Advancements in expansin genes of plants.

Expansin gene is a kind of conserved multigene family with four sub-families α, β, γ and δ. As an important component in plant cell wall, expansin refers to a nonenzymatic protein with unique "loosening" effects on plant cell walls to accelerate the cell extension, increase its flexibility, and release the pressure by environment factors. The advancements of expansins support that expansins are involved in most of the physiological process in plants, such as seed germination, root hair promotion and extension, leaf formation, petiole off, pollen tube growth, fruit ripening，and other developmental process where cell wall loosening occurs. It is also involved in the process of drought, heat or disease resistance in plants. Mostly, expansin genes express inducible by the environmental factors, such as hormone, temperature, drought, pathogen and injuring.