Expansins in Plant Growth and Development: an Update on an Emerging Topic

Expansins are a class of proteins identified by their ability to induce the extension of isolated plant cell walls. Expansins are encoded by an extensive multigene family in higher plants, several members of which have been shown to be expressed in a tissue‐specific manner. Besides playing an apparently key role in wall expansion, and hence in cell growth, expansins have been implicated in an increasing number of processes during plant growth and development. These include: leaf organogenesis, fruit softening, and wall disassembly. A second class of closely related proteins (referred to as β‐expansins) has been identified. Other recent advances in expansin research include the recovery of transgenic plants with altered level of expansins, and the production of recombinant expansins in het‐erologous expression systems.