Genetic analysis of trichome initiation

May 2000, Vol. 5, No. 5 1360 1385/00/$ – see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S1360-1385(00)01597-1 In plants, the control of cell fate is a central issue during embryo development, meristem function and the transition from vegetative to reproductive phases. The regulation of cell fate requires a balance of cell proliferation, differentiation, intercellular communication and morphogenesis control. All of these developmental processes are involved in the formation of unicellular trichomes in the shoot epidermis of Arabidopsis. The integration of these processes is complex, and progress in understanding control mechanisms has been slow. Trichome development has provided a simple model to gain mechanistic insight into the control of cell fate and morphogenesis. Because of their amenability to genetic analysis and the physical accessibility of the leaf epidermis, diverse molecular, pharmacological and cytological approaches have been used to study different aspects of trichome development. Here we summarize recent data on the molecular genetics of leaf trichome initiation and morphogenesis. Trichomes, defined as hair-like structures that extend from the epidermis of aerial tissues, are present on the surface of most terrestrial plants. Plant trichomes comprise a diverse set of structures, and many plants contain several types of trichomes on a single leaf. It has been difficult to demonstrate their function clearly, but several ideas have gained widespread acceptance. The presence of trichomes can increase the boundary layer thickness between the epidermal tissue and the environment, and can reduce heat and water loss. In many species, trichomes are thought to protect the plant against insect or pathogen attack, either by secreting chemical components or by physically limiting insect access to or mobility on vegetative tissues. The stellate trichomes of Arabidopsis do not have a secretory anatomy, but at a functional level, they might limit herbivore access to the leaf in the field.