The Plant Cuticle - not exclusive to aerial organs

The plant cuticle forms a multi-layered structure of lipid components at the outermost surface of plant organs in continuation with the cell wall. A high diversity in structure and composition of its main components, the aliphatic polyester cutin and waxes, has been recognized as well as its protective functions against biotic and abiotic stresses. During recent decades, many aspects of the cutin and wax biosynthetic pathways have been elucidated and some additional functions have been described. For example, the cuticle does not only play a role in stress protection, but also in organ development by preventing organ adhesions and fusions. Although the expression of cutin biosynthesis genes in root tips has been occasionally reported, the cuticle has been exclusively associated with epidermal tissues of the shoot, with protodermal cells of the embryo as their progenitor. We have recently shown that a cuticle is also present at the outer root cap cell layer and the basal part of the embryo. Like in the shoot cuticle, the main component of the root cap cuticle (RCC) is an aliphatic polyester that consists of typical cutin monomers, but also some atypical monomers. The RCC of young primary roots and emerging lateral roots plays important roles in root physiology and development. During the critical first days after germination, the RCC serves as a diffusion barrier, protecting the vulnerable seedling meristem and helping the seedling to adapt to environmental challenges. In lateral root formation, the RCC plays also an important role as a specialized surface structure that prevents adhesions of the newly forming organs to the main root. Despite considerable differences in the ultrastructure, composition and physical properties, cuticles of various organs have similar physiological roles in stress protection and development. These findings place the cuticle in a new context, as being a general surface structure of primary tissues that may be replaced by other - potentially more specialized - structures during plant development.