system has good genetics and excellent molecular tools (cDNA and genomic libraries, bacterial artificial chromosomes, microarrays, ESTs, and so on). Prominent scientists have voiced the opinion that progress in plant biology was slowed to a snail’s pace for years by working on too many species at one time. Clearly, having focused on A. thaliana has pushed plant biology forward by leaps and bounds in a short time. In the age of modern molecular genetics when we can clone a gene from one plant and use molecular and biochemical techniques (that is, polymerase chain reaction and antibodies) to study that same gene in another species, why bother with more than one plant model system? It is not an overstatement to say that plants— from green algae to angiosperms—represent the most diverse biochemistry, architecture, life history (including alternation of generations), reproductive biology (sexual and asexual), and body plans on Earth. Flowering plants have an estimated 300,000 species compared with only 4,500 for our closest relatives, the mammals, a group of approximately the same age. No one plant, not even Arabidopsis thaliana, can encompass this enormous diversity at the whole plant, physiologic, chemical, genetic, or molecular level. It behooves us to understand this biodiversity so that we can better use it and protect it as the population and environmental impact of our own species explodes into the next century. Mankind uses plants for fuel, building materials, clothes, medicine, decoration (including beauty products and holiday talismans), recreation, food, and drink. It is hard to imagine life without plants—indeed, plants make Online publication 9 March 2001 *Corresponding author; e-mail: mandoli@u.washington.edu J Plant Growth Regul (2000) 19:249–252 DOI: 10.1007/s003440000038