Seed coats: Structure, development, composition, and biotechnology

Although seeds have been the subject of extensive studies for many years, their seed coats are just beginning to be examined from the perspective of molecular genetics and control of development. The seed coat plays a vital role in the life cycle of plants by controlling the development of the embryo and determining seed dormancy and germination. Within the seed coat are a number of unique tissues that undergo differentiation to serve specific functions in the seed. A large number of genes are known to be specifically expressed within the seed coat tissues; however, very few of them are understood functionally. The seed coat synthesizes a wide range of novel compounds that may serve the plant in diverse ways, including defense and control of development. Many of the compounds are sources of industrial products and are components of food and feeds. The use of seed coat biotechnology to enhance seed quality and yield, or to generate novel components has not been exploited, largely because of lack of knowledge of the genetic systems that govern seed coat development and composition. In this review, we will examine the recent advances in seed coat biology from the perspective of structure, composition and molecular genetics. We will consider the diverse avenues that are possible for seed coat biotechnology in the future. This review will focus principally on the seed coats of the Brassicaceae and Fabaceae as they allow us to merge the areas of molecular biology, physiology and structure to gain a perspective on the possibilities for seed coat modifications in the future.